Iron sight
Encyclopedia
Sight (device)
A sight is a device used to assist aligning or aim weapons, surveying instruments, or other items by eye. Sights can be a simple set or system of markers that have to be aligned together as well as aligned with the target...
to assist in the aiming of a device such as a firearm
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...
, crossbow
Crossbow
A crossbow is a weapon consisting of a bow mounted on a stock that shoots projectiles, often called bolts or quarrels. The medieval crossbow was called by many names, most of which derived from the word ballista, a torsion engine resembling a crossbow in appearance.Historically, crossbows played a...
, or telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
, and exclude the use of optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
as in telescopic sights
Telescopic sight
A telescopic sight, commonly called a scope, is a sighting device that is based on an optical refracting telescope. They are equipped with some form of graphic image pattern mounted in an optically appropriate position in their optical system to give an accurate aiming point...
or reflector (reflex) sights
Reflector sight
A reflector or reflex sight is a generally non-magnifying optical device that allows the user to look through a partially reflecting glass element and see an illuminated projection of an aiming point or some other image superimposed on the field of view...
. Iron sights are typically composed of two component sights, formed by metal blades: a rear sight mounted perpendicular to the line of sight and consisting of some form of notch (open sight) or aperture (closed sight); and a front sight that is a post, bead, or ring. Civilian
Civilian
A civilian under international humanitarian law is a person who is not a member of his or her country's armed forces or other militia. Civilians are distinct from combatants. They are afforded a degree of legal protection from the effects of war and military occupation...
defensive
Self-defense
Self-defense, self-defence or private defense is a countermeasure that involves defending oneself, one's property or the well-being of another from physical harm. The use of the right of self-defense as a legal justification for the use of force in times of danger is available in many...
, hunting
Hunting
Hunting is the practice of pursuing any living thing, usually wildlife, for food, recreation, or trade. In present-day use, the term refers to lawful hunting, as distinguished from poaching, which is the killing, trapping or capture of the hunted species contrary to applicable law...
, and police
Police
The police is a personification of the state designated to put in practice the enforced law, protect property and reduce civil disorder in civilian matters. Their powers include the legitimized use of force...
firearms usually feature open sights, while many military battle rifle
Battle rifle
A battle rifle is a military service rifle that fires a full power rifle cartridge, such as 7.62x51mm NATO. While the designation of battle rifle is usually given to post-World War II select fire infantry rifles such as the H&K G3, the FN FAL or the M14, this term can also apply to older military...
s employ aperture sights. On many firearms the rear sight is adjustable for elevation
Elevation (ballistics)
In ballistics, the elevation is the angle between the horizontal plane and the direction of the barrel of a gun, mortar or heavy artillery. Originally, elevation was a linear measure of how high the gunners had to physically lift the muzzle of a gun up from the gun carriage to hit targets at a...
or windage
Windage
Windage is a force created on an object by friction when there is relative movement between air and the object.There are two causes of windage:# the object is moving and being slowed by resistance from the air...
.
The earliest and simplest iron sights are fixed and cannot be easily adjusted. Many iron sights are designed to be adjustable, so that the sights can be adjusted for windage and elevation. For precision applications such as hunting
Hunting
Hunting is the practice of pursuing any living thing, usually wildlife, for food, recreation, or trade. In present-day use, the term refers to lawful hunting, as distinguished from poaching, which is the killing, trapping or capture of the hunted species contrary to applicable law...
or sniping
Sniper
A sniper is a marksman who shoots targets from concealed positions or distances exceeding the capabilities of regular personnel. Snipers typically have specialized training and distinct high-precision rifles....
the iron sights are usually replaced by a telescopic sight
Telescopic sight
A telescopic sight, commonly called a scope, is a sighting device that is based on an optical refracting telescope. They are equipped with some form of graphic image pattern mounted in an optically appropriate position in their optical system to give an accurate aiming point...
. Iron sights may still be fitted alongside a telescopic sight
Telescopic sight
A telescopic sight, commonly called a scope, is a sighting device that is based on an optical refracting telescope. They are equipped with some form of graphic image pattern mounted in an optically appropriate position in their optical system to give an accurate aiming point...
and are referred to as Back Up Iron Sights (Acronym B.U.I.S).
Theory
In the case of firearms, where the bulletBullet
A bullet is a projectile propelled by a firearm, sling, or air gun. Bullets do not normally contain explosives, but damage the intended target by impact and penetration...
follows a Newtonian trajectory
Trajectory
A trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...
