Accurizing
Encyclopedia
Accurizing is the process of improving the accuracy of a firearm
or airgun.
For firearms, accuracy is defined as the ability to hit exactly what one is aiming at. Further, accuracy and precision
, or the ability to hit the same place over and over again in a repeatable fashion, are the goals of accurizing.
Accurizing generally concentrates on four different areas:
The key to an accurate firearm is consistency. Getting everything to happen the same way for every shot is key to producing small groups, and there are a large number of issues to be addressed in achieving an accurate firearm. The keys to firing an accurate shot are a firm but not overtight grip, the ability to get a good sight picture, and a controlled squeeze of the trigger. The ability to manage recoil is also important in heavily recoiling calibers, both to aid in possible additional shots, and to prevent the user from developing a fear of the recoil.
group). Groups for rifles are traditionally shot at 100 yards, where a minute of arc equals just over one inch, and the one MOA group is a traditional benchmark
of accuracy. Handguns are generally used at closer ranges, and are tested for accuracy at their intended range of use. Also of importance is the number of shots fired. Statistical likelihood says the fewer shots that are fired, the smaller the dispersion will be. 3 or 5-shot groups are acceptable for zeroing the sights and rough accuracy estimates, but most shooters consider 10-shot groups to be the minimum for accuracy comparisons.
wadcutter
rounds in three different revolver
s, a Smith & Wesson
Model 686 and Model 52, and a Colt Python
Target model, with six, five and eight inch long barrels, respectively. Ten groups of five shots were fired and measured from each revolver with each ammunition. Click on the image at right to see a larger view of the graph of average group sizes for each type of ammunition and each revolver. The average group size for the overall test was 2.85 inches (72.4 mm).
Based on average
group size, the winner was the Model 686, which shot an average group of 2.69 inches across the brands of ammunition, with a standard deviation between ammunition types of 0.54 inches. However, the Model 52, while shooting slightly larger groups at 2.88 inches, was far more consistent across the brands, with a standard deviation
of only 0.30 inches, and was the most consistent performer of the test. But, if you were able to tune your ammunition to the gun, the clear winner was the Python, which averaged just 1.69 inches with its favored brand of ammunition. The Python was also by far the pickiest, however, turning in the largest groups at 6.08 inch and 4.0 inch averages with its least favorite brands, for a standard deviation of 1.6 inches.
Based on this test, answering the question "Which is the most accurate?" becomes a matter of opinion. The answer that would most likely be given would probably be the 686, as it shot the best average groups. However, as the Python showed the best performance with one brand of ammunition, it might be the best choice if that brand of ammunition were acceptable for the application in question. If a consistent supply of ammunition were a problem, then the 52 might be the best choice, since it showed the least sensitivity to differences in ammunition.
will need to be accurate on the first shot from a cold, clean barrel, while one used for target shooting may be allowed fouling shots before the first shot for record is fired. Issues of portability or restrictions of certain competitions may limit the alterations that can be made. In addition, every firearm is different, and processes that yield huge results on one may have no impact on another
Another issue in measuring accuracy is the position in which the shots are fired. The most accurate shooting position is a supported position, such as firing from a benchrest with the firearm well supported by a shooting rest or sandbags; this eliminates much of the shooter's potential for error and will generally result in much smaller groups than firing from an unsupported position. Even for a firearm that is going to be shot offhand, accuracy testing from a machine rest will provide an idea of the ultimate attainable accuracy.
and external ballistics
, and handloading
, and just like accurizing a firearm, the goal is to produce the most consistent possible results. The shooter must also be consistent, and this means that the fundamentals of marksmanship have to be followed rigorously; any failure on the part of the shooter to remain focused and consistent can result in a bad shot. It's common to use a benchrest or a vise when evaluating ammo or a weapon for accuracy in order to eliminate human error.
, which emphasizes speed and uses relatively close targets with large scoring zones on the targets, to bullseye
shooting, which uses distant targets with tiny scoring zones. While both types of trigger need a predictable pull, bullseye shooters demand a much higher degree of precision.
The takeup is the least critical stage of the trigger pull, and individual preferences vary widely. Two stage triggers, for example, consist of a noticeable takeup, followed by a distinct increase in the force required to pull the trigger, followed by the break. A single stage trigger, on the other hand, has no discernible movement before the break. Fully adjustable triggers will provide a two stage pull, and the option of reducing the first stage travel to zero, essentially making the trigger a single stage trigger.
The break is a far more critical stage of the pull, as it happens just prior to the shot being fired. Here again, individual preferences vary; some shooters prefer a soft break, where there is a smooth but discernible amount of trigger travel during firing, while others prefer a crisp break, with a heavier weight and little or no discernible movement.
The overtravel can be the most critical factor in the trigger pull, as any movement caused at this point will happen as the shot is fired. This is especially important with firearms where there is a sudden release of resistance when the sear breaks, such as in double action triggers. An overtravel stop will arrest the motion of the trigger just after the break, and prevent movement.
While adjustable triggers may provide the greatest level of control, much can be done with standard non-adjustable triggers. Careful hand fitting and polishing of parts, addition of high precision or adjustable aftermarket parts, or fabrication of new parts can greatly improve most triggers. Care should be taken, however, since trigger work requires a great deal of care and precision, and a bad trigger job can easily render a firearm highly unsafe or unusable.
The firearm's sights allow the user to align the firearm with the target, and in some cases all that separates a "target" firearm from a standard model is improved sights.
Adjustable sights are essential for most target shooting, as they allow the point of impact to be adjusted to fall in the middle of the target when variables such as target range and ammunition type vary. Firearms with sights that are non-adjustable, or only coarsely adjustable, will not be able to reliably center the point of impact on the target. In addition, good visibility and a crisp sight picture help the user use the sights more reliably.
Typical rifle hunting sights, consisting of a square blade or bead front sight and an open notch mounted in front of the action, are good for quick alignment, but are far from ideal for precision shooting. An aperture sight mounted on the receiver or tang of the rifle, closer to the shooter's eye, will provide a much longer sight radius, which improves the shooter's ability to precisely align the sights. These sights often provide far more precise and repeatable adjustments than stock open sights. Telescopic and reflex sights offer advantages to shooters with poorer eyesight, as they bring the target and reticle into the same plane of focus, as well as providing the option of magnification. The downside to these is the additional weight and bulk they add.
or grip is one that allows the shooter to have a relaxed but firm grip on the firearm. This can range from minor changes such as texturing grip surfaces or adding a wide, beavertail type grip safety to a 1911, all the way to a custom built, anatomically designed grip that "fits like a glove". Key features are:
, or by adding texture to the grips. Traditionally wood grips and stocks are provided with checkering, a process where "V" shaped grooves are cut into the wood at an angle to each other, leaving a pattern of pyramidal projections in the wood. Another process uses a punch to leave a random pattern of dents in the surface, called stippling; this process is better suited to complex curves than checkering, and is often found on anatomical grips. Handguns with plastic frames will often have stippling or checkering molded into the frame.
Competition handgun grips are anatomically shaped, and are often custom fitted to the shooter's hand. An ideal grip will fit the contours of the shooter's grip, so that the knuckles fall into position the same way every time. The ideal grip should allow the shooter to repeatedly grasp the gun, bring it up to shooting position with eyes closed, and be correctly aligned and on target when they eyes are opened; this means the grip provides a consistent placement, and minimal corrections when aiming. Contrary to commonly stated rules of thumb, the handgun should not line up with the forearm when gripped, but rather point slightly outwards, so that when held to shoot, the sights line up with the shooter's eye. In cross-dominant shooters, the angle will be more pronounced. Thumbrests, finger grooves (if well fitted), and palm rests all provide control over recoil. An adjustable palm rest is a desirable feature as well, as it allows the grip to be adjusted to fit the shooter's hand as it swells and contracts over time.
Rifle stocks have similar issues of fit, and though the use of sights makes this less vital than in a shotgun, a good fit still helps the shooter to relax and concentrate on fundamentals. The shape of a rifle stock should be suited to its intended use. High combs and vertical pistol grips are ideal for high mounted target sights or scopes and careful, deliberate shooting such as encountered in traditional target shooting, metallic silhouette
, or varmint hunting
, as they provide a maximum point blank range and ideal trigger control. However, these features are not well suited for a typical hunting or action shooting
rifle, where the rifle must be brought from a ready position to a shooting position quickly and smoothly. This use favors low sights or scopes, and a shallow pistol grip angle. Rounded forearms are well suited for firing from offhand, while a square-bottomed forearm provides a stable base for shooting off of a sandbag or other rest.
Recoil is also a key issue in rifle stock design. Heavy recoiling rifles should have wide butts, with a good recoil pad to absorb the force of recoil, and a comb that is straight or slopes down towards the action, so that it does not push into the shooter's face under recoil. Other features of target or varmint stocks, such as thumbhole grips, can actually injure the shooter if used in a heavy recoiling hunting rifle.
