Caliber conversion sleeve
Encyclopedia
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...
to allow it to fire a different cartridge
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...
than the one it was originally designed to fire.
Altering cartridge length
The simplest conversion is one that alters the length of the cartridge used, allowing a shorter but otherwise similarly dimensioned cartridge to be fired. Commonly called chamber inserts, these conversions resemble the front of the case, and are inserted into the firearm by placing over the new cartridge and inserting both into the chamber of the firearm. This seats the chamber insert into the front of the chamber, where it remains after firing. Once inserted, the chamber insert will remain in place until removed with the use of a stuck case remover. The most commonly encountered chamber inserts are ones designed to convert .30-06 Springfield.30-06 Springfield
The .30-06 Springfield cartridge or 7.62×63mm in metric notation, was introduced to the United States Army in 1906 and standardized, and was in use until the 1960s and early 1970s. It replaced the .30-03, 6 mm Lee Navy, and .30 US Army...
to the shorter 7.62 x 51 mm NATO. Since the chamber insert remains in the chamber, this type of conversion will function in 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, and is commonly used in military surplus arms 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...
, allowing the use of often less expensive surplus military ammunition.
Altering the cartridge diameter
The next level in complexity involves altering the diameter of the cartridge used, typically allowing a short, straight walled handgunHandgun
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 ....
cartridge to be used in a 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...
. These are often called supplemental chambers, and the entire supplemental chamber is treated like a cartridge, being loaded and ejected as a unit with the smaller cartridge. Since the barrel of the firearm is used, the caliber
Caliber
In guns including firearms, caliber or calibre is the approximate internal diameter of the barrel in relation to the diameter of the projectile used in it....
of the cartridges must match. The most commonly encountered supplemental chambers are for .30 caliber (7.62 mm) rifle cartridges, and use .32 ACP
.32 ACP
.32 ACP , also known as the .32 Automatic is a pistol cartridge. It is a semi-rimmed, straight-walled cartridge developed by firearms designer John Browning, initially for use in the FN M1900 semi-automatic pistol...
or other similarly sized cartridges.
Supplemental chambers in .22 caliber, and potentially .17 caliber as well, pose a special problem not shared by larger calibers. Rimfire cartridges, with their low cost, noise, and recoil, are ideal for use in a supplemental chamber, except for the fact that the firearm in question is almost certainly a centerfire design. This means that supplemental chambers that use a rimfire cartridge must also provide a special offset firing pin. This is a metal insert that fits behind the rimfire cartridge, and has an appropriate projection to act as a firing pin. When this insert is hit by the firearm's firing pin, it is pushed forwards, which causes it to crush the rim of the rimfire cartridge, igniting it. Use of the centerfire to rimfire conversion requires a longer case, and so is not suitable for short cartridges such as .22 Hornet
.22 Hornet
The .22 Hornet is a low-end vermin, small-game and predator centerfire rifle cartridge. It is considerably more powerful than the .22 WMR and the .17 HMR, achieving higher velocity with a bullet twice the weight. The Hornet also differs very significantly from these in that it is not a rimfire...
. A notable exception to this is the Thompson Center Arms
Thompson Center Arms
Thompson/Center Arms Company is an American firearms company based in Rochester, New Hampshire. The company is best known for its line of interchangeable barrel single-shot pistols and rifles. Thompson Center manufactures muzzleloading rifles and is credited with creating the resurgence of their...
Contender, which has both centerfire and rimfire firing pins which can be selected with the turn of a switch, and does not require a centerfire to rimfire converter. The Hammond Game Getter works around this problem in its sleeves for .22 rimfire by creating an eccentric chamber that places the rim of the .22 cartridge in the center of the original chamber, thus allowing the firing pin to strike it directly.
Since the supplemental chambers are approximately the size of a normal loaded cartridge, they will usually feed from a magazine, though they will not provide sufficient energy to cycle an automatic action.
Altering the caliber
The most complete transformation is offered by the caliber conversion sleeve. These include not only a new chamber, but a new barrel as well, allowing a smaller diameter bullet to be fired. These sleeves may be significantly longer than a loaded cartridge, if the length of the parent cartridge is not sufficient to provide the desired performance. Unlike the other types of cartridge conversions, this type incorporates 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...
to stabilize the bullet; the other types rely on the rifling in the firearm's barrel.
