Recoil operation
Encyclopedia
Recoil operation is an operating mechanism used in locked-breech, autoloading firearm
s. As the name implies, these actions use the force of recoil
to provide energy to cycle the action. Other operating systems are Blow forward operated
, blowback operated
, gas operated, gatling
, and chain
.
, etc.) are accelerated down the barrel of a firearm, all or a portion of the firearm will begin to move in the opposite direction, as required for conservation of momentum
, according to the formula:
which is calculated by:
In non-recoil-operated firearms, it is generally the entire firearm that recoils. However, in recoil-operated firearms, only a portion of the firearm recoils while inertia
holds another portion motionless relative to a mass such as the ground, a ship's gun mount, or a human holding the firearm. The moving and the motionless masses are coupled by a spring that absorbs the recoil energy as it is compressed by the movement and then expands providing energy for the rest of the operating cycle.
Since there is a minimum momentum required to operate a recoil-operated firearm's action, the cartridge
must generate sufficient recoil to provide that momentum. Therefore, recoil-operated firearms work best with a cartridge that yields a momentum approximately equal to that for which the mechanism was optimized. For example, the M1911
design with factory springs is optimized for a 230 gr bullet at factory velocity. Changes in caliber or drastic changes in bullet weight and/or velocity require modifications to spring weight or slide mass to compensate.
Long recoil operation is found primarily in shotgun
s, particularly ones based on John Browning
's Auto-5
action. In a long recoil action, the barrel and bolt remain locked together during recoil, compressing the recoil spring or springs. Following this rearward movement, the bolt locks to the rear and the barrel is forced forward by the spring. The bolt is held in position until the barrel returns completely forward during which time the spent cartridge has been extracted and ejected, and a new shell has been positioned from the magazine. The bolt is released and forced closed by its recoil spring, chambering a fresh round.
The long recoil system is over a century old and dominated the automatic shotgun market for more than half that century before it was supplanted by new gas-operated
designs. While Browning halted production of the Auto-5 design in 1999, Franchi
still makes a long-recoil–operated shotgun line, the AL-48
, which shares both the original Browning action design, and the "humpbacked" appearance of the original Auto-5. Other weapons based on the Browning system were the Remington Model 8
semi-automatic rifle (1906), the Remington Model 11 & "The Sportsman" model (a model 11 with only a 2 shell magazine) shotguns, the Frommer Stop
line of pistols (1907) and the Chauchat
machine rifle (1915).
The short recoil action dominates the world of centerfire automatic pistol
s, being found in nearly all such weapons chambered for 9x19mm Parabellum or higher-powered cartridges (weaker cartridges, .380 ACP
and below, generally use the blow-back
method of operation). Short recoil operation differs from long recoil operation in that the barrel and slide recoil together only a short distance before they unlock and separate. The barrel stops quickly, and the slide continues rearward, compressing the recoil spring and performing the automated extraction and feeding process. During the last portion of its forward travel, the slide locks into the barrel and pushes the barrel back into battery.
The exact method of locking and unlocking the barrel is the primary differentiating factor in the wide array of short recoil designs. Most common are the John Browning tilting barrel designs, based either on the swinging link and locking lugs as used in the M1911 pistol, or the linkless cam design used in the Hi Power
. Other common designs are the locking block design found in the Beretta 92
, rollers in the MG42
, or a rotating barrel used in the Steyr TMP
among others. One unusual variant is the 1890 toggle bolt
design of Hugo Borchardt
, used in the German
Luger pistol
.
While the short recoil design is most common in pistols, the very first short-recoil–operated firearm was also the first machine gun
, the Maxim gun
. It used a toggle bolt similar to the one Borchardt later adapted to pistols. Vladimirov also used the short recoil principle in the Soviet KPV-14.5
heavy machine gun which has been in service with the russian military and middle eastern armed forces for 80 years. Melvin Johnson also used the short recoil principle in his M1941 rifle & M1944 light machine gun.
, or use a design licensed from Benelli, such as Franchi. In the Benelli implementation, a two part, rotating locking bolt, similar to that in many gas-operated
firearms, is used as basis of the action.