, front and rear sights must be aligned with the line of sight of the shooter, calibrated to the distance of the target and the trajectory of the bullet, so that the bullet hits the target. Iron sights provide horizontal and vertical reference points that allow the shooter to train the weapon.
Rear sights are usually mounted in a dovetail
Dovetail joint
A dovetail joint or simply dovetail is a joint technique most commonly used in woodworking joinery. Noted for its resistance to being pulled apart , the dovetail joint is commonly used to join the sides of a drawer to the front....
on the barrel
Gun barrel
A gun barrel is the tube, usually metal, through which a controlled explosion or rapid expansion of gases are released in order to propel a projectile out of the end at a high velocity....
or receiver
Receiver (firearms)
In firearms terminology, the receiver is the part of a firearm that houses the operating parts. The receiver usually contains the bolt carrier group, trigger group, and magazine port. In most handguns, the receiver, or frame, holds the magazine well or rotary magazine as well as the trigger mechanism...
, closer to the eye of the shooter, allowing for easy visual
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
pick-up of the notch. Front sights are mounted to the barrel by dovetailing, sweat soldering, screwing, or staking close to the muzzle
Muzzle (firearm)
The muzzle of a firearm is the end of the barrel from which the projectile will exit.Precise machining of the muzzle is crucial to accuracy, because it is the last point of contact between the barrel and the projectile...
, frequently on a ramp
Ramp
- Science and technology :* Inclined plane, a simple machine* Wheelchair ramp, an alternative to stairs* Ramp function, in mathematics the integral of the unit step function* Receptor activity-modifying protein , a class of protein...
. Some front sight assemblies include a detachable hood intended to reduce glare
Glare (vision)
Glare is difficulty seeing in the presence of bright light such as direct or reflected sunlight or artificial light such as car headlamps at night. Because of this, some cars include mirrors with automatic anti-glare functions....
.
With typical blade iron sights, the shooter should center the front post in the notch of the rear sight and the tops of both sights should be level.
Since the eye is only capable of focusing on one plane, and the rear sight, front sight, and target are all in separate planes, only one of those three planes can be in focus. Which plane is in focus depends on the type of sight, and one of the challenges to a shooter is to keep the focus on the correct plane to allow for best sight alignment.
Even a tiny error in the angle of sight alignment results in a trajectory that diverges from the target on a trajectory directly relative to the distance from the target, causing the bullet to miss the target; for example with an 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...
10 metre air rifle shooter trying to hit the 10 ring, which is merely a 0.5 mm diameter dot on the target at 10 meters and with a 4.5 mm diameter pellet
Pellet (air gun)
An air gun pellet is, for the most part, a non-spherical projectile designed to be fired from an air gun. But this is not always the case.Pellets differ from bullets used in firearms because of the pressures encountered; firearms operate at pressures of thousands of atmospheres, while airguns...
, an error of only 0.2 mm in sight alignment can mean a complete miss (a 3 mm point of impact miss). At 1,000 meters, that same 0.2 mm misalignment would be magnified 100 times, giving an error of over 300 mm (1500 times the sight misalignment of 0.2 mm). (Calculations assume a 660 mm sight radius or sighting line)
A long sighting line helps to reduce eventual angle errors and will, in case the sight has an incremental adjustment mechanism, adjust in smaller increments when compared to a further identical shorter sighting line.
Sights for shotguns used for shooting small, moving targets (wing shooting or clay shooting) work quite differently. The rear sight is completely discarded, and the rear reference point is provided by the correct and consistent positioning of the shooter's head. A brightly colored (generally brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...
or silver colored, white, or a fluorescent shade) round bead is placed at the end of the barrel
Gun barrel
A gun barrel is the tube, usually metal, through which a controlled explosion or rapid expansion of gases are released in order to propel a projectile out of the end at a high velocity....
. Often this bead will be placed along a raised, flat rib, which is usually ventilated to keep it cool and reduce mirage
Mirage
A mirage is a naturally occurring optical phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky. The word comes to English via the French mirage, from the Latin mirare, meaning "to look at, to wonder at"...
effects from a hot barrel. Rather than being aimed like a rifle or handgun, the shotgun is pointed—the focus is always on the target, and the unfocused image of the barrel and bead are placed below the target (the amount below depends on whether the target is rising or falling) and slightly ahead of the target if there is lateral movement. This method of aiming is not as precise as that of a front sight/rear sight combination, but it is much faster, and the wide spread of shot allows a hit even if there is some error in aim. Some shotguns also provide a mid-bead, which is a smaller bead located halfway down the rib, which allows more feedback on barrel alignment.
