A caliber conversion sleeve or adapter sleeve is a device which can be used to non-permanently alter a
firearm to allow it to fire a different
cartridge
Cartridge may refer to:
Objects
* Cartridge (firearms), a type of modern ammunition
* ROM cartridge, a removable component in an electronic device
* Cartridge (respirator), a type of filter used in respirators
Other uses
* Cartridge (surname), a ...
than the one it was originally designed to fire. The different cartridge must be smaller in some dimensions than the original design cartridge, and since smaller cartridges are usually cheaper, the device allows
less expensive fire practice.
Alternative names sometimes imply the type of dimensional difference. A chamber insert may be used for a shorter cartridge of similar base diameter. A supplemental chamber or cartridge adapter is typically used for a shorter cartridge of reduced diameter. A cartridge conversion sleeve may include a short barrel of reduced bore diameter.
Shotgun conversion sleeves may be called subgauge inserts, subgauge tubes, or gauge reducers.
Sleeves intended for
rifle or
handgun cartridges may have rifled barrels. Additional variations may allow
centerfire
Two rounds of .357 Magnum, a centerfire cartridge; notice the circular primer in the center
A centerfire cartridge is a firearm metallic cartridge whose primer is located at the center of the base of its casing (i.e. "case head"). Unlike rim ...
weapons to fire
rimfire ammunition and/or retain autoloading function with the smaller cartridge.
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
The .30-06 Springfield cartridge (pronounced "thirty- aught-six" ), 7.62×63mm in metric notation, and called the .30 Gov't '06 by Winchester, was introduced to the United States Army in 1906 and later standardized; it remained in military use ...
to the shorter
7.62×51mm NATO. Since the chamber insert remains in the chamber, this type of conversion will function in
semi-automatic firearms, and is commonly used in military surplus arms such as the
M1 Garand
The M1 Garand or M1 rifleOfficially designated as U.S. rifle, caliber .30, M1, later simply called Rifle, Caliber .30, M1, also called US Rifle, Cal. .30, M1 is a semi-automatic rifle that was the service rifle of the U.S Army during World War ...
, 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 handgun cartridge to be used in a rifle. These are often called ''supplemental chambers'' or ''cartridge adapters'', 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 of the cartridges must match. The most commonly encountered supplemental chambers are for .30 caliber rifles designed for diameter bullets, to use .32 caliber handgun cartridges with bullet diameters of approximately . Cartridge adapters have also been made to use .38 caliber handgun cartridges with bullet diameters of approximately in .35 caliber rifles designed for bullets of diameter.
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. A notable exception to this is the
Thompson Center Arms
Thompson/Center Arms was an American firearms company based in Springfield, Massachusetts. The company was best known for its line of interchangeable-barrel, single-shot pistols and rifles. Thompson/Center also manufactures muzzle-loading rifl ...
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
rifling 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 open
Break action is a type of firearm action in which the barrel or barrels are hinged much like a door and rotate perpendicularly to the bore axis to expose the breech and allow loading and unloading of cartridges. A separate operation may be requir ...
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 shotguns, 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 shells 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 such as the 12 gauge
X Caliber adapter sleeves.
Automatic firearm conversions
Conversions for
automatic firearms are often more complex than those for single shot or manual repeaters, as the difference in power available to the
operating mechanism can be significant. There are a number of makers of cartridge conversions that convert various centerfire firearms to
.22 Long Rifle
The .22 Long Rifle or simply .22 LR or 22 (metric designation: 5.6×15mmR) is a long-established variety of .22 caliber rimfire ammunition originating from the United States. It is used in a wide range of rifles, pistols, revolvers, smo ...
, operating both as cartridge conversions and caliber conversions.
These conversions typically convert the firearm from
gas operation
Gas-operation is a system of operation used to provide energy to operate locked breech, autoloading firearms. In gas-operation, a portion of high-pressure gas from the cartridge being fired is used to power a mechanism to dispose of the spent ...
or
recoil operation
Recoil operation is an operating mechanism used to implement locked breech, autoloading firearms. Recoil operated firearms use the energy of recoil to cycle the action, as opposed to gas operation or blowback operation using the pressure of the p ...
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
The M1911 (Colt 1911 or Colt Government) is a single-action, recoil-operated, semi-automatic pistol chambered for the .45 ACP cartridge. The pistol's formal U.S. military designation as of 1940 was ''Automatic Pistol, Caliber .45, M1911'' for th ...