Some target shooting disciplines allow the use of various devices to help support the rifle, and these are often mounted to an accessory rail beneath the forend. Target slings, unlike carrying slings, are used just on the off hand, usually with a hand stop, and provide stability to the shooter's hold. Palm rests are another device that can be attached to the rail, to allow a shooter to lower their off hand and place their elbow into their body for support. Target stocks also are available with a large degree of adjustment, including length of pull, drop, comb height and angle, and buttplate angle and curvature.
and firing pin or striker
, and using a more powerful spring. Further reductions in lock time, to near zero levels, can be achieved with electrical primers.
must be kept to a minimum. This can be achieved by carefully hand selecting parts, and fitting them together. The best fits are generally attained by selecting slightly oversized parts (or altering stock parts to form an interference fit
) and then lapping
the mating surfaces to attain the desired fit. Tolerances cannot be too tight, however, or functionality will be compromised; this is very important in automatic
and semi-automatic firearm
s, where there is a certain amount of energy extracted from the firing of the cartridge that must be used to cycle the action. Overly tight tolerances mean that there is no place for lubricant and dirt to be, and this can bind the parts.
In some cases, stock parts are not sufficient for the task of producing a finished product with sufficiently tight tolerances. In this case, it may be necessary to use specially fabricated parts, built either with minimal tolerances, or parts that are oversized and intended for hand fitting.
The barrel is one of the most important factors for accuracy, as a poorly made barrel may be beyond correction. Even a quality barrel must be well matched to the cartridge it will be firing. In most cases, it is not practical to fix a barrel whose bore is worn out, poorly or unsuitably rifled, or the wrong bore diameter; the primary exception to that is rimfire barrels, which can be inexpensively bored out and re-lined with a commercial barrel liner. If the barrel is unsuitable and relining is not an option, then an aftermarket or custom barrel is the best solution. However, if the bore is good, then there are a number of operations that can be done to the barrel to improve upon its accuracy.
A slight gain in the rifling twist, or a slight tapering down of the bore, will still ensure the tight fit of bullet to bore, so when selecting a barrel, the tighter or faster twist end should be chosen for the muzzle.
The twist of the rifling must match the intended ammunition for best accuracy. Rifling with too slow a twist will not stabilize long bullets, causing them to precess in flight; at its worst, this can result in the bullets tumbling in-flight and keyholing, where bullets strike the target sideways. Too fast a twist can also be a problem, as it can magnify problems in the bullet. A bullet whose center of mass is slightly off-center will diverge at a rate proportional to the rifling twist, so excess twist will result in greater dispersion. In practical terms, this is only a problem for rifles chambered for common military calibers where a variety of different loads exist. For example, M-16A1 rifle is unable to accurately fire bullets that are heavier than 55gr due to barrel twist that is too slow to stabilize heavier bullets. Precision rifles typically come with barrels that are either tailor-made for a specific ammo load or made according to the buyer's specifications.
Barrels can also benefit from lapping
, not only because it makes the bore a more consistent diameter, but also because it polishes the bore. Barrel lapping should be done with the tool moving in the same direction as the bullet will move, so that any imperfections in the barrel will be smoothed so that they don't interfere with the passage of the bullet. A smooth, polished bore will not only hold the bullet better, but also reduce barrel fouling.
cleanly. Once the bullet is engaged in the rifling, with a good seal and coaxial fit, it must stay that way. It is often possible to shorten a barrel slightly by removing material from the breech end and re-cut the chamber, which can correct many problems in the original chamber.
While many barrel manufacturers recess the crown to protect it from accidental damage, it can still be damaged over time by cleaning rods that are too hard. It is also not uncommon for factory crowns to be cut slightly off-center, so that one side of the bullet exits slightly earlier than the other, and this will result in the bullet being pushed away from that side, causing a significant deflection in its path. A crown may be re-cut with relative ease, and this can fix any problems caused by a defective or damaged crown, by ensuring an even release of the bullet.
the barrels. The amount of good this does depends on the technique used to make the barrel; the hammer forging method of manufacture, a fast method commonly used by large manufacturers, leaves a significant amount of stress in the barrels, which could be addressed through stress-relieving heat treatment.
s, such as 416, have been shown to have a longer life than the traditional 4140 chrome
/molybdenum
steels used for barrels. While the stainless barrels are not any more accurate than a 4140 barrel, they will maintain their accuracy longer in many applications, as they are more resistant to erosion caused by the heat of firing high powered cartridges. One notable exception to this is the .50 BMG
cartridge; competition shooters often fire high precision lathe
turned bullets made from harder brass, bronze, or steel in this caliber, and the 4140 steel will stand up to this better than stainless.
. This involves slowly cooling the steel down to liquid nitrogen
temperatures, leaving it there for a time, and then slowly warming back to room temperature. This process converts remaining austenite
in the steel to martensite
. Many proponents of this process claim increased accuracy of the resulting barrels, but independent testing of the process by major manufacturers has shown no increase in accuracy. However, the conversion of austenite to martensite has been shown to result in easier machining and greater wear resistance on steels that tend to have significant amounts of retained austenite, such as stainless steels, and the process does appear to have a significant impact on the accurate life of stainless steel barrels.
of metal parts during use, and swelling and contracting of wooden stocks with changes in humidity
. These changes can affect accuracy either by allowing the action to shift under recoil, or by causing slight but accuracy-destroying bending of the barrel. By removing wood from areas of contact and, when needed, replacing it with a more stable substance that is precisely fitted, such as a fiberglass composite molded in place, a more stable, precise fit can be achieved. Other materials, such as composites or laminated wood, can also provide a stronger, more dimensionally stables stock than traditional woods can. Some stocks are even being made out of aluminum or other metals, for maximum stability.
The process of fitting the action to the stock is called bedding
, and there are a number of different processes used. Glass bedding uses a fiberglass composite which is molded in place around the action. This can be as simple as bedding the recoil lug of a bolt action rifle, or as complex as bedding the entire action and barrel channel. Pillar bedding uses precisely machined metal pillars in the stock which mate with the action, providing a strong metal-to-metal contact without the labor intensive hand fitting required in glass bedding.
Many times it is advantageous to eliminate most or all contact between the stock and barrel, to eliminate potential accuracy-destroying interference in the barrel harmonics. To do this, stock material is removed along the barrel channel to leave a slight gap between the stock and the barrel; this is called free floating
the barrel. With some designs, pressure bedding is preferred, where a single point of contact remains between stock and barrel near the forend. In both these cases, bedding the action is required to provide support for the floating or pressure bedded barrel. Since the action ends up supporting the mass of the barrel, a poor stock to action fit will result in unacceptable shifting.
are holding the cartridge in place in the chamber, and providing a way to ignite the propellant. In a single-shot
action, little additional functionality is provided, while in a semi-automatic firearm
the action also taps energy from the firing process for cycling to fire the next round. From an accuracy perspective, the primary goal of the action is to achieve a consistent placement of the cartridge in the chamber every shot.
The term blueprinting, borrowed from high performance engine builders, is also often applied to the process of manufacturing or altering parts to a tighter tolerance than stock parts. Blueprinting a firearm action involves similar operations designed to tighten the tolerances of a firearm action to ensure consistent and correct seating of the cartridge in the chamber. A typical set of blueprinting operations for a bolt action firearm would include the following:
These operations ensure that not only is the cartridge consistently and correctly positioned when chambered, but also that it remains correctly positioned during firing.
is the revolving cylinder, separate from the barrel, that contains the chambers. Revolvers typically have 5 to 9 chambers, and the first issue is ensuring consistency among the chambers, because if they aren't consistent then the point of impact will vary from chamber to chamber. The chambers must also align consistently with the barrel, so the bullet enters the barrel the same way from each chamber.
The throat in a revolver is part of the cylinder, and like any other chamber, the throat should be sized so that it is concentric to the chamber and very slightly over the bullet diameter. At the end of the throat, however, things change. First, the throat in a revolver is at least as long as the maximum overall length of the cartridge; if otherwise the cylinder cannot revolve. The next step is the cylinder gap, the space between the cylinder and barrel. This must be wide enough to allow free rotation of the cylinder even when it becomes fouled with powder residue, but not so large that excess gas can be released. The next step is the forcing cone. The forcing cone is where the bullet is guided from the cylinder into the bore of the barrel. It should be concentric with the bore, and deep enough to force the bullet into the bore without significant deformation. Unlike rifles, where the threaded portion of the barrel is in the chamber, revolver barrels threads surround the breech end of the bore, and it is possible that the bore will be compressed when the barrel is screwed into the frame. Cutting a longer forcing cone can relieve this "choke" point, as can lapping of the barrel after it is fitted to the frame.
A consistent lockup is important to keep all these parts in line, and revolvers are prone to abuse that can damage these parts, adversely affecting the accuracy and even safety of the revolver. This lockup consists of two parts, the crane to frame lockup, and the cylinder bolt to cylinder lockup. Many swing-out cylinder revolvers only support the cylinder securely at the rear, and flipping the cylinder open and closed can bend the crane and prevent the cylinder from lining up parallel to the bore. The cylinder bolt, which engages the bottom of the cylinder through a slot in the frame, should provide a relatively tight lockup, and not drag the cylinder during rotation or pop loose when the hammer is cocked at a reasonable speed. Fanning
a revolver can batter the cylinder bolt and prevent a solid lockup.
