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Gas-operation is a system of operation used to provide energy to operate
locked breech Locked breech is the design of a breech-reloading firearm's action. This is important in understanding how a self-reloading firearm works. In the simplest terms, the locked breech is one way to slow down the opening of the breech of a self-reloadi ...
, autoloading
firearm A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries (see Legal definitions). The first firearms originated in 10th-century China, when bamboo tubes ...
s. 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 case and insert a new cartridge into the chamber. Energy from the gas is harnessed through either a port in the
barrel A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wooden or metal hoops. The word vat is often used for large containers for liquids, u ...
or a trap at the muzzle. This high-pressure gas impinges on a surface such as a
piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...
head to provide motion for unlocking of the
action Action may refer to: * Action (narrative), a literary mode * Action fiction, a type of genre fiction * Action game, a genre of video game Film * Action film, a genre of film * ''Action'' (1921 film), a film by John Ford * ''Action'' (1980 fil ...
, extraction of the spent case, ejection, cocking of the hammer or striker, chambering of a fresh cartridge, and locking of the action.


History

The first mention of using a gas piston in a single-shot breech-loading rifle comes from 1856, by the German Edward Lindner who patented his invention in the United States and Britain. In 1866, Englishman William Curtis filed the first patent on a gas-operated repeating rifle, but subsequently failed to develop that idea further. Between 1883 and 1885,
Hiram Maxim Sir Hiram Stevens Maxim (5 February 1840 – 24 November 1916) was an American-British inventor best known as the creator of the first automatic machine gun, the Maxim gun. Maxim held patents on numerous mechanical devices such as hair-curl ...
filed a number of patents on blowback-, recoil-, and gas-operation. In 1885, one year after Maxim's first gas-operated patent, a British inventor called Richard Paulson, who a year before had patented a straight blowback-operated rifle and pistol, again, one year after Maxim’s first blowback patent, patented a gas piston-operated rifle and pistol which he claimed could be used with sliding, rotating or falling bolts. He would also patent a gas-operated revolver in 1886. It is not known whether Paulson ever constructed prototypes of his patents but according to A. W. F. Taylerson, a firearms historian, his patented revolver was probably workable. In the 1880s a gas piston-operated rifle and pistol were developed by the Clair Brothers of France who received a French patent and submitted prototypes for testing by the French army in 1888 although the true date of their invention is uncertain. They would also produce a semi-automatic shotgun in the early 1890s. In 1889, the
Austro-Hungarian Austria-Hungary, often referred to as the Austro-Hungarian Empire,, the Dual Monarchy, or Austria, was a constitutional monarchy and great power in Central Europe between 1867 and 1918. It was formed with the Austro-Hungarian Compromise of ...
Adolf Odkolek von Újezd filed a patent for the first successful gas-operated machine gun.


Piston systems

Most current gas systems employ some type of piston. The face of the piston is acted upon by combustion gas from a port in the barrel or a trap at the muzzle. Early guns, such as Browning's "flapper" prototype, the Bang rifle, and Garand rifle, used relatively low-pressure gas from at or near the muzzle. This, combined with larger operating parts, reduced the strain on the mechanism. To simplify and lighten the firearm, gas from nearer the chamber needed to be used. This high-
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and ...
gas has sufficient force to destroy a firearm unless it is regulated somehow. Most gas-operated firearms rely on tuning the gas port size, mass of operating parts, and spring pressures to function. Several other methods are employed to regulate the energy. The
M1 carbine The M1 carbine (formally the United States Carbine, Caliber .30, M1) is a lightweight semi-automatic carbine that was a standard firearm for the U.S. military during World War II, the Korean War and the Vietnam War. The M1 carbine was produced ...
incorporates a very short piston, or "tappet." This movement is closely restricted by a shoulder recess. This mechanism inherently limits the amount of gas taken from the
barrel A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wooden or metal hoops. The word vat is often used for large containers for liquids, u ...
. The
M14 rifle The M14 rifle, officially the United States Rifle, Caliber 7.62 mm, M14, is an American selective fire battle rifle chambered for the 7.62×51mm NATO (.308 in) cartridge. It became the standard-issue rifle for the U.S. military in 1959, re ...
and M60
GPMG A general-purpose machine gun (GPMG) is an air-cooled, usually belt-fed machine gun that can be adapted flexibly to various tactical roles for light and medium machine guns. A GPMG typically features a quick-change barrel design calibered for ...
use the White expansion and cutoff system to stop (cut off) gas from entering the cylinder once the piston has traveled a short distance. Most systems, however, vent excess gas into the atmosphere through slots, holes, or ports.