Before firing, the bolt body is separated from the locked bolt head by a stiff spring. As the shotgun recoils after firing, inertia causes the bolt body to remain stationary while the recoiling gun and locked bolt head move rearward. This movement compresses the spring between the bolt head and bolt body, storing the energy required to cycle the action. Since the spring can only be compressed a certain amount, this limits the amount of force the spring can absorb, and provides an inherent level of self-regulation to the action, allowing a wide range of shotshells to be used, from standard to magnum loads, as long as they provide the minimum recoil level to compress the spring. Note that the shotgun must be free to recoil for this to work--the compressibility of the shooter's body is sufficient to allow this movement, but firing the shotgun from a secure position in a rest or with the stock against the ground will not allow it to recoil sufficiently to operate the mechanism. Likewise, weapons of this type must be modified (with the addition of extended magazines or stock saddled ammunition slings on shotguns, for example) with care, as any sizable increase in weapon mass can reduce the force of recoil below that required to cycle the action.
As the recoil spring returns to its uncompressed state, it pushes the bolt body backward with sufficient force to cycle the action. The bolt body unlocks and retracts the bolt head, extracts and ejects the cartridge, cocks the hammer, and compresses the return spring. Once the bolt reaches the end of its travel, the return spring provides the force to chamber the next round from the magazine, and lock the bolt closed.
, use a mechanism at the muzzle to extract some energy from the escaping powder gases to push the barrel backwards, in addition to the recoil energy. This boost provides higher rates of fire and/or more reliable operation. This type of mechanism is also found in some suppressor
s used on short recoil firearms, under the name gas assist or Nielsen device, where it is used to compensate for the extra mass the suppressor adds to the recoiling parts both by providing a boost and decoupling some of the suppressor's mass from the firearm's recoiling parts.
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...
s. As the name implies, these actions use the force of recoil
Recoil
Recoil is the backward momentum of a gun when it is discharged. In technical terms, the recoil caused by the gun exactly balances the forward momentum of the projectile and exhaust gasses, according to Newton's third law...
to provide energy to cycle the action. Other operating systems are Blow forward operated
Blow forward
Blow-forward is a firearm operation where the barrel is virtually the only moving part of the weapon that is forced forward against a spring by the cartridge pressure and friction of the projectile against the rifling...
, blowback operated
Blowback (arms)
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 gases created by the ignition of the propellant charge....
, gas operated, gatling
Gatling gun
The Gatling gun is one of the best known early rapid-fire weapons and a forerunner of the modern machine gun. It is well known for its use by the Union forces during the American Civil War in the 1860s, which was the first time it was employed in combat...
, and chain
Chain gun
A chain gun is a type of machine gun or autocannon that uses an external source of power, rather than diverting energy from the cartridge, to cycle the weapon, and does so via a continuous loop of chain similar to that used on a motorcycle or bicycle. "Chain gun" is a registered trademark of...
.
Design
When the ejecta of a firearm (the projectile(s), propellant gas, wad, sabotSabot
A sabot is a device used in a firearm or cannon to fire a projectile, such as a bullet, that is smaller than the bore diameter, or which must be held in a precise position. The term is also applied to a battery stub case, a device used similarly to make a small electrical battery usable in a...
, etc.) are accelerated down the barrel of a firearm, all or a portion of the firearm will begin to move in the opposite direction, as required for conservation of momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
, according to the formula:
- Ejecta momentum = Recoiling momentum
which is calculated by:
- Ejecta mass × ejecta velocity = recoiling mass × recoil velocity
In non-recoil-operated firearms, it is generally the entire firearm that recoils. However, in recoil-operated firearms, only a portion of the firearm recoils while inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
holds another portion motionless relative to a mass such as the ground, a ship's gun mount, or a human holding the firearm. The moving and the motionless masses are coupled by a spring that absorbs the recoil energy as it is compressed by the movement and then expands providing energy for the rest of the operating cycle.
Since there is a minimum momentum required to operate a recoil-operated firearm's action, the 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...
must generate sufficient recoil to provide that momentum. Therefore, recoil-operated firearms work best with a cartridge that yields a momentum approximately equal to that for which the mechanism was optimized. For example, 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....
design with factory springs is optimized for a 230 gr bullet at factory velocity. Changes in caliber or drastic changes in bullet weight and/or velocity require modifications to spring weight or slide mass to compensate.