Chamber length sleeves
Chamber length sleeves are restricted cases where a short cartridge is used with a long parent cartridge. The sleeve is rifled up to the end of the sleeve. Since most cartridge cases are only a couple of inches long (about 5 cm) this provides limited power. On the other hand, these will function from magazines in the same way as supplemental chambers, and allow the use of the least expensive rimfire ammunition in firearms chambered in calibers larger than .22 (5.56 mm).Greater than chamber length sleeves
Sleeves that exceed the chamber length are generally used in break openBreak open
A break-action firearm is one whose barrels are hinged, and rotate perpendicular to the bore axis to expose the breech and allow loading and unloading of ammunition. A separate operation may be required for the cocking of a hammer to fire the new round...
actions, which allow easy insertion and removal. Like supplemental chambers, caliber conversion sleeves completely surround the new cartridge case, but cannot be ejected or fed from a magazine, so they only offer a single shot per barrel without manual extraction and reloading.
The calibers supported by caliber conversion sleeves are limited by the difference between the calibers. The sleeve's barrel must be thick enough to provide structural integrity to the barrel, and so requires a large enough internal barrel diameter to hold the new barrel. One manufacturer has a .40 caliber (10 mm) minimum diameter for these inserts in .22 rimfire caliber.
Some manufacturers offer caliber conversion sleeves for shotgun
Shotgun
A shotgun is a firearm that is usually designed to be fired from the shoulder, which uses the energy of a fixed shell to fire a number of small spherical pellets called shot, or a solid projectile called a slug...
s, which convert a shotgun into a rifle with the use of a rifled barrel.
Shotguns
Inserts for shotguns are called subgauge inserts, and function in much the same manner as inserts for handguns or rifles. However, due to the nature of shotguns, the implications of using an insert differ.Since shotgun shell
Shotgun shell
A shotgun shell is a self-contained cartridge loaded with lead shot or shotgun slug designed to be fired from a shotgun....
s are all straight walled, a change in chambering means a change in diameter of the shell. However, since subgauge inserts are designed to be used with shot, not slugs, the shotgun's barrel can continue to be used, with little or no impact on patterning. Many makers offer longer inserts, though due to the variations in shotgun bore diameters, these usually require custom manufacture.
Rifled inserts are also available, to allow the use of handgun cartridges or relatively low-power rifle cartridges.
Automatic firearm conversions
Conversions for automatic firearmAutomatic 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...
s are often more complex than those for single shot or manual repeaters, as the difference in power available to the operating mechanism
Firearm 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...
can be significant. There are a number of makers of cartridge conversions that convert various centerfire firearms to .22 Long Rifle
.22 Long Rifle
The .22 Long Rifle rimfire cartridge is a long established variety of ammunition, and in terms of units sold is still by far the most common in the world today. The cartridge is often referred to simply as .22 LR and various rifles, pistols, revolvers, and even some smoothbore shotguns have...
, operating both as cartridge conversions and caliber conversions.
These conversions typically convert the firearm from gas operation or recoil operation
Recoil operation
Recoil operation is an operating mechanism used in locked-breech, autoloading firearms. As the name implies, these actions use the force of recoil to provide energy to cycle the action...
to a simple blowback operation. This typically involves replacing the firearm's bolt or slide with a lightweight part lacking the locking mechanism, and a reduced power spring. The magazine must also be replaced, and in the case of caliber conversions, often the barrel as well. Conversions for short recoil pistols, such as the M1911
M1911
The M1911 is a single-action, semi-automatic, magazine-fed, and recoil-operated handgun chambered for the .45 ACP cartridge. John M. Browning designed the firearm which was the standard-issue side arm for the United States armed forces from 1911 to 1985. The M1911 is still carried by some U.S....
, Glock
Glock
Glock Ges.m.b.H. is a weapons manufacturer headquartered in Deutsch-Wagram, Austria, named after its founder, Gaston Glock...