Fixed sights
The earliest and simplest iron sights are fixed and cannot be easily adjusted for variables such as targetBullseye (target)
The bullseye, or bull's-eye, is the centre of a target , and by extension the name given to any shot that hits the bullseye...
distance
Distance
Distance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, or an estimation based on other criteria . In mathematics, a distance function or metric is a generalization of the concept of physical distance...
, the effect of wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
, or variations between different cartridges
Cartridge (firearms)
A cartridge, also called a round, packages the bullet, gunpowder and primer into a single metallic case precisely made to fit the firing chamber of a firearm. The primer is a small charge of impact-sensitive chemical that may be located at the center of the case head or at its rim . Electrically...
. For instance, on many 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, the rear sight consists of a groove milled into the top of the gun's receiver. However, many supposedly "non-adjustable" sights can actually be adjusted, for example the rear sight can often be drifted to compensate for windage if it is mounted in a dovetail, or the rear sight or channel mentioned above can be filed on one side to alter its alignment with the front sight. In other cases the front sight can be very carefully bent to offset it to one side, filed down, or the blade can be replaced with one of a different height. Any of the aforementioned techniques will result in a successful change to the firearm's point of impact, however in taxing situations such as these the services of a gunsmith
Gunsmith
A gunsmith is a person who repairs, modifies, designs, or builds firearms. This occupation is different from an armorer. The armorer primarily maintains weapons and limited repairs involving parts replacement and possibly work involving accurization...
would be well advised.
Adjustable sights
Bullet
A bullet is a projectile propelled by a firearm, sling, or air gun. Bullets do not normally contain explosives, but damage the intended target by impact and penetration...
weight
Weight
In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...
s or propellant loadings, which alter the round's velocity
Velocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
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 thus its trajectory and point of impact.
Sight adjustments are orthogonal, so the windage can be adjusted without impacting the elevation, and vice versa. If the firearm is held canted instead of level when fired, the adjustments are no longer orthogonal, so it is essential to keep the firearm level for best accuracy.
The most common is a rear sight that adjusts in both directions, though military rifles often have a tangent sight in the rear, which a slider on the rear sight has pre-calibrated elevation adjustments for different ranges. With tangent sights, the rear sight is often used to adjust the elevation, and the front the windage. The M16A2 later M16 series rifles have a dial adjustable range calibrated rear sight, and use an elevation adjustable front sight to "zero" the rifle at a given range. The rear sight is used for windage adjustment and to change the zero range.
Types of sights
Iron sights are broken into two basic categories that include most types. Open sights use a notch of some sort as the rear sight, while aperture sights use a circular hole. Wing and clay-shooting shotgun sights are called shotgun beads, or simply beads.Open sights
Open sights generally are used where the rear sight is at significant distance from the shooter's eye. They provide minimum occlusion of the shooter's view, but at the expense of precision. Open sights generally use either a square post or a bead on a post for a front sight. The post or bead is placed in the rear sight notch, and the target is placed above and centered on the aligned sights. From the shooter's point of view, there should be a noticeable space between each side of the front sight and the edges of the notch; the spaces are called light bars, and the brightness of the light bars provides the shooter feedback as to the alignment of the post in the notch. Vertical alignment is done by lining up the top of the front post with the top of the rear sight, or by placing the bead just above the bottom of the V or U-notch. If the post is not centered in the V or U notch, the shot will not be accurate. If the post extends over the V or U-notch it will result in a high shot. If the post does not reach the top of the V or U-notch it will result in a low shot.Patridge sights consisting of a square or rectangular post and a flat-bottomed square notch are the most common form of open sights and are preferred for target shooting, as the majority of shooters find the vertical alignment is more precise than other open sights. V-notch and U-notch sights are a variant of the patridge which substitute a 'V' or 'U' shaped rear notch.
Other common open sight types include the buckhorn, semi-buckhorn, and express. Buckhorn sights have extensions protruding from either side of the rear sight forming a large ring which almost meets directly above the 'V' of the notch. The semi-buckhorn is similar but has a wider gently curving notch with the more precise 'V' at its center and is standard on classic Winchester
Winchester Repeating Arms Company
The Winchester Repeating Arms Company was a prominent American maker of repeating firearms, located in New Haven, Connecticut. The Winchester brand is today used under license by two subsidiaries of the Herstal Group, Fabrique Nationale of Belgium and the Browning Arms Company of Morgan, Utah.-...
and Marlin
Marlin Firearms
Marlin Firearms Co., formerly of North Haven, Connecticut, is a manufacturer of high power, center fire, lever action, and .22 caliber rimfire rifles. In the past, the company made shotguns, derringers and revolvers...