Gas trap

A gas trap system involves "trapping" combustion gas as it leaves the muzzle. This gas impinges on a surface that converts the energy to motion that, in turn cycles the action of the firearm. As the resulting motion is forward toward the muzzle of the gun, some sort of mechanical system is needed to translate this into the rearward motion needed to operate the bolt. This adds to the complexity of the mechanism and its weight, and the placement of the trap generally results in a longer weapon and allows dirt to easily enter the mechanism. Despite these disadvantages, they used relatively low pressure gas and did not require a hole in the barrel, which made them attractive in early designs. The system is no longer used in modern weapons.
Hiram Maxim Sir Hiram Stevens Maxim (5 February 1840 – 24 November 1916) was an American-British inventor best known as the creator of the first automatic machine gun, the Maxim gun. Maxim held patents on numerous mechanical devices such as hair-curl ...
patented a muzzle-cup system in 1884 described in though it is unknown if this firearm was ever prototyped.
John Browning John Moses Browning (January 23, 1855 – November 26, 1926) was an American firearm designer who developed many varieties of military and civilian firearms, cartridges, and gun mechanisms many of which are still in use around the world. He m ...
used gas trapped at the muzzle to operate a "flapper" in the earliest prototype gas-operated firearm described in , and used a slight variation of this design on the
M1895 Colt–Browning machine gun The Colt–Browning M1895, nicknamed "potato digger" because of its unusual operating mechanism, is an air-cooled, belt-fed, gas-operated machine gun that fires from a closed bolt with a cyclic rate of 450 rounds per minute. Based on an 1889 des ...
"potato digger". The Danish Bang rifle used a muzzle cup blown forward by muzzle gas to operate the action through transfer bars and leverage. Other gas-trap rifles were early production
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 ...
s and German
Gewehr 41 The Gewehr 41 (German for: rifle 41), commonly known as the G41(W) or G41(M), denoting the manufacturer ( Walther or Mauser), are two distinct and different battle rifles manufactured and used by Nazi Germany during World War II. They were lar ...
(both Walther and Mauser models). The American and German governments both had requirements that their guns operated without a hole being drilled in the barrel. Both governments would first adopt weapons and later abandon the concept. Most earlier US M1 Garand rifles were retrofitted with long-stroke gas pistons, making the surviving gas trap rifles valuable in the collector's market.


Long-stroke

With a long-stroke system, the piston is mechanically fixed to the bolt group and moves through the entire operating cycle. This system is used in weapons such as the
Bren light machine gun The Bren gun was a series of light machine guns (LMG) made by Britain in the 1930s and used in various roles until 1992. While best known for its role as the British and Commonwealth forces' primary infantry LMG in World War II, it was also us ...
,
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 de ...
,
Tavor The IWI Tavor TAR-21 is an Israeli bullpup assault rifle chambered in 5.56×45mm NATO caliber with a selective fire system, selecting between semi-automatic mode and full automatic fire mode. The Tavor is designed and produced by Israel Weapo ...
,
FN Minimi The FN Minimi (short for french: Mini Mitrailleuse; "mini machine gun") is a Belgian 5.56mm light machine gun/squad automatic weapon developed by Ernest Vervier for FN Herstal. First introduced in the late 1970s, it is now in service in more tha ...
,
FN MAG The FN MAG is a Belgian 7.62 mm general-purpose machine gun, designed in the early 1950s at Fabrique Nationale (FN) by Ernest Vervier. It has been used by more than 80 countries and it has been made under licence in several countries, in ...
,
FN FNC The FNC (french: Fabrique Nationale Carabine) is a 5.56×45mm NATO assault rifle developed by the Belgian arms manufacturer FN Herstal and introduced in the late 1970s. Development The FNC was developed between 1975–1977 for NATO standardiza ...
, and
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 ...
. The primary advantage of the long-stroke system is that the
mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different eleme ...
of the piston rod adds to the
momentum In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass a ...
of the bolt carrier enabling more positive extraction, ejection, chambering, and locking. The primary disadvantage to this system is the disruption of the point of aim due to several factors such as: the
center of mass In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may ...
changing during the action cycle, abrupt stops at the beginning and end of bolt carrier travel, and the use of the barrel as a fulcrum to drive the bolt back. Also, due to the greater mass of moving parts, more gas is required to operate the system that, in turn, requires larger operating parts.