During firing, the chamber pressure rises from atmospheric pressure to, in a typical rifle cartridge, pressures of about 50,000 psi within milliseconds. This rapid increase in pressure causes the barrel to vibrate at a certain natural frequency
, much like a tuning fork
. The point in time at which the bullet exits the barrel will determine the orientation of the muzzle relative to its rest position. Exiting near a peak or valley in the motion means the muzzle is relatively stationary, and shot dispersion will be minimized; exiting between a peak and valley means the muzzle is rapidly moving, and shot dispersion will be greater.
There are two ways to address harmonics; reducing the amplitude with a stiffer barrel, or working with the natural frequency to minimize dispersion.
barrels, where weight is of very little consequence, have very large diameters; an outside diameter of 2 inches (5 cm) is not uncommon.
While standard rifle barrels taper from breech to muzzle, high precision rifles will often use a barrel with far less taper, called a heavy barrel, sometimes leaving the barrel cylindrical all the way to the muzzle, called a bull barrel. Either technique greatly increases the stiffness of the barrel by enlarging the average diameter, but this process adds significant weight as well. This can greatly increase the mass of the barrel, however; going from a lightweight sporter contour to a heavy barrel contour can double the mass, and a going to a bull barrel contour can more than triple it. Fluting, consisting of grooves machined in the outer surface of the barrel to remove material, can reduce the weight and improve heat dispersion while maintaining most of the stiffness.
Barrel tensioning devices are a way of gaining stiffness with minimal increases in weight. They do this by placing a lightweight sleeve, often made of aluminium or a carbon fiber
composite, around the barrel, and then using a nut attached to the end of the barrel to tension the barrel and place the sleeve under compression. This serves to keep the muzzle closer to concentric and coaxial to the breech during vibration.
of a given cartridge will determine its dwell time, or the time it takes from ignition to exiting the barrel. By experimentally matching the dwell time to the barrel's frequency, the best load for a particular firearm may be found. Similarly, handloading
gives the shooter the opportunity to very precisely control the bullet velocity, and experimentally choose the optimum velocity.
If it is not possible or desirable to match the bullet to the barrel, there are a number of devices marketed to allow the barrel to be tuned to match the ammunition. There are a number of models of these that work in different ways. One type uses an adjustable damper or pressure bedding point to allow the shooter to find the "sweet spot", where it will do the most good at damping the vibrations that are affecting accuracy. Other tuners work by using an adjustable weight on the muzzle to alter the length of the resonant portion of the barrel, and allowing the frequency to be matched to the ammunition.
(CO2). These gases are used primarily for convenience, some airgun variants run on other gases, such as refrigerant
s like R-134a
commonly used in airsoft
guns, or hydrogen
used in light gas gun
s.
There are three primary types of powerplant used in airguns:
Each method has its own advantages and disadvantages, and different areas that can be addressed to ensure consistency.
With recent advances in airgun technology, the most powerful systems will produce velocities near or exceeding the speed of sound
with lightweight pellets; this, however, is not a good thing where accuracy is concerned. Pellets have a poor ballistic coefficient
, and quickly lose velocity; when they drop below the speed of sound, they will often tumble. However, high velocities sell airguns; if accuracy is desired from these high velocity guns, then heavier pellets should be used to keep the velocity down. This will provide not only better accuracy, but better downrange retention of velocity and power.
A single stroke system, as the name implies, uses a single stroke of the pump to compress a cylinder full of air, which is then all used for one shot of the gun. Single stroke systems are both inexpensive and capable of high accuracy due to the simplicity and consistency of the single stroke design. The downsides are the low power provided, though this is not a handicap in standard 10 meter airgun target shooting. When Daisy
introduced an inexpensive single stroke pistol, the model 717, in the late 1970s, American Olympic
shooter Don Nygord demonstrated the potential of the design by shooting an accurized version in a California State air pistol championship, and winning the gold medal. The (at the time) US$40 Daisy, with a better rear sight and an adjustable trigger added, shot as well as the US$400 Olympic class air pistols it was competing against.
More powerful is the pump system, which is a slightly more complex version of the single stroke design. Rather than leaving the air in the piston when compressed, the pump airgun has a reservoir to contain the compressed air, allowing multiple pumps to be used, typically 2 at a minimum, up to 10 pumps for full power. The ability to vary the power, however, it's the pump airgun's major disadvantage when it comes to accuracy, as it makes it very difficult to get a consistent charge. The increased power of a pump airgun makes it an attractive choice for many shooters, and there are steps that can be taken to improve consistency, such as modifying the air chamber so that not all the air is exhausted in a shot.
The last type of pneumatic airgun is the precharged pneumatic. This is both an old and a new design; some of the earliest airguns, such as the model carried by Lewis and Clark, were of this type, as are many new cutting edge models. The precharged pneumatic uses an external source of compressed air, either an external pump or a high pressure reservoir such as a SCUBA tank
, to fill a reservoir. The reservoir can be a small single shot one, such as in the Brocock Air Cartridge system, or a large, multi-shot tank. The key to top accuracy in a precharged pneumatic is a consistent pressure. With multishot systems (as are most), the pressure in the reservoir will drop with each shot fired, so the best way to achieve consistency is with a pressure regulator
, which provides a steady, but lower, pressure at the valve, for as long as the reservoir pressure remains higher than the regulated pressure. Regulators are also generally adjustable, so a low pressure setting will provide many shots of lower power, while a high pressure setting will provide a few high power shots.
The first step to accuracy of a piston gun is to ensure that all screws are secure and the sights are rated for use on a piston airgun. Another potential issue regarding accuracy is resonance in the spring used to power the piston in most airguns. The spring will vibrate strongly as the piston stops, and this will impact the harmonics of the gun. A gas spring
will, if one can be fitted to a given model, provide vibrationless action, though with some loss of efficiency and even sharper recoil. Spring driven pistons also respond well to accurizing; careful fitting of parts and use of quality lubricants and spring damping tar can reduce the level of vibrations and improve accuracy
, as long as there is liquid remaining in the reservoir. The downside to CO2 is that it is dependent upon the vapor pressure, which changes significantly with temperature. This is of primary concern to outdoor shooters, who may shoot in widely varying temperatures, or for rapid fire shooters, as rapid release of the gas results in a rapid drop in the temperature of the liquid.
The issue of temperature change is not readily addressable, other than by the use of readily adjustable sights, so the shooter can adjust the sights to match the point of impact based on the current ambient conditions. In the case of rapid fire, there is a solution that can provide far greater stability for many guns. The original CO2 airguns were filled from an external source of CO2, but in 1954 Crosman
introduced the 12 gram Powerlet
, a compact, disposable tank now ubiquitous in inexpensive CO2 airguns. The downside to these is that the small quantity of CO2 liquid cools down quickly, leading to a rapid drop in velocity and a changing point of impact. By moving to a bulk fill system, with a much larger tank, there is more liquid available, and the greater mass will cool far more slowly.
Firearm
A firearm is a weapon that launches one, or many, projectile at high velocity through confined burning of a propellant. This subsonic burning process is technically known as deflagration, as opposed to supersonic combustion known as a detonation. In older firearms, the propellant was typically...
or airgun.
For firearms, accuracy is defined as the ability to hit exactly what one is aiming at. Further, accuracy and precision
Accuracy and precision
In the fields of science, engineering, industry and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual value. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which...
, or the ability to hit the same place over and over again in a repeatable fashion, are the goals of accurizing.
Accurizing generally concentrates on four different areas:
- Usability: Enhancements that give the shooter a more consistent hold on the firearm, and a more consistent trigger pull.
- Tolerances: Parts that fit together better will shift less or shift more consistently under recoil. Moving parts still have to move, however, and finding the right compromise is more art than science.
- Harmonics: Barrels vibrate under the shock of firing. These vibrations can be minimized or tuned to minimize their impact on accuracy. Generally the harmonic effects are proportional to the square of the barrel length, and so are generally only of concern in rifleRifleA rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile , imparting spin around an axis corresponding to the...
s but not handgunHandgunA handgun is a firearm designed to be held and operated by one hand. This characteristic differentiates handguns as a general class of firearms from long guns such as rifles and shotguns ....
s. - Projectile propulsion consistency: Unlike firearms, airguns provide the propulsive force themselves, instead of relying on the ammunition as firearms do, the source of this power is open to accurizing operations along with the bullet itself. Consistent ammunition performance is extremely critical for accuracy with firearms, as well. While some manufacturers produce match-grade ammo, it is common for high-precision shooters to handload their own ammo.
The key to an accurate firearm is consistency. Getting everything to happen the same way for every shot is key to producing small groups, and there are a large number of issues to be addressed in achieving an accurate firearm. The keys to firing an accurate shot are a firm but not overtight grip, the ability to get a good sight picture, and a controlled squeeze of the trigger. The ability to manage recoil is also important in heavily recoiling calibers, both to aid in possible additional shots, and to prevent the user from developing a fear of the recoil.