lever-action
Lever-action
Lever-action is a type of firearm action which uses a lever located around the trigger guard area, to load fresh cartridges into the chamber of the barrel when the lever is worked. Most lever-action firearms are rifles, but lever-action shotguns and a few pistols have also been made...
rifles. Express sights are most often used on heavy caliber rifles intended for the hunting of dangerous big game
Big Five game
The phrase Big Five game was coined by white hunters and refers to the five most difficult animals in Africa to hunt on foot. The term is still used in most tourist and wildlife guides that discuss African wildlife safaris. The collection consists of the lion, African elephant, cape buffalo,...
, and are in the form of a wide and large 'V' with a heavy white contrast line marking its bottom and a big white or gold bead front sight. In cases where the range is close and speed far outweighs accuracy (e.g. the shooter is being charged by a Cape Buffalo), the front sight is used like a shotgun bead; the rear sight is ignored, and the bead is placed on the target. When more time is available, the bead is placed in the 'V' of the rear sight.
Advantages and disadvantages
Open sights have many advantages: they are very common, inexpensive to produce, uncomplicated to use, sturdy, lightweight, resistant to severe environmental conditions, and they do not require batteries. On the other hand, they are not as precise as other forms of sights, and are difficult or impossible to adjust. Open sights also take much more time to use—the buckhorn type is the slowest, partridge, 'U' and 'V' type notch sights are only a bit quicker; only the express sight is relatively fast. In addition, open sights tend to block out the lower portion of the shooter's field of viewField of view
The field of view is the extent of the observable world that is seen at any given moment....
by nature, and because of the depth of field
Depth of field
In optics, particularly as it relates to film and photography, depth of field is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image...
limitations of the human eye, do not work as well for shooters with less than perfect vision.
Aperture sights
The image to the right shows a shooter's eye view of the sight picture taken through large and small diameter apertures. The large diameter aperture provides a much brighter image of the target, and the ghosting of the rear ring is evident. The smaller aperture, while providing a much darker image of the target, provides a much greater depth of field (see pinhole camera
Pinhole camera
A pinhole camera is a simple camera without a lens and with a single small aperture – effectively a light-proof box with a small hole in one side. Light from a scene passes through this single point and projects an inverted image on the opposite side of the box...
for an explanation of this effect), yielding a much sharper image of the target.
The theory of operation behind the aperture sight is that the human eye will automatically center the front sight when looked through the rear aperture, thus ensuring accuracy.
These sights are used on target rifle
Rifle
A 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 of several disciplines and on several military rifles such as the M1 Garand
M1 Garand
The M1 Garand , was the first semi-automatic rifle to be generally issued to the infantry of any nation. Called "the greatest battle implement ever devised" by General George S...
, the No. 4 series Enfield
Lee-Enfield
The Lee-Enfield bolt-action, magazine-fed, repeating rifle was the main firearm used by the military forces of the British Empire and Commonwealth during the first half of the 20th century...
s and the M16
M16 rifle
The M16 is the United States military designation for the AR-15 rifle adapted for both semi-automatic and full-automatic fire. Colt purchased the rights to the AR-15 from ArmaLite, and currently uses that designation only for semi-automatic versions of the rifle. The M16 fires the 5.56×45mm NATO...
series of weapons along with several others. Peep sights are very effective in poor lighting, and have found favor with a few hunters who hunt in heavy cover.
Ghost rings
For many shooters, the ghost ring sight is the fastest type of aperture sight. It is fairly accurate, easy to use, and obscures the target less than nearly all other non-optical sights. Because of this, ghost ring sights are commonly installed on combat shotguns and sub-machine guns (and to a much lesser extent, rifles). The ghost ring is a fairly recent innovation, and differs from traditional aperture sights in the extreme thinness of the rear ring, and the slightly thicker front sight. The thin ring minimizes the occlusion of the target, while the thicker front post makes it easy to find quickly.A ghost ring can also take form of a tube ranging from 3–6 cm long, with the post mounted at the inside end of the tube. This type of ghost ring is used when there can be no front sight at the front end of the barrel. It is slightly slower to use, because the shooter's eye has to focus close on the post, then focus on the target. However, in situations when extremely fast sighting is required, the shooter can simply look through the tube, and it is simple to see if the view is straight down the tube.
Target aperture sights
Diopter sight
The diopter is an aperture sight component used to assist the aiming of a guns/devices, usually those intended to launch projectiles, such as firearms, airguns, and crossbows...
