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A chain gun is a type of autocannon or machine gun that uses an external source of power to cycle the weapon's action via a continuous loop of chain, similar to that used on a motorcycle or bicycle, instead of diverting excess energy from the cartridges' propellant as in a typical automatic firearm. [1] [2]
In 1972, Hughes Helicopters began a company-funded research effort to design a single machine gun to fire the U.S. Army's M50 20 mm round. [1] [2] In April 1973, the program fired test rounds in more powerful 30 mm WECOM linked ammunition, from a prototype A model. In January 1975, a model "C" was added, a linkless version for the proposed Advanced Attack Helicopter YAH-64. The helicopter was later adopted as the Hughes Model 77/AH-64A Apache, with the model C receiving the designation M230 chain gun as its standard armament. [1] [2]
In 1976, Hughes Helicopters patented the chain gun, [3] and it has since been further developed into several other systems of different calibers. [1] [2]
As of 2019 [update] , "chain gun" is a registered trademark of Northrop Grumman Innovation Systems, formerly Orbital ATK, following several mergers and acquisitions after Hughes Helicopters, for "externally-powered machine guns". [3]
There are several differences between chain guns and other types of autocannon. While rotary guns can also use an external source of power to cycle the weapon's mechanism, they have multiple rotating barrels, unlike chain guns. The necessary actions are performed by complex rotating cam mechanisms, not a chain.
Recoil-operated guns, e.g. many machine guns, the Bofors gun, and gas-operated guns, e.g. most assault rifles, the ShVAK cannon, depend upon the firing of the cartridges of the weapon's ammunition to power the cycle of action, instead of an external power source. As a cartridge may misfire - completely fail to fire, hang fire - or discharge with insufficient force to cycle the mechanism, this fundamental dependence affects the reliability of such weapons.
In contrast, in a chain gun the action of the firearm is cycled by a roller chain, driven by an electric motor. The chain moves in a rectangular circuit around four sprockets that apply tension to it. One link of the chain is connected to the bolt assembly, moving it back and forth to load, fire, extract, and eject cartridges.
Each full cycle consists of four different periods of the key link travelling along the circuit. Two periods, the passage along the "long" sides of the rectangle, control the movement of the bolt: the time that the bolt takes to drive forward and load a round into the chamber, and how quickly the bolt retracts and extracts the spent cartridge after firing. The other two periods, when the chain moves across the "short" sides of the rectangle, sideways relative to the axis of the barrel, determine how long the breech remains locked while firing, and open to allow cartridge extraction and ventilation of fumes.
A misfired round does not stop the functioning of the weapon, as it might with guns that use energy from a fired cartridge to load the next round. It is simply ejected. Thus, the chain gun operating principle is inherently reliable. An unclassified report on the EX-34 prepared by the Naval Surface Weapons Center in Dahlgren, Virginia, dated September 23, 1983, said that:
29,721 rounds of endurance tests were fired with no parts breakage and without any gun stoppages ... It is significant that during firing of 101,343 rounds not one jam or stoppage occurred due to loss of round control in the gun or feeder mechanism ... [this] is in our experience very unusual in any weapon of any caliber or type.
The time that the chain takes to move around a complete loop of the rectangle controls the rate of fire. Accordingly, varying the motor-speed allows a chain gun, in principle, to fire at a continuously variable rate from single rounds to the maximum safe rate. The maximum rate depends on the pressure drop rates in the barrel after firing a cartridge, on mechanical tolerances, and other factors. For example, the 7.62mm NATO version EX-34 was advertised to fire 570 rounds per minute, and developmental work was underway for a 1,000-rounds-per-minute version. In practice, chain guns usually have two or three set firing speeds.
| Chain Gun | Calibre | Uses |
|---|---|---|
| L94A1 | 7.62×51mm | AFVs such as Challenger 2 and FV510 Warrior (coaxial gun) |
| Profense PF 50 | 12.7×99mm | |
| Northrop Grumman Sky Viper | 20×102mm | Experimental derivative of the M230 |
| M242 Bushmaster | 25×137mm | AFVs such as the M2 Bradley and LAV-25, Mk 38 mount on warships |
| Mk44 Bushmaster II | 30×173mm | AFVs such as CV90, as the DS30M and Mk 46 mounts on warships |
| M230 | 30×113mmB | AH-64 Apache |
| Bushmaster III | 35×228mm | AFVs such as CV90 |
| Bushmaster IV | 40×365mmR | Uses the same ammunition as the Bofors 40mm L/70 cannon. |
| XM813 Bushmaster II | 40×180mm | |
| XM913 Bushmaster III | 50x228mm | Designed to fire the programmable XM1204 High Explosive Air Burst round [4] |
A machine gun (MG) is a fully automatic, rifled auto-loading firearm designed for sustained direct fire with rifle cartridges. Other automatic firearms such as automatic shotguns and automatic rifles are typically designed more for firing short bursts rather than continuous firepower and are not considered true machine guns. Submachine guns fire handgun cartridges rather than rifle cartridges, therefore they are not considered machine guns, while automatic firearms of 20 mm (0.79 in) caliber or more are classified as autocannons rather than machine guns.