Short-stroke

With a short-stroke or ''tappet'' system, the piston moves separately from the bolt group. It may directly push the bolt group parts, as in the
M1 carbine The M1 carbine (formally the United States Carbine, Caliber .30, M1) is a lightweight semi-automatic carbine that was a standard firearm for the U.S. military during World War II, the Korean War and the Vietnam War. The M1 carbine was produced ...
, or operate through a connecting rod or assembly, as in the
Armalite AR-18 The ArmaLite AR-18 is a gas-operated assault rifle chambered for 5.56×45mm NATO ammunition. The AR-18 was designed at ArmaLite in California by Arthur Miller, Eugene Stoner, George Sullivan, and Charles Dorchester in 1963 as an alternative t ...
or the SKS. In either case, the energy is imparted in a short, abrupt push and the motion of the gas piston is then arrested allowing the bolt carrier assembly to continue through the operating cycle through
kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its accele ...
. This has the advantage of reducing the total mass of recoiling parts compared with a long-stroke piston. This, in turn, enables better control of the weapon due to less mass needing to be stopped at either end of the bolt carrier travel. This design is available both on the civilian and military markets as retrofit to 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 ...
family of weapons for addressing the shortcomings of the Stoner gas system.


Short-stroke fixed

It is a cross between a short-stroke gas piston and a M1 Garand type long-stroke gas piston system. It is similar to a regular short-stroke piston in operation because it too uses an open gas piston that has an impingement cavity at its head, that rests on a gas block on the barrel. However just like the long-stroke gas piston system used on the M1 Garand the piston assembly is integrated with the operating rod and moves with the bolt group. The caveat of this system is that it has heavier moving mass than modern long-stroke gas piston systems used on rifles like 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 de ...
,
Tavor The IWI Tavor TAR-21 is an Israeli bullpup assault rifle chambered in 5.56×45mm NATO caliber with a selective fire system, selecting between semi-automatic mode and full automatic fire mode. The Tavor is designed and produced by Israel Weapo ...
,
FN FNC The FNC (french: Fabrique Nationale Carabine) is a 5.56×45mm NATO assault rifle developed by the Belgian arms manufacturer FN Herstal and introduced in the late 1970s. Development The FNC was developed between 1975–1977 for NATO standardiza ...
, etc. Hence firearms using this system do have higher felt recoil than their equivalent modern long-stroke gas piston counterparts.


Gas-delayed blowback

The bolt is not locked but is pushed rearward by the expanding
propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the e ...
gases as in other blowback-based designs. However, propellant gases are vented from the barrel into a cylinder with a piston that delays the opening of the bolt. It is used by
Volkssturmgewehr 1-5 The Volkssturmgewehr ("People's Storm - Rifle") is the name of several rifle designs developed by Nazi Germany during the last months of World War II. They share the common characteristic of being greatly simplified as an attempt to cope with se ...
rifle, the
Heckler & Koch P7 The Heckler & Koch P7 is a German 9×19mm semi-automatic pistol designed by Helmut Weldle and produced from 1979 to 2008 by Heckler & Koch GmbH (H&K). It was revealed to the public for the first time in 1976 as the PSP (''Polizei-Selbstlade-Pi ...
,
Steyr GB The Steyr GB is a double-action 9×19mm Parabellum caliber, large-framed semi-automatic pistol employing a gas-delayed blowback action. As such the GB abbreviation stand for ''Gasbremse'' (gas brake). It was designed in 1968, intended as a repl ...
and Walther CCP pistols.


Floating chamber

To avoid consuming a lot of relatively expensive rounds, many armies, including the United States Army, trained machine gun crews with less-expensive sub-caliber ammunition in the late 19th century and the first half of the 20th century. To do this, they needed a cheap
.22 LR 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, smooth ...
cartridge to operate firearms designed to use the .30-06 cartridge.
David Marshall Williams David Marshall Williams (November 13, 1900 – January 8, 1975) was an American firearms designer and convicted murderer who invented the floating chamber and the short-stroke piston. Both designs used the high-pressure gas generated in or near ...
invented a method that involved a separate floating chamber that acted as a gas piston with combustion gas impinging directly on the front of the floating chamber. The .22 caliber Colt Service Ace conversion kit for the .45 caliber
M1911 pistol 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 ...
also used Williams' system, which allows a much heavier slide than other conversions operating on the unaugmented blowback mechanism and makes training with the converted pistol realistic. A floating chamber provides additional force to operate the heavier slide, providing a felt
recoil Recoil (often called knockback, kickback or simply kick) is the rearward thrust generated when a gun is being discharged. In technical terms, the recoil is a result of conservation of momentum, as according to Newton's third law the force re ...
level similar to that of a full power cartridge.