) is usually a large disk (up to 1 inch or 2.5 cm in diameter) with a small hole in the middle, and is placed close to the shooter's eye. High end target diopters normally accept accessories like adjustable diopter aperture and optical filter systems to ensure optimal sighting conditions for match shooters. Typical modern target shooting diopters offer windage and elevation corrections in 2 mm (0.078740157480315 in) to 4 mm (0.15748031496063 in) increments at 100 m (109.4 yd). Some ISSF (Olympic) shooting events require this precision level for sighting lines, since the score of the top competitors last 10 shots is expressed in 0.1s of scoring ring points.
The complementing front sight element may be a simple bead or post, but is more often a globe
Globe sight
A globe sight is a front sight component used to assist the aiming of a gun/device, usually those intended to launch projectiles, such as firearms, airguns, and crossbows...
type sight, which consists of a cylinder
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
with a threaded cap, which allows differently shaped removable front sight elements to be used. Most common are posts of varying widths and heights or rings of varying diameter—these can be chosen by the shooter for the best fit to the target being used. Tinted transparent plastic insert elements may also be used, with a hole in the middle; these work the same way as an opaque ring, but provide a less obstructed view of the target. High end target front sight tunnels normally also accept accessories like adjustable aperture and optical systems to ensure optimal sighting conditions for match shooters. Some high end target sight line manufacturers also offer front sights with integrated aperture mechanisms.
The use of round rear and front sighting elements for aiming at round targets, like used in ISSF match shooting, takes advantage of the natural ability of the eye and brain to easily align concentric circles (circles all having a common centre). Even for the maximum precision, there should still be a significant area of white visible around the bullseye and between the front and rear sight ring (if a front ring is being used). Since the best key to determining center is the amount of light passing through the apertures, a narrow, dim ring of light can actually be more difficult to work with than a larger, brighter ring. The precise sizes are quite subjective, and depend on both shooter preference and ambient lighting, which is why target rifles come with easily replaceable front sight inserts, and adjustable aperture mechanisms.
Rifles from the late 19th century often featured one of two types of aperture sight called a tang sight or a ladder sight. Since the black powder used in muzzleloader
Muzzleloader
A muzzleloader is any firearm into which the projectile and usually the propellant charge is loaded from the muzzle of the gun . This is distinct from the more popular modern designs of breech-loading firearms...
s and early cartridges was not capable of propelling a bullet at high velocity, these sights had very large ranges of vertical adjustments, often on the order of several degrees, allowing very long shots to be made accurately. The .45-70
.45-70
The .45-70 rifle cartridge, also known as .45-70 Government, was developed at the U.S. Army's Springfield Armory for use in the Springfield Model 1873...
cartridge, for example, was tested by the military for accuracy at ranges of up to 1500 yards, which required 3 1/3 degrees of elevation. Both ladder and tang sights folded down when not in use to reduce the chance of damage to the sights. Ladder sights were mounted on the barrel, and could be used as sights in both the folded and unfolded states. Tang sights were mounted behind the action of the rifle, and provided a very long sight radius, and had to be unfolded for use, though rifles with tang sights often had open sights as well for close range use. Tang sights often had vernier scale
Vernier scale
A vernier scale is an additional scale which allows a distance or angle measurement to be read more precisely than directly reading a uniformly-divided straight or circular measurement scale...
s, allowing adjustment down to a single minute of arc over the full range of the sight.
Aperture sights on military rifles use a larger aperture with a thinner ring, and generally a simple post front sight. The extreme case of this is the ghost ring sight, a relatively recent innovation that may be the fastest type of iron sight to use, while still providing a degree of precision comparable to or better than most open sights. Ghost ring sights are commonly found on riot
Riot shotgun
A riot shotgun is a shotgun designed or modified for use as a primarily defensive weapon, primarily by the use of a short barrel. The riot shotgun is used by military personnel for guard duty and was at one time used for riot control, and is commonly used as a patrol weapon by law enforcement...
and combat shotgun
Combat shotgun
A combat shotgun is a shotgun that is intended for use in an offensive role, typically by a military force. The earliest shotguns specifically designed for combat were the trench guns or trench shotguns issued in World War I...
s and customized handgun
Handgun
A 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, and they are also gaining ground as a backup sighting system on rifle
Rifle
A 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.
Shotgun beads
Since shotgun beads are only used by the peripheral visionPeripheral vision
Peripheral vision is a part of vision that occurs outside the very center of gaze. There is a broad set of non-central points in the field of view that is included in the notion of peripheral vision...