Determining accuracy
Determining accuracy is not always a straightforward task, as it depends on a large number of variables.Measurements
Since adjusting the point of impact to match the point of aim is relatively simple with any type of adjustable sights, the primary goal of accurizing is to increase the precision of the firearm, which is generally measured by looking at the dispersion of a number of shots fired at the same point of aim. An ideal group would be one where all shots land in a hole no larger than the diameter of a single bullet; this would indicate zero dispersion. The most common way of measuring groups then is to measure the edge to edge distance of the farthest holes, and subtract the bullet diameter, which gives the center to center or c-t-c measurement of the group. This can be expressed in linear measures (a one inch group at 100 yards) or in angular measures (a MOAMinute of arc
A minute of arc, arcminute, or minute of angle , is a unit of angular measurement equal to one sixtieth of one degree. In turn, a second of arc or arcsecond is one sixtieth of one minute of arc....
group). Groups for rifles are traditionally shot at 100 yards, where a minute of arc equals just over one inch, and the one MOA group is a traditional benchmark
Benchmarking
Benchmarking is the process of comparing one's business processes and performance metrics to industry bests and/or best practices from other industries. Dimensions typically measured are quality, time and cost...
of accuracy. Handguns are generally used at closer ranges, and are tested for accuracy at their intended range of use. Also of importance is the number of shots fired. Statistical likelihood says the fewer shots that are fired, the smaller the dispersion will be. 3 or 5-shot groups are acceptable for zeroing the sights and rough accuracy estimates, but most shooters consider 10-shot groups to be the minimum for accuracy comparisons.
Defining accuracy
Even defining accuracy can be problematic. An example of this can be shown by the following tests, run by Performance Shooter magazine in December, 1996. The magazine was testing seven brands of .38 Special.38 Special
The .38 Smith & Wesson Special is a rimmed, centerfire cartridge designed by Smith & Wesson. It is most commonly used in revolvers, although some semi-automatic pistols and carbines also use this round...
wadcutter
Wadcutter
A wadcutter is a special-purpose bullet specially designed for shooting paper targets, usually at close range and at subsonic velocities typically under 800 ft/s . They are often used in handgun and airgun competitions...
rounds in three different revolver
Revolver
A revolver is a repeating firearm that has a cylinder containing multiple chambers and at least one barrel for firing. The first revolver ever made was built by Elisha Collier in 1818. The percussion cap revolver was invented by Samuel Colt in 1836. This weapon became known as the Colt Paterson...
s, a Smith & Wesson
Smith & Wesson
Smith & Wesson is the largest manufacturer of handguns in the United States. The corporate headquarters is in Springfield, Massachusetts. Founded in 1852, Smith & Wesson's pistols and revolvers have become standard issue to police and armed forces throughout the world...
Model 686 and Model 52, and a Colt Python
Colt Python
The Colt Python is a .357 Magnum caliber revolver formerly manufactured by Colt's Manufacturing Company of Hartford, Connecticut. It is sometimes referred to as a "Combat Magnum". It was first introduced in 1955, the same year as Smith & Wesson's M29 .44 Magnum. The now discontinued Colt Python...
Target model, with six, five and eight inch long barrels, respectively. Ten groups of five shots were fired and measured from each revolver with each ammunition. Click on the image at right to see a larger view of the graph of average group sizes for each type of ammunition and each revolver. The average group size for the overall test was 2.85 inches (72.4 mm).
Based on average
Average
In mathematics, an average, or central tendency of a data set is a measure of the "middle" value of the data set. Average is one form of central tendency. Not all central tendencies should be considered definitions of average....
group size, the winner was the Model 686, which shot an average group of 2.69 inches across the brands of ammunition, with a standard deviation between ammunition types of 0.54 inches. However, the Model 52, while shooting slightly larger groups at 2.88 inches, was far more consistent across the brands, with a standard deviation
Standard deviation
Standard deviation is a widely used measure of variability or diversity used in statistics and probability theory. It shows how much variation or "dispersion" there is from the average...
of only 0.30 inches, and was the most consistent performer of the test. But, if you were able to tune your ammunition to the gun, the clear winner was the Python, which averaged just 1.69 inches with its favored brand of ammunition. The Python was also by far the pickiest, however, turning in the largest groups at 6.08 inch and 4.0 inch averages with its least favorite brands, for a standard deviation of 1.6 inches.
Based on this test, answering the question "Which is the most accurate?" becomes a matter of opinion. The answer that would most likely be given would probably be the 686, as it shot the best average groups. However, as the Python showed the best performance with one brand of ammunition, it might be the best choice if that brand of ammunition were acceptable for the application in question. If a consistent supply of ammunition were a problem, then the 52 might be the best choice, since it showed the least sensitivity to differences in ammunition.
Testing methodology
As the goal of accurizing a firearm is to improve its accuracy, the way accuracy is measured becomes important. A firearm used primarily as a hunting weaponHunting weapon
Hunting weapons are weapons designed or used primarily for hunting game animals for food or sport, as distinct from defensive weapons or weapons used primarily in warfare.-Characteristics:...
will need to be accurate on the first shot from a cold, clean barrel, while one used for target shooting may be allowed fouling shots before the first shot for record is fired. Issues of portability or restrictions of certain competitions may limit the alterations that can be made. In addition, every firearm is different, and processes that yield huge results on one may have no impact on another
Another issue in measuring accuracy is the position in which the shots are fired. The most accurate shooting position is a supported position, such as firing from a benchrest with the firearm well supported by a shooting rest or sandbags; this eliminates much of the shooter's potential for error and will generally result in much smaller groups than firing from an unsupported position. Even for a firearm that is going to be shot offhand, accuracy testing from a machine rest will provide an idea of the ultimate attainable accuracy.
Factors affecting accuracy
The accuracy of a shot relies on many different factors, which can be broken down into three broad categories: the firearm, the cartridge, and the shooter. Accurizing generally refers to the processes that are applied to the firearm. Techniques relating to producing accurate ammunition are covered in internalInternal ballistics
Internal ballistics, a subfield of ballistics, is the study of a projectile's behavior from the time its propellant's igniter is initiated until it exits the gun barrel...
and external ballistics
External ballistics
External ballistics is the part of the science of ballistics that deals with the behaviour of a non-powered projectile in flight. External ballistics is frequently associated with firearms, and deals with the behaviour of the bullet after it exits the barrel and before it hits the target.-Forces...
, and handloading
Handloading
Handloading or reloading is the process of loading firearm cartridges or shotgun shells by assembling the individual components , rather than purchasing completely assembled, factory-loaded cartridges...
, and just like accurizing a firearm, the goal is to produce the most consistent possible results. The shooter must also be consistent, and this means that the fundamentals of marksmanship have to be followed rigorously; any failure on the part of the shooter to remain focused and consistent can result in a bad shot. It's common to use a benchrest or a vise when evaluating ammo or a weapon for accuracy in order to eliminate human error.
Usability
No matter what the potential accuracy of a firearm, it cannot be fired accurately unless the shooter can fire it accurately. A firearm that is comfortable, fits the user well, and provides for a careful, consistent trigger pull and recoil management is not only a physical advantage over a poorly fit firearm, but a psychological one as well.Trigger
The dynamics of the trigger, known as its pull, are one of the most important aspects of usability, since any movement of the firearm caused by pulling the trigger can have an impact on the placement of the shot. Trigger pulls are relative, however. Compare a sport like action shootingAction shooting
Action shooting is a term that encompasses target shooting events where the shooter's score is based on both the accuracy and elapsed time. Disciplines covered by the term include:*United States Practical Shooting Association...
, which emphasizes speed and uses relatively close targets with large scoring zones on the targets, to bullseye
Bullseye (shooting competition)
Bullseye, also known as conventional pistol, is a shooting sport in which participants shoot handguns at paper targets at fixed distances and time limits. A number of organizations, including the NRA and Civilian Marksmanship Program in the United States, have established rules and keep records for...
shooting, which uses distant targets with tiny scoring zones. While both types of trigger need a predictable pull, bullseye shooters demand a much higher degree of precision.
Analysis of the trigger pull
The trigger pull consists of three stages:- takeup or pretravel, which is the movement of the trigger which happens before the searSear (firearm)In a firearm, the sear is the part of the trigger mechanism which holds the hammer or striker back until the correct amount of pressure has been applied to the trigger; at which point the hammer or striker is released to discharge the weapon...
moves - break, the movement during which the trigger moves the sear to the point of release
- overtravel, which is the distance a trigger moves after the sear releases
The takeup is the least critical stage of the trigger pull, and individual preferences vary widely. Two stage triggers, for example, consist of a noticeable takeup, followed by a distinct increase in the force required to pull the trigger, followed by the break. A single stage trigger, on the other hand, has no discernible movement before the break. Fully adjustable triggers will provide a two stage pull, and the option of reducing the first stage travel to zero, essentially making the trigger a single stage trigger.
The break is a far more critical stage of the pull, as it happens just prior to the shot being fired. Here again, individual preferences vary; some shooters prefer a soft break, where there is a smooth but discernible amount of trigger travel during firing, while others prefer a crisp break, with a heavier weight and little or no discernible movement.
The overtravel can be the most critical factor in the trigger pull, as any movement caused at this point will happen as the shot is fired. This is especially important with firearms where there is a sudden release of resistance when the sear breaks, such as in double action triggers. An overtravel stop will arrest the motion of the trigger just after the break, and prevent movement.
