Blowback is a system in which automatic or semi-automatic firearms operate through the energy created by combustion in the chamber and bore acting directly on the bolt face through the cartridge. Other operating systems are recoil operation, gas-actuated, gatling and chain. M2 machine gun An automatic firearm is a firearm that will continue to load and fire ammunition as long as the trigger (or other activating device) is pressed or until it runs out of ammunition. ... Walther P99, a semiautomatic pistol from the late 1990s A semi-automatic firearm is a gun that requires only a trigger pull for each round that is fired, unlike a single-action revolver, a pump-action firearm, a bolt-action firearm, or a lever-action firearm, which require the shooter... An assortment of modern handheld firearms using fixed ammunition, including military assault rifles, a sporting shotgun (fourth from bottom), and a tactical shotgun (third from bottom). ... Recoil operation is a type of locked-breech firearm actions used in automatic firearms. ... The gas-operated system for implementing automatic reloading of a firearm is one of five such systems, the others being recoil-operated, gatling, chain, and blowback. ... An 1865 Gatling gun. ... The M242 25mm Chain gun A chain gun is a type of machine gun or autocannon that uses an external source of power, rather than recoil, to cycle the weapon. ...

In the blowback system there is no positive lock between the bolt and the barrel. The mass of the bolt and force of its recoil spring act to keep the breech closed. The expanding gases from the fired round overcome this inertia and "blow back" the breech. The breech must be kept closed until the round has left the barrel and gas pressures have subsided. The weight of the bolt is the major factor in determining this, and to remain practical this system is only really useful for weapons using relatively low pressure rounds. Pure blowback operation is typically found only on semi-automatic small-caliber pistols and automatic submachine guns. Even using comparitively weak ammunition, the lack of resistance makes for a very snappy and uncomfortable amount of felt recoil as compared to the delayed blowback action used in handguns like the .45 ACP 1911 or 9mm Glock, which, even though they typically fire much more powerful cartridges, are much more comfortable to fire. There are also some low-velocity cannon or grenade launchers using blowback, derived from the MK 108. One of these is the Mk 19 grenade launcher. A Browning 9 millimeter Hi-Power Ordnance pistol of the French Navy, 19th century, using a Percussion cap mechanism Derringers were small and easily hidden. ... An MP5A4 (fixed stock and 3-round burst trigger group), a popular modern submachine gun A submachine gun is a firearm that combines the automatic fire of a machine gun with the cartridge of a pistol, and is usually between the two in weight and size. ... A small cannon on a carriage, Bucharest. ... The MK 108 (German: Maschinenkanone - Machine Cannon) was an autocannon (30mm calibre) manufactured in Germany during World War II by Rheinmetall-Borsig for use in aircraft. ... MK-19 40mm grenade launcher during MIL-EX 2003 The MK19 (also known as MK-19, M19, Mark 19, or Mk 19) is a belt-fed grenade machine gun capable of firing five grenades per second. ...

For more powerful rounds and for lighter operating systems, some form of delayed or retarded blowback can be used, in which the bolt has to overcome some initial resistance while moving. There are various forms of delaying mechanism:

• roller-delayed blowback, as in the HK G3
• gas-delayed blowback, as in the HK P7
• lever-delayed blowback, as in the FAMAS
• Chamber-ring delayed blowback, as in the Seecamp pistol
• Hesitation locked as in the Remington 51 pistol

While the above are effective delay mechanisms, there were some delaying systems which did not work as advertised. Two notable mechanisms are the Blish lock and Savage rotating barrel pistols. The Blish Lock used the dubious principle of dissimilar metal adhesion to delay the opening of the breech. It was eventually eliminated from the Thompson submachinegun as redundant. The Savage system theorized that the rifling in the barrel caused a rotational force that would hold the gun locked until the projectile left the barrel. It was later discovered that the bullet had left the barrel long before any locking could occur and that Savage pistols merely operated on a pure blowback basis; the rotation of the barrel might play a minor role by slowing the rearward motion of the slide as the slide cycled. Roller-delayed blowback is a firearm operating principle, a refined form of blowback. ... The Heckler und Koch G3 The G3 (G3A3) series battle rifle is manufactured by Heckler und Koch. ... Gas-delayed blowback (also called gas-retarded blowback) is a firearm operating principle (not to be confused with gas-operated). ... The Heckler & Koch P7 is a compact semi-automatic pistol normally chambered in 9 x 19 mm Luger manufactured by the German company of Heckler & Koch. ... The FAMAS (Fusil dAssaut de la Manufacture dArmes de St-Etienne, Assault Rifle by St-Etienne Arms Factory) is an assault rifle in bullpup configuration designed and manufactured in France by the Saint Étienne arms factory, which is a member of the French government-owned GIAT Industries complex. ... Chamber-ring delayed blowback is a method for slowing the opening of Blowback (arms) operated automatic or semi-automatic firearms whereby a raised ring at the rear of the chamber restricts the rearward movement of the slide. ... L. W. Seecamp is a manufacturer of high quality, hand made pocket pistols located in Milford, Connecticut from 1981 to present. ... Model 51 Type Pocket Pistol Nationality America Era Early 20th Century History Date of design {{{date}}} Production period {{{prod_date}}} Service duration {{{serv_date}}} Operators George S. Patton War service WW II (Informal) Specifications Type Pistol Calibre 380 ACP / 32 ACP Barrel length {{{barrel}}} Ammunition Round-Nosed only Magazine Box Action Semi... Model 51 Type Pocket Pistol Nationality America Era Early 20th Century History Date of design {{{date}}} Production period {{{prod_date}}} Service duration {{{serv_date}}} Operators George S. Patton War service WW II (Informal) Specifications Type Pistol Calibre 380 ACP / 32 ACP Barrel length {{{barrel}}} Ammunition Round-Nosed only Magazine Box Action Semi... The Blish Lock is a friction-lock designed by John Bell Blish, that takes advantage of the fact that under extreme pressures, certain dissimilar materials will resist movement through friction greater than normal friction laws would predict. ... // Savage Arms was founded in 1894 by Arthur Savage in Utica, NY. Perhaps best-known for the Savage Model 99 which is a hammerless lever action rifle, which is no longer in production. ... The Thompson submachine gun, also known as the Tommy gun, was an American submachine gun (SMG) that became infamous during the Prohibition era. ...

• Blowback can also refer to the combination of gasses, dirt, and debris (unburnt powder, metal shavings) that most firearms produce upon firing. This can cause great irritation to the eyes and most ranges or organizations suggest or require the use of safety glasses when firing pistols.

External links

• Blowback action, Animation and explanation at howstuffworks.com