, generally a larger, brighter bead works best. Fiber optic sights are becoming popular for shotguns, as they greatly increase the brightness of the bead by collecting light and directing it to the shooter's eye. Since the "rear sight" in the case of a shotgun is the shooter's eye position, adjusting the "sights" on a shotgun consists primarily of adjusting the stock to fit the shooter as well as possible.
Bead sights are inferior in practical accuracy compared to rifle and ghost-ring sights, as they provide no rear sight to verify correct alignment with the front sight. While bead sights may be acceptable on sporting shotguns, they are best avoided for use on combat shotguns.
The primary advantage of bead sights is that they do not interfere with the shooter's field of vision, allowing extremely rapid target acquisition, this is essential for fast moving targets such as clays and game. They are less expensive than rifle and ghost-ring sights.
Enhancements
While iron sights are basically very simple, that simplicity also leads to a staggering variety of different implementations. In addition to the purely geometric considerations of the front blade and rear notch, there are some factors that need to be considered when choosing a set of iron sights for a particular purpose.Glare reduction
Glare, particularly from the front sight, can be a significant problem with iron sights. The glare from the front sight can increase the apparent brightness of the light bar on one side of the sight, causing windage errors in aiming, or lower the apparent height of the front sight, causing elevation errors in aiming. Since the direction of the ambient light is rarely constant for a shooter, the resulting changing glare can significantly affect the point of aim.The most common solution to the problem of glare is a matte finish on the sights. Serrating or bead blasting the sight is a common solution for brightly finished sights, such as blued steel or stainless steel. Matte finishes such as parkerizing
Parkerizing
Parkerizing is a method of protecting a steel surface from corrosion and increasing its resistance to wear through the application of an electrochemical phosphate conversion coating...
or matte black paint can also help. "Smoking" a sight by holding a match or cigarette lighter under the sight to deposit a fine layer of soot is a common technique used by many shooters, and in fact special soot producing cigarette type lighters are sold for use by competition shooters. Even a thin layer of mud or dirt applied to the sight will help kill the glare, as long as the coating is thin and consistent enough not to change the shape of the sights.
Many target sights are designed with vertical or even undercut front sight blades, which reduces the angles at which light will produce glare off the sight—the downside of these sights is that they tend to snag on clothing, branches, and other materials, so they are only common on target guns. Sight hoods reduce the chances of snagging an undercut sight and are common on some types of rifles, particularly lever action rifles, but they are prohibited in some shooting disciplines such as some classes of handgun 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...
shooting.
Fixed vs. adjustable sights
The downside to adjustable sights is the inherent fragility of the moving parts. A fixed sight is a solid piece of metal, usually steel, and if firmly attached to the gun, little is going to be able to damage it beyond usefulness. Adjustable sights, on the other hand, are bulkier, and have parts that must move relative to the gun. Solid impact on an adjustable sight will usually knock it out of adjustment, if not knock it right off the gun. Because of this, guns for self defense or military use either have fixed sights, or sights with "wings" on the sides for protection (such as those on the M4 carbine).Iron sights used for hunting guns tend to be a compromise. They will be adjustable, but only with tools—generally either a small screwdriver
Screwdriver
A screwdriver is a tool for driving screws and often rotating other machine elements with the mating drive system. The screwdriver is made up of a head or tip, which engages with a screw, a mechanism to apply torque by rotating the tip, and some way to position and support the screwdriver...
or an allen wrench. They will be compact and heavily built, and designed to lock securely into position. Target sights, on the other hand, are much bulkier and easier to adjust. They generally have large knobs to control horizontal and vertical movement without tools, and often they are designed to be quickly and easily detachable from the gun so they can be stored separately in their own protective case.
Contrast enhancements
Gloss (material appearance)
Gloss is an optical property, which is based on the interaction of light with physical characteristics of a surface. It is actually the ability of a surface to reflect light into the specular direction. The factors that affect gloss are the refractive index of the material, the angle of incident...
black finish to their sights, to reduce the chance of glare and increase the contrast between the sights and the light bars, black sights don't offer good visibility with dark targets or in low light conditions, such as those often encountered in hunting, military, or self defense situations. A variety of different contrast enhancements to the basic Patridge type sight and others have been developed to address this deficiency. It should be noted that the contrast enhancement of the front sight has to be somewhat larger compared to the contrast enhancement(s) used for the rear sight if all contrast enhancements should appear about equally large from the shooters perspective.
- Three-dot: On semi-automatic handguns, the most common type of enhancement is a bright white dot painted on the front sight near the top of the blade, and a dot on each side of the rear sight notch. In low lighting conditions the front sight dot is centered horizontally between the rear sight dots, with the target placed above the middle (front) dot. Some sight vendors offer differently colored dots for the front and rear sights.