Long recoil operation
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, particularly ones based on John Browning
John Browning
John Moses Browning , born in Ogden, Utah, was an American firearms designer who developed many varieties of military and civilian firearms, cartridges, and gun mechanisms, many of which are still in use around the world...
's Auto-5
Browning Auto-5
The Browning Automatic 5, most often Auto-5 or simply A-5, is a recoil-operated semi-automatic shotgun designed by John Browning. It was the first successful semi-automatic shotgun designed and remained in production until 1998...
action. In a long recoil action, the barrel and bolt remain locked together during recoil, compressing the recoil spring or springs. Following this rearward movement, the bolt locks to the rear and the barrel is forced forward by the spring. The bolt is held in position until the barrel returns completely forward during which time the spent cartridge has been extracted and ejected, and a new shell has been positioned from the magazine. The bolt is released and forced closed by its recoil spring, chambering a fresh round.
The long recoil system is over a century old and dominated the automatic shotgun market for more than half that century before it was supplanted by new gas-operated
Gas-operated reloading
Gas-operation is a system of operation used to provide energy to operate autoloading firearms. In gas-operation, a portion of high pressure gas from the cartridge being fired is used to power a mechanism to extract the spent case and chamber a new cartridge. Energy from the gas is harnessed...
designs. While Browning halted production of the Auto-5 design in 1999, Franchi
Franchi
Luigi Franchi S.p.A. is an Italian manufacturer of firearms, most notably various shotguns.Notable Franchi products include the military SPAS-12 and SPAS-15 and the sporting-type long-recoil action AL-48. Franchi are renowned for their semi-automatic shotguns and are a division of Benelli...
still makes a long-recoil–operated shotgun line, the AL-48
Franchi AL-48
The 48 AL is a semi-automatic shotgun manufactured by Luigi Franchi S.p.A..The gun is available in a variety of calibers, including 12 gauge, 20 gauge and 28 gauge...
, which shares both the original Browning action design, and the "humpbacked" appearance of the original Auto-5. Other weapons based on the Browning system were the Remington Model 8
Remington Model 8
The Remington Model 8 is a centerfire, recoil-operated, semi-automatic rifle designed by John Browning and produced by Remington Arms beginning in 1906.John Browning was granted on October 16, 1900 for the rifle, which he then sold to Remington...
semi-automatic rifle (1906), the Remington Model 11 & "The Sportsman" model (a model 11 with only a 2 shell magazine) shotguns, the Frommer Stop
Frommer Stop
The Frommer Stop is a Hungarian long-recoil pistol manufactured by Fémáru-, Fegyver és Gépgyár [Metalware, Weapons and Machine Factory] in Budapest. It was designed by Rudolf Frommer, and its original design was adopted as the Pisztoly 12M in 1912, created for the Honvédség. The handgun was...
line of pistols (1907) and the Chauchat
Chauchat
The Chauchat , was the standard light machine gun of the French Army during World War I. Under the leadership of General Joseph Joffre, it was commissioned into the French Army in 1916. It was also widely used by the US Army in 1917-1918 and by six other nations: Belgium, Greece, Poland, Russia,...
machine rifle (1915).
Cycle diagram explanation
- Ready to fire position. Bolt is locked to barrel, both are fully forward.
- Recoil of firing forces bolt and barrel fully to the rear, compressing the return springs for both.
- Bolt is held to rear, while barrel unlocks and returns to battery under spring force. Fired round is ejected.
- Bolt returns under spring force, loads new round. Barrel locks in place as it returns to battery.
Short recoil operation
Automatic pistol
Automatic pistol may refer to:* Machine pistol, a handgun-style, magazine-fed and self-loading firearm, capable of fully automatic or burst fire, and chambered for pistol cartridges...
s, being found in nearly all such weapons chambered for 9x19mm Parabellum or higher-powered cartridges (weaker cartridges, .380 ACP
.380 ACP
The .380 ACP pistol cartridge is a rimless, straight-walled pistol cartridge developed by firearms designer John Browning. The cartridge headspaces on the mouth of the case. It was introduced in 1908 by Colt, and has been a popular self-defense cartridge ever since...
and below, generally use the blow-back
Blowback (arms)
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 gases created by the ignition of the propellant charge....
method of operation). Short recoil operation differs from long recoil operation in that the barrel and slide recoil together only a short distance before they unlock and separate. The barrel stops quickly, and the slide continues rearward, compressing the recoil spring and performing the automated extraction and feeding process. During the last portion of its forward travel, the slide locks into the barrel and pushes the barrel back into battery.