Improving the trigger pull
An adjustable trigger may have ways to adjust all of these stages, plus trigger location. For example, a first stage or takeup adjustment might include weight and travel, a second stage or sear engagement adjustment might include weight and travel, and a trigger stop adjustment would limit the overtravel.While adjustable triggers may provide the greatest level of control, much can be done with standard non-adjustable triggers. Careful hand fitting and polishing of parts, addition of high precision or adjustable aftermarket parts, or fabrication of new parts can greatly improve most triggers. Care should be taken, however, since trigger work requires a great deal of care and precision, and a bad trigger job can easily render a firearm highly unsafe or unusable.
Liability issues
Most manufacturers ship firearms with fairly heavy, nonadjustable triggers, colloquially known as lawyer triggers. This is out of concern for liability; firearms are inherently dangerous, and allowing the user to adjust the trigger, or even implying such adjustments can be made, exposes the manufacturer to lawsuit. Likewise, manufacturers of aftermarket parts expose themselves to similar liability issues.Sights
Adjustable sights are essential for most target shooting, as they allow the point of impact to be adjusted to fall in the middle of the target when variables such as target range and ammunition type vary. Firearms with sights that are non-adjustable, or only coarsely adjustable, will not be able to reliably center the point of impact on the target. In addition, good visibility and a crisp sight picture help the user use the sights more reliably.
Typical rifle hunting sights, consisting of a square blade or bead front sight and an open notch mounted in front of the action, are good for quick alignment, but are far from ideal for precision shooting. An aperture sight mounted on the receiver or tang of the rifle, closer to the shooter's eye, will provide a much longer sight radius, which improves the shooter's ability to precisely align the sights. These sights often provide far more precise and repeatable adjustments than stock open sights. Telescopic and reflex sights offer advantages to shooters with poorer eyesight, as they bring the target and reticle into the same plane of focus, as well as providing the option of magnification. The downside to these is the additional weight and bulk they add.
Stocks and grips
A good stockStock (firearm)
A stock, also known as a buttstock or shoulder stock, is a part of a rifle or other firearm, to which the barrel and firing mechanism are attached, that is held against one's shoulder when firing the gun. Stocks are also found on crossbows though a crossbow stock is more properly referred to as a...
or grip is one that allows the shooter to have a relaxed but firm grip on the firearm. This can range from minor changes such as texturing grip surfaces or adding a wide, beavertail type grip safety to a 1911, all the way to a custom built, anatomically designed grip that "fits like a glove". Key features are:
- Structure. A firearm that is properly affixed to the stock, allowing the barrel to float freely as opposed to touching other surfaces, will be more accurate. A stock should also allow the action to be affixed securely and provide a good bedding surface, which sometimes requires the use of epoxy resins.
- Comfort. This allows the shooter to relax and concentrate on shooting.
- Control. The shooter must be able to hold the firearm on target, and provide consistent movement under recoil.
- Positioning. The shooter must be positioned correctly and consistently, allowing easy use of the sights, and a clean trigger pull.
Gripping surfaces
Gripping surfaces, particularly on handguns, are often designed to provide a large degree of friction to prevent the shooter's grip from shifting. This can be done by either using a material that provides a high friction, such as rubberRubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
, or by adding texture to the grips. Traditionally wood grips and stocks are provided with checkering, a process where "V" shaped grooves are cut into the wood at an angle to each other, leaving a pattern of pyramidal projections in the wood. Another process uses a punch to leave a random pattern of dents in the surface, called stippling; this process is better suited to complex curves than checkering, and is often found on anatomical grips. Handguns with plastic frames will often have stippling or checkering molded into the frame.
Handgun grips
Grips for handguns, especially ones used in single handed disciplines such as bullseye and Olympic handgun shooting, are critical to good accuracy. The grip provides very little control compared to a rifle stock, and so a good fit is required to give the shooter control over the gun and isolate the trigger finger movement. Fortunately, aftermarket parts makers provide a wide range of grips for handguns, allowing shooters to find grips that are suitable for their hands.Competition handgun grips are anatomically shaped, and are often custom fitted to the shooter's hand. An ideal grip will fit the contours of the shooter's grip, so that the knuckles fall into position the same way every time. The ideal grip should allow the shooter to repeatedly grasp the gun, bring it up to shooting position with eyes closed, and be correctly aligned and on target when they eyes are opened; this means the grip provides a consistent placement, and minimal corrections when aiming. Contrary to commonly stated rules of thumb, the handgun should not line up with the forearm when gripped, but rather point slightly outwards, so that when held to shoot, the sights line up with the shooter's eye. In cross-dominant shooters, the angle will be more pronounced. Thumbrests, finger grooves (if well fitted), and palm rests all provide control over recoil. An adjustable palm rest is a desirable feature as well, as it allows the grip to be adjusted to fit the shooter's hand as it swells and contracts over time.
Rifle and shotgun stocks
Stocks for long guns are not as often changed as handgun grips, but a well fitted stock can make a significant difference in accuracy. In shotguns in particular, the placement of the shooter's face on the stock provides the rear aiming point, and the correct drop and cast-off can greatly enhance accuracy. This was traditionally accomplished by steaming and bending the stock, but a simpler solution for modern guns is a set of shims that alter the angle of the stock.Rifle stocks have similar issues of fit, and though the use of sights makes this less vital than in a shotgun, a good fit still helps the shooter to relax and concentrate on fundamentals. The shape of a rifle stock should be suited to its intended use. High combs and vertical pistol grips are ideal for high mounted target sights or scopes and careful, deliberate shooting such as encountered in traditional target shooting, metallic silhouette
Metallic silhouette
Metallic silhouette shooting is a group of target shooting disciplines that involves shooting at metal cutouts representing game animals at varying distances. Metallic silhouette shooting can be done with airguns, black powder firearms, modern handguns, or modern rifles...
, or varmint hunting
Varmint rifle
Varmint rifle is an American English term for a small-caliber firearm or high-powered air gun primarily used for varmint hunting — killing non-native or non-game animals such as rats, house sparrows, starling, crows, ground squirrels, gophers, jackrabbits, marmots, groundhogs, porcupine,...
, as they provide a maximum point blank range and ideal trigger control. However, these features are not well suited for a typical hunting or action shooting
Action shooting
Action shooting is a term that encompasses target shooting events where the shooter's score is based on both the accuracy and elapsed time. Disciplines covered by the term include:*United States Practical Shooting Association...
rifle, where the rifle must be brought from a ready position to a shooting position quickly and smoothly. This use favors low sights or scopes, and a shallow pistol grip angle. Rounded forearms are well suited for firing from offhand, while a square-bottomed forearm provides a stable base for shooting off of a sandbag or other rest.
Recoil is also a key issue in rifle stock design. Heavy recoiling rifles should have wide butts, with a good recoil pad to absorb the force of recoil, and a comb that is straight or slopes down towards the action, so that it does not push into the shooter's face under recoil. Other features of target or varmint stocks, such as thumbhole grips, can actually injure the shooter if used in a heavy recoiling hunting rifle.
Some target shooting disciplines allow the use of various devices to help support the rifle, and these are often mounted to an accessory rail beneath the forend. Target slings, unlike carrying slings, are used just on the off hand, usually with a hand stop, and provide stability to the shooter's hold. Palm rests are another device that can be attached to the rail, to allow a shooter to lower their off hand and place their elbow into their body for support. Target stocks also are available with a large degree of adjustment, including length of pull, drop, comb height and angle, and buttplate angle and curvature.
Time considerations
The bullet does not leave the barrel as soon as the sear releases, rather there is a delay between the release of the sear and the bullet exiting the barrel. During this time any movement can move the firearm off target, and so this time should be minimized, especially for firearms that will be fired from an unsupported standing position. This delay can be broken down into two sections, the lock time and the bullet dwell time.Lock time
Lock time is the time between the release of the sear, and the ignition of the cartridge. A lengthy lock time gives time for the shooter to drift off target, and so it is advantageous to minimize the lock time, and reduce the window for error. Reductions in lock time are generally performed by lightening parts that move as part of the firing operation, such as the hammerHammer (firearm)
thumb|150px|Hammer with an integral [[firing pin]] on a [[S&W Model 13]] revolver The hammer of a firearm was given its name for both resemblance and functional similarity to the common tool...
and firing pin or striker
Firing pin
A firing pin or striker is part of the firing mechanism used in a firearm or explosive device e.g. an M14 landmine or bomb fuze. Firing pins may take many forms, though the types used in landmines, bombs, grenade fuzes or other single-use devices generally have a sharpened point...
, and using a more powerful spring. Further reductions in lock time, to near zero levels, can be achieved with electrical primers.