Direct impingement

The
direct impingement Direct impingement is a type of gas operation for a firearm that directs gas from a fired cartridge indirectly (through the barrel, through a gas block, and then through a gas tube) into the bolt carrier or slide assembly to cycle the action. Fi ...
(DI) method of operation vents gas from partway down the barrel through a tube to the working parts of a rifle where they directly impinge on the bolt carrier. This results in a simpler, lighter mechanism. Firearms that use this system include the French MAS-40 from 1940, the Swedish Ag m/42 from 1942. The Stoner gas system of the American M16 series and M4 utilizes a gas tube to directly impinge the bolt carrier, while the USMC's M27 is based on the short piston-driven
HK416 The Heckler & Koch HK416 is a gas-operated assault rifle chambered for the 5.56×45mm NATO cartridge. It is designed and manufactured by the German company Heckler & Koch. Although the design is based on the AR-15 class of firearm (specific ...
. One principal advantage is that the moving parts are placed in-line with the bore axis meaning that sight picture is not disturbed as much. This offers a particular advantage for fully automatic mechanisms. It has the disadvantage of the high-temperature
propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the e ...
gas (and the accompanying fouling) being blown directly into the action parts. Direct impingement operation increases the amount of heat that is deposited in the receiver while firing, which can burn off and cover up lubricants. The bolt, extractor, ejector, pins, and springs are also heated by the same high-temperature gas. These combined factors reduce service life of these parts, reliability, and
mean time between failures Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a mechanical or electronic system during normal system operation. MTBF can be calculated as the arithmetic mean (average) time between failures of a system ...
.Major Thomas P. Ehrhart Increasing Small Arms Lethality in Afghanistan: Taking Back the Infantry Half-Kilometer. US Army. 2009


Other uses of gas in firearms

Several other uses have been found for exhaust gases other than to aid cycling: ;
Muzzle booster A muzzle booster or recoil booster is a device fixed to the muzzle of a firearm, intended to harness the energy of the escaping propellant to augment the force of recoil on portions of the firearm. In spite of its name, a muzzle booster does not ...
: The French
Chauchat The Chauchat ("show-sha", ) was the standard light machine gun or "machine rifle" of the French Army during World War I (1914–18). Its official designation was "Fusil Mitrailleur Modele 1915 CSRG" ("Machine Rifle Model 1915 CSRG"). Beginning ...
, German
MG 34 The MG 34 (shortened from German: ''Maschinengewehr 34'', or "machine gun 34") is a German recoil-operated air-cooled general-purpose machine gun, first tested in 1929, introduced in 1934, and issued to units in 1936. It introduced an entirely n ...
and
MG 42 The MG 42 (shortened from German: ''Maschinengewehr 42'', or "machine gun 42") is a German recoil-operated air-cooled general-purpose machine gun used extensively by the Wehrmacht and the Waffen-SS during the second half of World War II. Ente ...
machine guns, the British
Vickers machine gun The Vickers machine gun or Vickers gun is a water-cooled .303 British (7.7 mm) machine gun produced by Vickers Limited, originally for the British Army. The gun was operated by a three-man crew but typically required more men to move and o ...
, and some other recoil operated firearms use a gas trap style mechanism to provide additional energy to 'boost' the energy provided by recoil. This "boost" provides higher rates of fire and/or more reliable operation. It is alternately called a ''gas assist'', and may also be found in some types of
blank-firing adapter A blank-firing adapter or blank-firing attachment (BFA), sometimes called a blank adapter or blank attachment, is a device used in conjunction with blank ammunition for safety reasons, functional reasons or a combination of them both. Blank firin ...
s. ; Gas ejection: Patented by August Schüler, the Reform pistol featured a vertical row of barrels that advanced upwards with each shot exposing the fired chamber. As the lower barrel fired, a gas hole between the barrels pressurized the empty barrel enough to eject the case rearward. An extended spur on the hammer prevented the spent case from hitting the firer in the face. The final case required manual extraction.


See also

*
Delayed blowback Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gas created by the ignition of the propellant charge. Several blowback systems exist ...
*
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 ...
* Blowback operation *
Blow forward Blow-forward is a firearm action where the propellant gas pressure and the friction of the bullet traveling down the bore drag the whole gun barrel forward to facilitate the opening of the breech. This forward barrel motion provides most of t ...


References

{{Use mdy dates, date=January 2016 Firearm actions