The exact method of locking and unlocking the barrel is the primary differentiating factor in the wide array of short recoil designs. Most common are the John Browning tilting barrel designs, based either on the swinging link and locking lugs as used in the M1911 pistol, or the linkless cam design used in the Hi Power
Browning Hi-Power
The Browning Hi-Power is a single-action, 9 mm semi-automatic handgun. It is based on a design by American firearms inventor John Browning, and completed by Dieudonné Saive at Fabrique Nationale of Herstal, Belgium. Browning died in 1926, several years before the design was finalized...
. Other common designs are the locking block design found in the 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...
, rollers in the MG42
MG42
The MG 42 is a 7.9mm universal machine gun that was developed in Nazi Germany and entered service with the Wehrmacht in 1942...
, or a rotating barrel used in the Steyr TMP
Steyr TMP
The Steyr TMP is a select-fire 9x19mm Parabellum caliber machine pistol manufactured by Steyr Mannlicher of Austria. The Magazines come in 15, 20, or 30 round detachable box types. A suppressor can also be fitted...
among others. One unusual variant is the 1890 toggle bolt
Toggle bolt
A toggle bolt is a fastener for hanging things on hollow walls such as drywall.Toggle bolts have wings that open inside a hollow wall, bracing against it to hold the fastener securely....
design of Hugo Borchardt
Hugo Borchardt
Hugo Borchardt was a firearms inventor and engineer, born in Magdeburg, Germany. He is known for his inventions of the Borchardt C-93 pistol and the Sharps-Borchardt Model 1878 rifle....
, used in the German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
Luger pistol
Luger pistol
The Pistole Parabellum 1908 or Parabellum-Pistole , popularly known as the Luger, is a toggle-locked recoil-operated semi-automatic pistol. The design was patented by Georg J...
.
While the short recoil design is most common in pistols, the very first short-recoil–operated firearm was also the first machine gun
Machine gun
A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute....
, the Maxim gun
Maxim gun
The Maxim gun was the first self-powered machine gun, invented by the American-born British inventor Sir Hiram Maxim in 1884. It has been called "the weapon most associated with [British] imperial conquest".-Functionality:...
. It used a toggle bolt similar to the one Borchardt later adapted to pistols. Vladimirov also used the short recoil principle in the Soviet KPV-14.5
KPV heavy machine gun
The KPV-14.5 heavy machine gun is a Soviet designed 14.5x114mm-caliber heavy machine gun, which first entered service as an infantry weapon in 1949. In the 1960s the infantry version was taken out of production because it was too big and heavy...
heavy machine gun which has been in service with the russian military and middle eastern armed forces for 80 years. Melvin Johnson also used the short recoil principle in his M1941 rifle & M1944 light machine gun.
Cycle diagram explanation
- Ready to fire position. Bolt is locked to barrel, both are fully forward.
- Upon firing, bolt and barrel recoil backwards a short distance while locked together. Near the end of the barrel travel, the bolt and barrel unlock.
- The barrel stops, but the unlocked bolt continues to move to the rear, ejecting the empty shell and compressing the recoil spring.
- The bolt returns forward under spring force, loading a new round into the barrel.
- Bolt locks into barrel, and forces barrel to return to battery.
Inertia operation
The newest design in recoil-operated firearms is the inertia operated system. In a reversal of the other designs, the inertia system uses nearly the entire firearm as the recoiling component, with only the bolt remaining stationary during firing. Because of this, the inertia system is only applied to heavily recoiling firearms, particularly shotguns. Currently the only inertia operated firearms are either made by BenelliBenelli (firearms)
Benelli Armi SpA is an Italian firearm manufacturer founded in 1967, located in Urbino, Italy, best known for high quality shotguns used by military, law enforcement and civilians all over the world. Particularly famous is the Benelli M3 12 gauge, used extensively by American SWAT teams...