- White outline rear: A contrast variation which uses a dot front sight with a thick and bright white outline around the rear sight notch.
- Straight Eight: Heinie Specialty Products produces a variant of high visibility sights in which a single dot front sight and a rear notch with a dot below can be lined up vertically to form a figure "eight".
- Sight inserts: Popular on revolvers, this enhancement consists of a colored plastic insert in the front sight blade, usually red or orange in color.
- Bar/Dot or Express sight: Similar to the Straight Eight type, this type of sight is traditional on express rifleExpress rifleThe term express was first applied to hunting rifles and ammunition beginning in the middle 19th century, to indicate a rifle or ammunition capable of higher than typical velocities. The early express cartridges used a heavy charge of black powder to propel a lightweight, often hollow point...
s and is also found on some handguns. The open, V-shaped rear allows for faster acquisition and wider field of view, though less accurate for longer range precision type shooting. The dot on the front sight is aligned or set directly above the vertical bar on the rear sight, commonly referred to as "dotting the 'I'". - Gold bead: Preferred by many competitors in IPSC and IDPA shooting.
- Night sights: On Tactical firearms, the contrast enhancements can consist of trasers containing tritiumTritiumTritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...
gas, which emit a dim light due to the radioactive decayRadioactive decayRadioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
of the tritium, and fluorescentPhosphorescencePhosphorescence is a specific type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs. The slower time scales of the re-emission are associated with "forbidden" energy state transitions in quantum...
material. Self-luminous tritium sights provide vital visibility in extremely low light situations where normal sights would be degraded or even useless. - Fiber optic: A growing trend, started on air rifles and muzzleloaders, is the use of short pieces of optical fiberOptical fiberAn optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
for the dots, made in such a way that ambient light falling on the length of the fiber is concentrated at the tip, making the dots slightly brighter than the surroundings.This method is most commonly used in front sights, but many makers offer sights that use fiber optics on front and rear sights. Fiber optic sights can now be found on handguns, rifles, and shotguns, both as aftermarket accessories and a growing number of factory guns.
Concealed carry
Specific to handguns is the issue of concealed carry. While police and military personnel generally carry their handguns in open holsters that provide easy and unobstructed access, civilians in areas where concealed carry is allowed, and who choose to carry concealed carry their firearms hidden under clothing or some other form of cover, such as an untucked shirt, fanny pack or purse. The high contrast, sharp edges that are popular with target shooters can be dangerous on a concealed firearm—not only can they tear skin and clothing when drawn, but if they become tangled during the draw, entanglement can have lethal consequences for the shooter.The challenge for a designer of sights for a concealable handgun is to pick the right compromise between high visibility and minimum hindrance. Rather than the vertical or even undercut front sights found on target handguns, the front sights of a concealed carry gun will be sloped. The rear sight will not be a vertical plate, but will have depth to provide a gentle slope, and the sight will fit the gun more closely, with no gaps or overlaps to snag, or to collect dirt and sweat which can cause corrosion.
Design criteria for sights for use on a concealed handgun also have to consider the potential conditions in which they are expected to be used—probably low light, close range, and with the operator under significant stress due to an imminent threat. Some unusual solutions have been devised, such as the trapezoidal sights used by Steyr M (shown as G in Types of Iron Sights), or the "gutter sight" used by the highly modified ASP
ASP (handgun)
The ASP was a custom made handgun designed and built by Paris Theodore, owner of Seventrees, Ltd. a custom gun leather shop in New York from 1975 to 1987. The ASP was based on the Smith & Wesson Model 39 pistol. The ASP featured clear Lexan grips allowing the shooter to see how much ammunition is...
S&W model 39.
Optical sights
For precision applications such as huntingHunting
Hunting is the practice of pursuing any living thing, usually wildlife, for food, recreation, or trade. In present-day use, the term refers to lawful hunting, as distinguished from poaching, which is the killing, trapping or capture of the hunted species contrary to applicable law...
or sniping
Sniper
A sniper is a marksman who shoots targets from concealed positions or distances exceeding the capabilities of regular personnel. Snipers typically have specialized training and distinct high-precision rifles....
the iron sights are usually replaced by a telescopic sight
Telescopic sight
A telescopic sight, commonly called a scope, is a sighting device that is based on an optical refracting telescope. They are equipped with some form of graphic image pattern mounted in an optically appropriate position in their optical system to give an accurate aiming point...