,
Glock
Glock is a brand of polymer-Receiver (firearms), framed, Recoil operation#Short recoil operation, short recoil-operated, locked-breech semi-automatic pistols designed and produced by Austrian manufacturer Glock Ges.m.b.H., Glock Ges.m.b.H. The ...
, and
Beretta 92
The Beretta 92 (also Beretta 96 and Beretta 98) is a series of semi-automatic pistols designed and manufactured by Beretta of Italy. The Beretta 92 was designed in 1975, and production began in 1976. Many variants in several different calibers c ...
consist of a new upper assembly and magazine. Conversions for .22 caliber centerfire rifles and carbines such as the
AR-15
An AR-15-style rifle is any lightweight semi-automatic rifle based on the Colt AR-15 design. The original ArmaLite AR-15 is a scaled-down derivative of Eugene Stoner's ArmaLite AR-10 design. The then Fairchild Engine and Airplane Corporatio ...
and
Mini-14
The Mini-14 is a lightweight semi-automatic rifle manufactured by Sturm, Ruger & Co. Introduced in 1973, it is based on the M14 rifle and is essentially a scaled-down version chambered in 5.56×45mm NATO.
It is made in a number of variants, inc ...
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
The AK-47, officially known as the ''Avtomat Kalashnikova'' (; also known as the Kalashnikov or just AK), is a gas-operated assault rifle that is chambered for the 7.62×39mm cartridge. Developed in the Soviet Union by Russian small-arms d ...
or
Thompson submachine gun
The Thompson submachine gun (also known as the "Tommy Gun", "Chicago Typewriter", "Chicago Piano", “Trench Sweeper” or "Trench Broom") is a blowback-operated, air-cooled, magazine-fed selective-fire submachine gun, invented by United Sta ...
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
The .45 ACP ( Automatic Colt Pistol) or .45 Auto (11.43×23mm) is a rimless straight-walled handgun cartridge designed by John Moses Browning in 1904, for use in his prototype Colt semi-automatic pistol. After successful military trials, it ...
version.
One interesting cartridge conversion was the
Pedersen device
The Pedersen device was an experimental weapon attachment for the M1903 Springfield bolt action rifle that allowed it to fire a 7.62 mm caliber, .30 caliber (7.62 mm) pistol-type cartridge in semi-automatic rifle, semi-automatic mode.Military ...
, which was designed to convert the bolt action
Springfield 1903
The M1903 Springfield, officially the United States Rifle, Caliber .30-06, Model 1903, is an American five-round magazine-fed, bolt-action service repeating rifle, used primarily during the first half of the 20th century.
The M1903 was first u ...
Mark I into a 40 shot blowback
semi-automatic firearm chambering a lengthened version of the
.32 ACP
.32 ACP ( Automatic Colt Pistol, also known as .32 Automatic) is a centerfire 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 pi ...
cartridge. The 1903 Mark I differed from the standard rifle in that it had a slot cut in one side of the receiver, which 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 (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
, 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. Potential utility for short range target practice or killing small pests is limited by significantly reduced accuracy of handgun bullets encountering faster rifling twist after gaining velocity in the long jump through the unrifled adapter. Low-powered ammunition, such as the .22 LR, allows the use of indoor ranges or outdoor ranges with smaller downrange impact areas. This can make it possible to conduct training in places where live firing would not be possible (for safety or regulatory reasons) if firing the original full-power ammunition.
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
The .22 CB cap (conical breech cap) is a more powerful version of the .22 BB cap (aka: 6mm Flobert) rimfire metallic cartridge, which was invented by Louis-Nicolas Flobert in 1845. The .22 BB cap and .22 CB cap are interchangeable and are rela ...
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
An air gun or airgun is a gun that fires projectiles pneumatically with compressed air or other gases that are mechanically pressurized ''without'' involving any chemical reactions, in contrast to a firearm, which pressurizes gases ''chem ...
.
An episode of the television series
Columbo[Television episode "Double Exposure" of "Columbo" series. Season 3, Episode 4, originally aired December 16, 1973.] featured a "calibration converter," as it was called in the show. The killer had a large handgun collection in his office but none of them matched the .22 caliber of the bullet he used to kill the victim and Columbo had to figure out what happened to the gun the killer used to commit the crime.
References
External links
MC Ace caliber adaptersShort Lane
{{DEFAULTSORT:Caliber Conversion Sleeve
Pistol and rifle cartridges