Bullet dwell time
The bullet dwell time is the time between cartridge ignition, and the time the bullet leaves the barrel. Like lock time, dwell time is a window for error, and can be minimized with a faster bullet or a shorter barrel. In some cases a shorter barrel is desired to reduce dwell time, but without losing the sight radius of a longer barrel. In this case a sight extension tube, or bloop tube can be used. This is a tube that fits on the muzzle end of the barrel, providing support for the front sight, but that is bored to much larger than bore diameter. This provides the sight plane of a long barrel with less weight and dwell time.Tolerances
To ensure consistent, repeatable lockup, tolerances between moving partsMoving parts
The moving parts of a machine are those parts of it that move. Machines comprise both moving and fixed parts. The moving parts have controlled and constrained motions....
must be kept to a minimum. This can be achieved by carefully hand selecting parts, and fitting them together. The best fits are generally attained by selecting slightly oversized parts (or altering stock parts to form an interference fit
Interference fit
An interference fit, also known as a press fit or friction fit, is a fastening between two parts which is achieved by friction after the parts are pushed together, rather than by any other means of fastening...
) and then lapping
Lapping
Lapping is a machining operation, in which two surfaces are rubbed together with an abrasive between them, by hand movement or by way of a machine.This can take two forms...
the mating surfaces to attain the desired fit. Tolerances cannot be too tight, however, or functionality will be compromised; this is very important in automatic
Automatic firearm
An automatic firearm is a firearm that loads another round mechanically after the first round has been fired.The term can be used to refer to semi-automatic firearms, which fire one shot per single pull of the trigger , or fully automatic firearms, which will continue to load and fire ammunition...
and semi-automatic firearm
Semi-automatic firearm
A semi-automatic, or self-loading firearm is a weapon which performs all steps necessary to prepare the weapon to fire again after firing—assuming cartridges remain in the weapon's feed device or magazine...
s, where there is a certain amount of energy extracted from the firing of the cartridge that must be used to cycle the action. Overly tight tolerances mean that there is no place for lubricant and dirt to be, and this can bind the parts.
In some cases, stock parts are not sufficient for the task of producing a finished product with sufficiently tight tolerances. In this case, it may be necessary to use specially fabricated parts, built either with minimal tolerances, or parts that are oversized and intended for hand fitting.
Barrel
Bore
Ideally, the bore must be cylindrical and the rifling geometry precisely the same down the length of the bore.A slight gain in the rifling twist, or a slight tapering down of the bore, will still ensure the tight fit of bullet to bore, so when selecting a barrel, the tighter or faster twist end should be chosen for the muzzle.
The twist of the rifling must match the intended ammunition for best accuracy. Rifling with too slow a twist will not stabilize long bullets, causing them to precess in flight; at its worst, this can result in the bullets tumbling in-flight and keyholing, where bullets strike the target sideways. Too fast a twist can also be a problem, as it can magnify problems in the bullet. A bullet whose center of mass is slightly off-center will diverge at a rate proportional to the rifling twist, so excess twist will result in greater dispersion. In practical terms, this is only a problem for rifles chambered for common military calibers where a variety of different loads exist. For example, M-16A1 rifle is unable to accurately fire bullets that are heavier than 55gr due to barrel twist that is too slow to stabilize heavier bullets. Precision rifles typically come with barrels that are either tailor-made for a specific ammo load or made according to the buyer's specifications.
Barrels can also benefit from lapping
Lapping
Lapping is a machining operation, in which two surfaces are rubbed together with an abrasive between them, by hand movement or by way of a machine.This can take two forms...
, not only because it makes the bore a more consistent diameter, but also because it polishes the bore. Barrel lapping should be done with the tool moving in the same direction as the bullet will move, so that any imperfections in the barrel will be smoothed so that they don't interfere with the passage of the bullet. A smooth, polished bore will not only hold the bullet better, but also reduce barrel fouling.
Chamber
Of great importance to accuracy is the fit of the ammunition to the barrel. The chamber should be concentric, and the throat sized just slightly larger than the bullet diameter. The cartridge must headspace correctly, be held firmly in place, concentric to the bore, and the bullet must fit the bore and be guided to engage the riflingRifling
Rifling is the process of making helical grooves in the barrel of a gun or firearm, which imparts a spin to a projectile around its long axis...
cleanly. Once the bullet is engaged in the rifling, with a good seal and coaxial fit, it must stay that way. It is often possible to shorten a barrel slightly by removing material from the breech end and re-cut the chamber, which can correct many problems in the original chamber.
Crown
The crown is the muzzle face of the barrel. The crown's integrity is critical for two reasons:- It is the last part of the firearm touched by the bullet before it exits.
- As the bullet clears the crown, it will release upwards of 5,000-10,000+ PSI of back pressure, which must be as uniform as possible.
While many barrel manufacturers recess the crown to protect it from accidental damage, it can still be damaged over time by cleaning rods that are too hard. It is also not uncommon for factory crowns to be cut slightly off-center, so that one side of the bullet exits slightly earlier than the other, and this will result in the bullet being pushed away from that side, causing a significant deflection in its path. A crown may be re-cut with relative ease, and this can fix any problems caused by a defective or damaged crown, by ensuring an even release of the bullet.
Stress
Any machining process on a barrel, whether it's boring, rifling, or turning the outside contour, will produce some stress in the steel of the barrel. This stress can cause the barrel to expand unevenly as it heats, causing shots to "walk" as the barrel heats and cools. To prevent this, careful post-machining heat treatment is often used to stress-relieveAnnealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
the barrels. The amount of good this does depends on the technique used to make the barrel; the hammer forging method of manufacture, a fast method commonly used by large manufacturers, leaves a significant amount of stress in the barrels, which could be addressed through stress-relieving heat treatment.
Wear
Barrel wear is also an important issue, particularly in high powered firearms. High temperatures tend to erode the barrel at the throat, preventing the bullet from entering the rifling cleanly. One way to produce a long lasting barrel is by the proper selection of materials. Stainless steelStainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
s, such as 416, have been shown to have a longer life than the traditional 4140 chrome
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
/molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
steels used for barrels. While the stainless barrels are not any more accurate than a 4140 barrel, they will maintain their accuracy longer in many applications, as they are more resistant to erosion caused by the heat of firing high powered cartridges. One notable exception to this is the .50 BMG
.50 BMG
The .50 Browning Machine Gun or 12.7×99mm NATO is a cartridge developed for the Browning .50 caliber machine gun in the late 1910s. Entering service officially in 1921, the round is based on a greatly scaled-up .30-06 cartridge...
cartridge; competition shooters often fire high precision lathe
Lathe
A lathe is a machine tool which rotates the workpiece on its axis to perform various operations such as cutting, sanding, knurling, drilling, or deformation with tools that are applied to the workpiece to create an object which has symmetry about an axis of rotation.Lathes are used in woodturning,...
turned bullets made from harder brass, bronze, or steel in this caliber, and the 4140 steel will stand up to this better than stainless.
Cryogenic treatment
Another commonly cited accurizing treatment for barrels is cryogenic treatmentCryogenic hardening
Cryogenic hardening is a cryogenic heat treating process where the material is cooled to approximately , usually using liquid nitrogen. It can have a profound effect on the mechanical properties of certain steels, provided their composition and prior heat treatment are such that they retain some...
. This involves slowly cooling the steel down to liquid nitrogen
Liquid nitrogen
Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...
temperatures, leaving it there for a time, and then slowly warming back to room temperature. This process converts remaining austenite
Austenite
Austenite, also known as gamma phase iron, is a metallic non-magnetic allotrope of iron or a solid solution of iron, with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of ; other alloys of steel have different eutectoid temperatures...
in the steel to martensite
Martensite
Martensite, named after the German metallurgist Adolf Martens , most commonly refers to a very hard form of steel crystalline structure, but it can also refer to any crystal structure that is formed by displacive transformation. It includes a class of hard minerals occurring as lath- or...
. Many proponents of this process claim increased accuracy of the resulting barrels, but independent testing of the process by major manufacturers has shown no increase in accuracy. However, the conversion of austenite to martensite has been shown to result in easier machining and greater wear resistance on steels that tend to have significant amounts of retained austenite, such as stainless steels, and the process does appear to have a significant impact on the accurate life of stainless steel barrels.
Rifle stocks
A poor fit of the action to the stock is also a source of problems, and this problem is exacerbated by issues such as thermal expansionThermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
of metal parts during use, and swelling and contracting of wooden stocks with changes in humidity
Humidity
Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...
. These changes can affect accuracy either by allowing the action to shift under recoil, or by causing slight but accuracy-destroying bending of the barrel. By removing wood from areas of contact and, when needed, replacing it with a more stable substance that is precisely fitted, such as a fiberglass composite molded in place, a more stable, precise fit can be achieved. Other materials, such as composites or laminated wood, can also provide a stronger, more dimensionally stables stock than traditional woods can. Some stocks are even being made out of aluminum or other metals, for maximum stability.
Rifle bedding
Rifle bedding is the process of filling gaps between the action and the stock of a rifle with an epoxy based material. The bedding creates a stable and precise fit for the contact surfaces...
, and there are a number of different processes used. Glass bedding uses a fiberglass composite which is molded in place around the action. This can be as simple as bedding the recoil lug of a bolt action rifle, or as complex as bedding the entire action and barrel channel. Pillar bedding uses precisely machined metal pillars in the stock which mate with the action, providing a strong metal-to-metal contact without the labor intensive hand fitting required in glass bedding.