, and for target shooting and combat operations low-power magnified or unmagnified optical sights such as reflector (reflex) sights
Reflector sight
A reflector or reflex sight is a generally non-magnifying optical device that allows the user to look through a partially reflecting glass element and see an illuminated projection of an aiming point or some other image superimposed on the field of view...
are increasingly common. Iron Sights may still be fitted alongside a telescopic sight
Telescopic sight
A telescopic sight, commonly called a scope, is a sighting device that is based on an optical refracting telescope. They are equipped with some form of graphic image pattern mounted in an optically appropriate position in their optical system to give an accurate aiming point...
and are referred to as Back Up Iron Sights (Acronym B.U.I.S), typically BUIS sights fold down when not in use.
Adjusting for accuracy
If the sights are not aligned correctly, then the sights should be adjusted to bring the line of sight to meet the point of impact. Theoretically, this can be done with a single shot—clamp the firearm into a vise, fire one shot, then adjust the sights so they are pointing at the hole in the target. In reality, it generally takes a number of shots to establish a group, then the sights are adjusted to move the line of sight closer to the group, and the process is repeated iteratively until the sights are correctly aligned.The general rule is the rear sight is moved in the SAME direction you wish to move the point of impact. For example, if the point of impact is LEFT and BELOW the target, and you wish to move the point of impact to the center, then move the rear sight RIGHT and UP. The front sight moves the opposite direction, so it would move LEFT and DOWN.
Detailed instructions for adjusting the sights:
- To move the line of sight DOWN (the shot hit BELOW the point of aim) the REAR sight is RAISED or the FRONT sight is LOWERED.
- To move the line of sight UP (the shot hit ABOVE the point of aim) the REAR sight is LOWERED or the FRONT sight is RAISED. (Example below)
- To move the line of sight LEFT (the shot hit LEFT of the point of aim) the REAR sight is moved RIGHT, or the FRONT sight is moved LEFT.
- To move the line of sight RIGHT (the shot hit RIGHT of the point of aim) the REAR sight is moved LEFT, or the FRONT sight is moved RIGHT.
Many target sights have click adjustments, where a detent in the adjustment screws allows the sight to move the line of sight a certain angular distance with each click. This distance is usually specified in minutes of arc
Minute 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....
, which translate to approximately 1 inch at 100 yards. On a firearm with 1 minute clicks, then, it would take 1 click to move 1 inch at 100 yards, 2 clicks to move 1 inch at 50 yards, 4 clicks to move 1 inch at 25 yards. If click adjustments are not available, or the click interval is not known, then the distance to lengthen or shorten the sight for a given point of aim adjustment is:
D1 / R1 = D2 / R2
For rear sight adjustments:
- D1 is the distance between point of aim and point of impact.
- R1 is range from front sight to target.
- D2 is the length the rear sight must change by.
- R2 is the distance between front and rear sights.
For front sight adjustments:
- D1 is the distance between point of aim and point of impact.
- R1 is range from rear sight to target.
- D2 is the length the front sight must change by.
- R2 is the sight radius distance between front and rear sights.
This formula calculates the MAGNITUDE ONLY of the sight height change; refer to the instructions above to find the correct direction for the adjustment (front or rear sight, longer or shorter). Likewise, all distances must be in the same units. That is, if a change in inches to the sight height is desired, and one is shooting on a 100-yard range, then R1 (100 yd) must be converted to inches (100 × 36 = 3600 inches) before using this distance in the equation.
An example: Consider a rifle with a distance between front and rear sights of 26.25 inches, firing on a 50-yard (1800 in) range, with point of impact 5.3 inches too high on the target, having a front sight blade that is 0.505 inches high mounted in a dovetail. How much must the front sight blade height be changed by to fix this problem? (It will be assumed that the muzzle of the rifle intrudes into the range space for following typical gun range safety protocols, and the rear sight is hence 50 yards from the target.)
D2 = R2(D1/R1) = 26.25(5.3/1800) = 0.077" (magnitude of change to front sight height)
Since the gun is hitting too high, the front sight must be lengthened by this much per the instructions cited previously; hence, the front sight must be replaced with a blade that is 0.505" + 0.077" = 0.582" high. With this correction, the rifle will hit the desired point of impact, all other factors being equal.
See also
- List of telescope parts and construction
- Telescopic sightTelescopic sightA telescopic sight, commonly called a scope, is a sighting device that is based on an optical refracting telescope. They are equipped with some form of graphic image pattern mounted in an optically appropriate position in their optical system to give an accurate aiming point...
- Reflex sight
- Laser sight