, or use a design licensed from Benelli, such as Franchi. In the Benelli implementation, a two part, rotating locking bolt, similar to that in many gas-operated
Gas-operated reloading
Gas-operation is a system of operation used to provide energy to operate autoloading firearms. In gas-operation, a portion of high pressure gas from the cartridge being fired is used to power a mechanism to extract the spent case and chamber a new cartridge. Energy from the gas is harnessed...
firearms, is used as basis of the action.
Before firing, the bolt body is separated from the locked bolt head by a stiff spring. As the shotgun recoils after firing, inertia causes the bolt body to remain stationary while the recoiling gun and locked bolt head move rearward. This movement compresses the spring between the bolt head and bolt body, storing the energy required to cycle the action. Since the spring can only be compressed a certain amount, this limits the amount of force the spring can absorb, and provides an inherent level of self-regulation to the action, allowing a wide range of shotshells to be used, from standard to magnum loads, as long as they provide the minimum recoil level to compress the spring. Note that the shotgun must be free to recoil for this to work--the compressibility of the shooter's body is sufficient to allow this movement, but firing the shotgun from a secure position in a rest or with the stock against the ground will not allow it to recoil sufficiently to operate the mechanism. Likewise, weapons of this type must be modified (with the addition of extended magazines or stock saddled ammunition slings on shotguns, for example) with care, as any sizable increase in weapon mass can reduce the force of recoil below that required to cycle the action.
Cycle diagram explanation
- Ready to fire position. Bolt is locked to barrel, both are fully forward.
- Upon firing, the firearm recoils backwards into the shooter's body. The inertial mass remains stationary, compressing a spring. The bolt remains locked to the barrel, which in turn is rigidly attached to the frame.
- The compressed spring forces the inertial mass rearwards until it transfers its momentum to the bolt.
- The bolt unlocks and moves to the rear, ejecting the fired round and compressing the return spring.
- The bolt returns to battery under spring force, loading a new round and locking into place.
- The shooter recovers from the shot, moving the firearm forward into position for the next shot.
Muzzle booster
Some short-recoil–operated firearms, such as the German MG42MG42
The MG 42 is a 7.9mm universal machine gun that was developed in Nazi Germany and entered service with the Wehrmacht in 1942...
, use a mechanism at the muzzle to extract some energy from the escaping powder gases to push the barrel backwards, in addition to the recoil energy. This boost provides higher rates of fire and/or more reliable operation. This type of mechanism is also found in some suppressor
Suppressor
A suppressor, sound suppressor, sound moderator, or silencer, is a device attached to or part of the barrel of a firearm which reduces the amount of noise and flash generated by firing the weapon....
s used on short recoil firearms, under the name gas assist or Nielsen device, where it is used to compensate for the extra mass the suppressor adds to the recoiling parts both by providing a boost and decoupling some of the suppressor's mass from the firearm's recoiling parts.
Other autoloading systems
Other autoloading systems are:- Blow forwardBlow forwardBlow-forward is a firearm operation where the barrel is virtually the only moving part of the weapon that is forced forward against a spring by the cartridge pressure and friction of the projectile against the rifling...
firearms lack the use of a bolt but instead a moving barrel that gets dragged forward by the bullet until it leaves the barrel to cycle its action. - BlowbackBlowback (arms)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 gases created by the ignition of the propellant charge....
firearms use the expanding gas impinging on the cartridge itself to push the bolt of the firearm rearward. - ChainChain gunA chain gun is a type of machine gun or autocannon that uses an external source of power, rather than diverting energy from the cartridge, to cycle the weapon, and does so via a continuous loop of chain similar to that used on a motorcycle or bicycle. "Chain gun" is a registered trademark of...
and others utilize external power through electrical or hydraulic energy for operation. - Gas-operated reloadingGas-operated reloadingGas-operation is a system of operation used to provide energy to operate autoloading firearms. In gas-operation, a portion of high pressure gas from the cartridge being fired is used to power a mechanism to extract the spent case and chamber a new cartridge. Energy from the gas is harnessed...
- GatlingGatling gunThe Gatling gun is one of the best known early rapid-fire weapons and a forerunner of the modern machine gun. It is well known for its use by the Union forces during the American Civil War in the 1860s, which was the first time it was employed in combat...
and other mechanical means utilize mechanical energy from an operator turning a crank.
External links
- Recoil operation, Animations and explanations of (short) recoil operation principle at howstuffworks.com
- M2 Machine Gun Operation