Many times it is advantageous to eliminate most or all contact between the stock and barrel, to eliminate potential accuracy-destroying interference in the barrel harmonics. To do this, stock material is removed along the barrel channel to leave a slight gap between the stock and the barrel; this is called free floating
Free-floating barrel
A free-floating barrel is a specific design technology used in highly accurate rifles, particularly match grade rifles, to increase the accuracy of the weapon.With normal rifles, the barrel rests in contact with the stock...
the barrel. With some designs, pressure bedding is preferred, where a single point of contact remains between stock and barrel near the forend. In both these cases, bedding the action is required to provide support for the floating or pressure bedded barrel. Since the action ends up supporting the mass of the barrel, a poor stock to action fit will result in unacceptable shifting.
Action
The primary purposes of the firearm actionFirearm action
In firearms terminology, an action is the physical mechanism that manipulates cartridges and/or seals the breech. The term is also used to describe the method in which cartridges are loaded, locked, and extracted from the mechanism. Actions are generally categorized by the type of mechanism used...
are holding the cartridge in place in the chamber, and providing a way to ignite the propellant. In a single-shot
Single-shot
Single-shot firearms are firearms that hold only a single round of ammunition, and must be reloaded after each shot. The history of firearms began with single-shot designs, and many centuries passed before multi-shot designs became commonplace...
action, little additional functionality is provided, while in a semi-automatic firearm
Semi-automatic firearm
A semi-automatic, or self-loading firearm is a weapon which performs all steps necessary to prepare the weapon to fire again after firing—assuming cartridges remain in the weapon's feed device or magazine...
the action also taps energy from the firing process for cycling to fire the next round. From an accuracy perspective, the primary goal of the action is to achieve a consistent placement of the cartridge in the chamber every shot.
The term blueprinting, borrowed from high performance engine builders, is also often applied to the process of manufacturing or altering parts to a tighter tolerance than stock parts. Blueprinting a firearm action involves similar operations designed to tighten the tolerances of a firearm action to ensure consistent and correct seating of the cartridge in the chamber. A typical set of blueprinting operations for a bolt action firearm would include the following:
- Bolt blueprinting operations:
- Squaring the bolt face
- Ensuring the bolt is concentric in the action
- Squaring and lapping the locking lugs
- Sleeving the bolt, then machining down for a precise fit to the action
- Receiver blueprinting operations:
- Making the threads for the barrel concentric
- Making sure the breech face is square to the action centerline
- Making sure the recoil lug is square to the action
- Squaring and lapping the locking lug recesses
These operations ensure that not only is the cartridge consistently and correctly positioned when chambered, but also that it remains correctly positioned during firing.
Revolver specific issues
The defining characteristic of a revolverRevolver
A revolver is a repeating firearm that has a cylinder containing multiple chambers and at least one barrel for firing. The first revolver ever made was built by Elisha Collier in 1818. The percussion cap revolver was invented by Samuel Colt in 1836. This weapon became known as the Colt Paterson...
is the revolving cylinder, separate from the barrel, that contains the chambers. Revolvers typically have 5 to 9 chambers, and the first issue is ensuring consistency among the chambers, because if they aren't consistent then the point of impact will vary from chamber to chamber. The chambers must also align consistently with the barrel, so the bullet enters the barrel the same way from each chamber.
The throat in a revolver is part of the cylinder, and like any other chamber, the throat should be sized so that it is concentric to the chamber and very slightly over the bullet diameter. At the end of the throat, however, things change. First, the throat in a revolver is at least as long as the maximum overall length of the cartridge; if otherwise the cylinder cannot revolve. The next step is the cylinder gap, the space between the cylinder and barrel. This must be wide enough to allow free rotation of the cylinder even when it becomes fouled with powder residue, but not so large that excess gas can be released. The next step is the forcing cone. The forcing cone is where the bullet is guided from the cylinder into the bore of the barrel. It should be concentric with the bore, and deep enough to force the bullet into the bore without significant deformation. Unlike rifles, where the threaded portion of the barrel is in the chamber, revolver barrels threads surround the breech end of the bore, and it is possible that the bore will be compressed when the barrel is screwed into the frame. Cutting a longer forcing cone can relieve this "choke" point, as can lapping of the barrel after it is fitted to the frame.
A consistent lockup is important to keep all these parts in line, and revolvers are prone to abuse that can damage these parts, adversely affecting the accuracy and even safety of the revolver. This lockup consists of two parts, the crane to frame lockup, and the cylinder bolt to cylinder lockup. Many swing-out cylinder revolvers only support the cylinder securely at the rear, and flipping the cylinder open and closed can bend the crane and prevent the cylinder from lining up parallel to the bore. The cylinder bolt, which engages the bottom of the cylinder through a slot in the frame, should provide a relatively tight lockup, and not drag the cylinder during rotation or pop loose when the hammer is cocked at a reasonable speed. Fanning
Fanning (firearms)
Fanning is a revolver shooting technique in which one hand holds the trigger and the other hits the hammer repeatedly. This turns the cylinder and hits the firing pin, in that order, allowing for 'semi-automatic fire' of a revolver...
a revolver can batter the cylinder bolt and prevent a solid lockup.
Harmonics
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
, much like a tuning fork
Tuning fork
A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs formed from a U-shaped bar of elastic metal . It resonates at a specific constant pitch when set vibrating by striking it against a surface or with an object, and emits a pure musical tone after waiting a...
. The point in time at which the bullet exits the barrel will determine the orientation of the muzzle relative to its rest position. Exiting near a peak or valley in the motion means the muzzle is relatively stationary, and shot dispersion will be minimized; exiting between a peak and valley means the muzzle is rapidly moving, and shot dispersion will be greater.
There are two ways to address harmonics; reducing the amplitude with a stiffer barrel, or working with the natural frequency to minimize dispersion.
Stiffness
Stiffness of a barrel is proportional to the fourth power of the diameter, and inversely proportional to the third power of the length. Because of this, short, thick barrels will vibrate with high frequency and low amplitude, and long, thin barrels will vibrate with a low frequency and high amplitude. Due to the impact of length, barrel harmonics are primarily a concern with rifles. By using the shortest and/or fattest barrel possible, the amplitude of the vibrations can be minimized to the point that they are irrelevant to accuracy. Unlimited class benchrest shootingBenchrest shooting
Benchrest shooting is a sport in which very accurate and precise rifles are shot at paper targets from a rest or bench from a sitting position. Benchrest shooters are notoriously detail-oriented and constantly trying to further the accuracy potential of the rifle through experimentation. Nearly...
barrels, where weight is of very little consequence, have very large diameters; an outside diameter of 2 inches (5 cm) is not uncommon.
While standard rifle barrels taper from breech to muzzle, high precision rifles will often use a barrel with far less taper, called a heavy barrel, sometimes leaving the barrel cylindrical all the way to the muzzle, called a bull barrel. Either technique greatly increases the stiffness of the barrel by enlarging the average diameter, but this process adds significant weight as well. This can greatly increase the mass of the barrel, however; going from a lightweight sporter contour to a heavy barrel contour can double the mass, and a going to a bull barrel contour can more than triple it. Fluting, consisting of grooves machined in the outer surface of the barrel to remove material, can reduce the weight and improve heat dispersion while maintaining most of the stiffness.
Barrel tensioning devices are a way of gaining stiffness with minimal increases in weight. They do this by placing a lightweight sleeve, often made of aluminium or a carbon fiber
Carbon fiber
Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...
composite, around the barrel, and then using a nut attached to the end of the barrel to tension the barrel and place the sleeve under compression. This serves to keep the muzzle closer to concentric and coaxial to the breech during vibration.
Harmonic tuning
The other solution is to work with the barrel's natural vibration, and tune the components so that the bullet exits the barrel as it is moving the slowest. The simplest approach to harmonic tuning is to concentrate on the ammunition. The internal ballisticsInternal ballistics
Internal ballistics, a subfield of ballistics, is the study of a projectile's behavior from the time its propellant's igniter is initiated until it exits the gun barrel...
of a given cartridge will determine its dwell time, or the time it takes from ignition to exiting the barrel. By experimentally matching the dwell time to the barrel's frequency, the best load for a particular firearm may be found. Similarly, handloading
Handloading
Handloading or reloading is the process of loading firearm cartridges or shotgun shells by assembling the individual components , rather than purchasing completely assembled, factory-loaded cartridges...
gives the shooter the opportunity to very precisely control the bullet velocity, and experimentally choose the optimum velocity.
If it is not possible or desirable to match the bullet to the barrel, there are a number of devices marketed to allow the barrel to be tuned to match the ammunition. There are a number of models of these that work in different ways. One type uses an adjustable damper or pressure bedding point to allow the shooter to find the "sweet spot", where it will do the most good at damping the vibrations that are affecting accuracy. Other tuners work by using an adjustable weight on the muzzle to alter the length of the resonant portion of the barrel, and allowing the frequency to be matched to the ammunition.