, and Beretta 92
Beretta 92
The Beretta 92 is a series of semi-automatic pistols designed and manufactured by Beretta of Italy. The model 92 was designed in 1972 and production of many variants in different calibers continues today...
consist of a new upper assembly and magazine. Conversions for .22 caliber centerfire rifles and carbines such as the AR-15
AR-15
The AR-15 is a lightweight, 5.56 mm, air-cooled, gas-operated, magazine-fed semi-automatic rifle, with a rotating-lock bolt, actuated by direct impingement gas operation. It is manufactured with the extensive use of aluminum alloys and synthetic materials....
and Mini-14
Mini-14
The Mini-14, Mini Thirty, and Mini-6.8 are small, lightweight semi-automatic carbines manufactured by the U.S. firearms company Sturm, Ruger. The Mini-14 non-target versions can fire both the .223 Remington cartridge and the similar military 5.56x45mm cartridge. The target model Mini-14 rifles are...
consist of a magazine and an insert that replaces the bolt and includes a cartridge conversion insert that goes into the chamber. Conversions for rifles and carbines of larger caliber, such as the AK-47
AK-47
The AK-47 is a selective-fire, gas-operated 7.62×39mm assault rifle, first developed in the Soviet Union by Mikhail Kalashnikov. It is officially known as Avtomat Kalashnikova . It is also known as a Kalashnikov, an "AK", or in Russian slang, Kalash.Design work on the AK-47 began in the last year...
or Thompson submachine gun
Thompson submachine gun
The Thompson is an American submachine gun, invented by John T. Thompson in 1919, that became infamous during the Prohibition era. It was a common sight in the media of the time, being used by both law enforcement officers and criminals...
include a rifled insert barrel extending beyond the length of the chamber.
One exception to the use of a special lightweight bolt was the Colt Service Ace, offered as a complete pistol or as a conversion kit for the M1911. While still nominally a blowback conversion, the Service Ace used a special "floating" chamber in the barrel that acted like a gas operated firearm's piston, helping push the bolt back with more force than a typical .22 Long Rifle blowback action. This additional force allowed the small .22 Long Rifle cartridge to cycle a standard weight slide, which made the pistol handle more like the standard .45 ACP
.45 ACP
The .45 ACP , also known as the .45 Auto by C.I.P., is a cartridge designed by John Browning in 1904, for use in his prototype Colt semi-automatic .45 pistol and eventually the M1911 pistol adopted by the United States Army in 1911.-Design and history:The U.S...
version.
One interesting cartridge conversion was the Pedersen device
Pedersen device
The Pedersen Device is an attachment developed during World War I for the M1903 Springfield rifle that allowed it to fire a short .30 Caliber intermediate cartridge in semi-automatic mode...
, which was designed to convert the bolt action Springfield 1903 Mark I into a 40 shot blowback submachine gun
Submachine gun
A submachine gun is an automatic carbine, designed to fire pistol cartridges. It combines the automatic fire of a machine gun with the cartridge of a pistol. The submachine gun was invented during World War I , but the apex of its use was during World War II when millions of the weapon type were...
chambering a lengthened version of the .32 ACP
.32 ACP
.32 ACP , also known as the .32 Automatic is a pistol cartridge. It is a semi-rimmed, straight-walled cartridge developed by firearms designer John Browning, initially for use in the FN M1900 semi-automatic pistol...
cartridge. The 1903 Mark I differed from the standard rifle in that had a slot cut in one side of the receiver, which to served as an ejection port for the Pedersen device. The Pedersen device replaced the bolt of the 1903, and loaded from a magazine inserted from the top right of the receiver. Intended as a "secret weapon", the device was not ready for issue before the end of World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
, and it was eventually declared obsolete without being issued, and all but a handful of the devices were destroyed by the military.
Uses
In addition to often being less expensive than the larger cartridge, the smaller cartridges offer much reduced recoil and muzzle blast. They are useful for short range target practice or killing small pests. With shotguns, the smaller shot load carried by a smaller shell increases the challenge of hitting targets, and therefore can be used as a handicap for a skilled shooter, or to increase difficulty when training.Some European conversions exist for special gallery cartridges, similar in concept to the .22 CB
.22 CB
.22 CB Cap is a variety of .22 caliber rimfire ammunition which has a very small propellant charge , resulting in a low muzzle velocity of between 350 and 700 ft/s...
rounds, which use a primer but no gunpowder. These adapters were chambered for centerfire versions of these tiny rounds, such as the 4mm 4mm Übungsmunition cartridge. Gallery cartridges such as these were intended for use in indoor target practice, and are similar in power and report to an airgun.