Airgun powerplants
The difference between an airgun and a firearm is the way in which the power to launch the projectile is provided. In a firearm, it is provided by a chemical reaction, and in an airgun is it provided primarily by the expansion of a compressed gas, typically either air or carbon dioxideCarbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2). These gases are used primarily for convenience, some airgun variants run on other gases, such as refrigerant
Refrigerant
A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase change from a liquid to a gas. Traditionally, fluorocarbons, especially chlorofluorocarbons, were used as refrigerants, but they are being phased out because of their ozone depletion...
s like R-134a
1,1,1,2-Tetrafluoroethane
1,1,1,2-Tetrafluoroethane, R-134a, Genetron 134a, Suva 134a or HFC-134a, is a haloalkane refrigerant with thermodynamic properties similar to R-12 , but with less ozone depletion potential...
commonly used in airsoft
Airsoft
Airsoft is a sport in which participants shoot round non-metallic pellets launched via replica firearms.Gameplay varies in style and composition but often range from short-term skirmishes, organized scenarios, military simulations, historical reenactments, to competition target shooting events...
guns, or hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
used in light gas gun
Light gas gun
The light-gas gun is an apparatus for physics experiments, a highly specialized gun designed to generate very high velocities. It is usually used to study high speed impact phenomena , such as the formation of impact craters by meteorites or the erosion of materials by micrometeoroids...
s.
There are three primary types of powerplant used in airguns:
- Pneumatic, which uses pre-compressed air
- Piston, which uses a piston to compress air at the moment of firing
- CO2, which uses a reservoir of liquid carbon dioxide
Each method has its own advantages and disadvantages, and different areas that can be addressed to ensure consistency.
With recent advances in airgun technology, the most powerful systems will produce velocities near or exceeding the speed of sound
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....
with lightweight pellets; this, however, is not a good thing where accuracy is concerned. Pellets have a poor ballistic coefficient
Ballistic coefficient
In ballistics, the ballistic coefficient of a body is a measure of its ability to overcome air resistance in flight. It is inversely proportional to the negative acceleration—a high number indicates a low negative acceleration. BC is a function of mass, diameter, and drag coefficient...
, and quickly lose velocity; when they drop below the speed of sound, they will often tumble. However, high velocities sell airguns; if accuracy is desired from these high velocity guns, then heavier pellets should be used to keep the velocity down. This will provide not only better accuracy, but better downrange retention of velocity and power.
Pneumatic
Pneumatic systems used compressed gas for power, usually compressed air. This air may be compressed by the gun for each shot, in a single stroke or pump (multiple stroke) gun, or it may be precharged by an external compressor.A single stroke system, as the name implies, uses a single stroke of the pump to compress a cylinder full of air, which is then all used for one shot of the gun. Single stroke systems are both inexpensive and capable of high accuracy due to the simplicity and consistency of the single stroke design. The downsides are the low power provided, though this is not a handicap in standard 10 meter airgun target shooting. When Daisy
Daisy Outdoor Products
Daisy is a company that makes and sells inexpensive BB guns and other air guns.-History:Daisy was started in 1882 as Plymouth Iron Windmill Company in Plymouth, Michigan. In 1886 the company started to give BB guns with purchases of windmills. The gun was so popular the company started to sell guns...
introduced an inexpensive single stroke pistol, the model 717, in the late 1970s, American Olympic
Olympic Games
The Olympic Games is a major international event featuring summer and winter sports, in which thousands of athletes participate in a variety of competitions. The Olympic Games have come to be regarded as the world’s foremost sports competition where more than 200 nations participate...
shooter Don Nygord demonstrated the potential of the design by shooting an accurized version in a California State air pistol championship, and winning the gold medal. The (at the time) US$40 Daisy, with a better rear sight and an adjustable trigger added, shot as well as the US$400 Olympic class air pistols it was competing against.
More powerful is the pump system, which is a slightly more complex version of the single stroke design. Rather than leaving the air in the piston when compressed, the pump airgun has a reservoir to contain the compressed air, allowing multiple pumps to be used, typically 2 at a minimum, up to 10 pumps for full power. The ability to vary the power, however, it's the pump airgun's major disadvantage when it comes to accuracy, as it makes it very difficult to get a consistent charge. The increased power of a pump airgun makes it an attractive choice for many shooters, and there are steps that can be taken to improve consistency, such as modifying the air chamber so that not all the air is exhausted in a shot.
The last type of pneumatic airgun is the precharged pneumatic. This is both an old and a new design; some of the earliest airguns, such as the model carried by Lewis and Clark, were of this type, as are many new cutting edge models. The precharged pneumatic uses an external source of compressed air, either an external pump or a high pressure reservoir such as a SCUBA tank
Diving cylinder
A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport high pressure breathing gas as a component of a scuba set. It provides gas to the scuba diver through the demand valve of a diving regulator....
, to fill a reservoir. The reservoir can be a small single shot one, such as in the Brocock Air Cartridge system, or a large, multi-shot tank. The key to top accuracy in a precharged pneumatic is a consistent pressure. With multishot systems (as are most), the pressure in the reservoir will drop with each shot fired, so the best way to achieve consistency is with a pressure regulator
Pressure regulator
A pressure regulator is a valve that automatically cuts off the flow of a liquid or gas at a certain pressure. Regulators are used to allow high-pressure fluid supply lines or tanks to be reduced to safe and/or usable pressures for various applications....
, which provides a steady, but lower, pressure at the valve, for as long as the reservoir pressure remains higher than the regulated pressure. Regulators are also generally adjustable, so a low pressure setting will provide many shots of lower power, while a high pressure setting will provide a few high power shots.
Piston
Piston airguns, often called "springers", are unique in many ways. Since the firing process involves a fairly massive piston suddenly moving to compress the air, they have a significant "kick", generally called "recoil" (though this is not the same as firearm recoil). The recoil begins when the piston starts to move forwards, which pushes the rest of the gun backwards. Then recoil then stops suddenly as the piston reaches the end of its travel, and is brought to a stop by the cushion of high pressure air trapped between the piston and pellet. This recoil can be brutal on the gun in high powered models, and will loosen screws, shift sights, and break scopes not designed specifically for the unique recoil of piston airgun—all of these can lead to poor accuracy. In addition to the recoil, piston airguns have a long lock time, as the piston must compress the air before the pellet begins to move, and the gun is moving due to the recoil during this time. Spring airguns require a special technique to fire, to ensure that the gun moves very consistently during this recoil. The preferred method is a very loose hold, to allow the gun to move back; this means that a piston airgun will not shoot the same from a bench. All accuracy testing and sighting in must be done in the same position the gun will be shot from, otherwise the results will be different. Piston airgun recoil cannot readily be dealt with without a significant redesign; in some cases the action can be mounted on a sliding rail, or two counter-recoiling pistons can be used, but this requires significant changes to the design. The resulting gun will be far less sensitive to the shooter's hold, and thus much easier to shoot accurately.The first step to accuracy of a piston gun is to ensure that all screws are secure and the sights are rated for use on a piston airgun. Another potential issue regarding accuracy is resonance in the spring used to power the piston in most airguns. The spring will vibrate strongly as the piston stops, and this will impact the harmonics of the gun. A gas spring
Gas spring
A gas spring is a type of spring that, unlike a typical metal spring, uses a compressed gas, contained in a cylinder and compressed by a piston, to exert a force. Gas springs are used in automobiles, where they are incorporated into the design of struts that support the weight of hatchback doors...
will, if one can be fitted to a given model, provide vibrationless action, though with some loss of efficiency and even sharper recoil. Spring driven pistons also respond well to accurizing; careful fitting of parts and use of quality lubricants and spring damping tar can reduce the level of vibrations and improve accuracy
CO2
CO2 is commonly found in multishot airguns, from the cheapest plinkers to Olympic class target guns, though the latter are facing competition from regulated precharged pneumatics. CO2's advantage is that it is stored in a liquid form, rather than a gas, and as such provides a greater power density. The liquid also provides a constant pressure, the vapor pressureVapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
, as long as there is liquid remaining in the reservoir. The downside to CO2 is that it is dependent upon the vapor pressure, which changes significantly with temperature. This is of primary concern to outdoor shooters, who may shoot in widely varying temperatures, or for rapid fire shooters, as rapid release of the gas results in a rapid drop in the temperature of the liquid.
The issue of temperature change is not readily addressable, other than by the use of readily adjustable sights, so the shooter can adjust the sights to match the point of impact based on the current ambient conditions. In the case of rapid fire, there is a solution that can provide far greater stability for many guns. The original CO2 airguns were filled from an external source of CO2, but in 1954 Crosman
Crosman
Crosman Corporation is a leading, worldwide designer, manufacturer and supplier of products for the shooting sports. The company has a long standing presence in airgun design and a proud tradition of producing high quality pellet and BB air rifles and pistols...
introduced the 12 gram Powerlet
Powerlet
A Powerlet cartridge is a small disposable metal container holding of liquid CO2 and often a small quantity of oil, used as a power source for certain air guns, paintball markers, and a few airsoft guns...
, a compact, disposable tank now ubiquitous in inexpensive CO2 airguns. The downside to these is that the small quantity of CO2 liquid cools down quickly, leading to a rapid drop in velocity and a changing point of impact. By moving to a bulk fill system, with a much larger tank, there is more liquid available, and the greater mass will cool far more slowly.