The M2 machine gun or Browning .50 caliber machine gun is a heavy machine gun that was designed near the end of World War I by John Browning. While similar to Browning's M1919 Browning machine gun, which was chambered for the .30-06 cartridge, the M2 uses Browning's larger and more powerful .50 BMG cartridge. The design has had many designations; the official U.S. military designation for the infantry type is Browning Machine Gun, Cal. .50, M2, HB, Flexible. It has been used against infantry, light armored vehicles, watercraft, light fortifications, and low-flying aircraft.
The MK 108 is a 30 mm caliber autocannon manufactured in Germany during World War II by Rheinmetall‑Borsig for use in aircraft.
The M230 Cannon is a 30 mm (30×113 mm), single-barrel electrically-driven autocannon, using external electrical power to cycle the weapon between shots. It was designed and manufactured originally by Hughes Helicopters in Culver City, California. As of 2019, it is produced by Northrop Grumman Innovation Systems.
A revolver cannon is a type of autocannon, commonly used as an aircraft gun. It uses a cylinder with multiple chambers, similar to those of a revolver handgun, to speed up the loading-firing-ejection cycle. Some examples are also power-driven, to further speed the loading process. Unlike a rotary cannon, a revolver cannon only has a single barrel, so its spun weight is lower. Automatic revolver cannons have been produced by many different manufacturers.
The M134 Minigun is an American 7.62×51mm NATO six-barrel rotary machine gun with a high rate of fire. It features a Gatling-style rotating barrel assembly with an external power source, normally an electric motor. The "Mini" in the name is in comparison to larger-caliber designs that use a rotary barrel design, such as General Electric's earlier 20 mm M61 Vulcan, and "gun" for the use of rifle ammunition as opposed to autocannon shells.
The HS.404 is an autocannon originally designed by and produced by the Swiss arm of the Spanish/Swiss company Hispano-Suiza in the mid-1930s. Production was later moved to the French arm of Hispano-Suiza.
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.
Rate of fire is the frequency at which a specific weapon can fire or launch its projectiles. This can be influenced by several factors, including operator training level, mechanical limitations, ammunition availability, and weapon condition. In modern weaponry, it is usually measured in rounds per minute or rounds per second.
The M242 Bushmaster chain gun is a 25 mm (25×137mm) single-barrel chain-driven autocannon. It is used extensively by the U.S. military, such as in the Bradley fighting vehicle, as well as by other NATO members and some other nations in ground combat vehicles and various watercraft. Hughes Helicopters in Culver City, California, was the original designer and manufacturer. As of 2019, Northrop Grumman Innovation Systems produces the gun.
A rotary cannon, rotary autocannon, rotary gun or Gatling cannon, is any large-caliber multiple-barreled automatic firearm that uses a Gatling-type rotating barrel assembly to deliver a sustained saturational direct fire at much greater rates of fire than single-barreled autocannons of the same caliber. The loading, firing and ejection functions are performed simultaneously in different barrels as the whole assembly rotates, and the rotation also permits the barrels some time to cool. Rotary cannons, external or self-driven are used in aircraft over reciprocating bolt autocannons which are more prone to jamming in high g environments. The rotating barrels on nearly all modern Gatling-type guns are powered by an external force such as an electric motor, although internally powered gas-operated versions have also been developed.
The Oerlikon 20 mm cannon is a series of autocannons based on an original German Becker Type M2 20 mm cannon design that appeared very early in World War I. It was widely produced by Oerlikon Contraves and others, with various models employed by both Allied and Axis forces during World War II. Many versions of the cannon are still used today.
The ShKAS is a 7.62 mm calibre machine gun widely used by Soviet aircraft in the 1930s and during World War II. The ShKAS had the highest rate of fire of any aircraft machine gun in general service during WWII. It was designed by Boris Shpitalniy and Irinarkh Komaritsky and entered production in 1934. ShKAS was used in the majority of Soviet fighters and bombers and served as the basis for the ShVAK cannon.
The 37 mm Automatic Gun, M4, known as the T9 during development, was a 37 mm (1.46 in) recoil-operated autocannon designed by Browning Arms Company and entered service in 1942. The M4 and its variants would primarily be manufactured by Colt's Manufacturing Company and Oldsmobile and is therefore sometimes referred to as the "Colt M4" or "Oldsmobile M4." It was primarily mounted in the Bell P-39 Airacobra and P-63 Kingcobra, with the U.S. Navy also utilizing it on many PT boats.
The following are terms related to firearms and ammunition topics.
The Rikhter R-23 is an aircraft autocannon developed for the Soviet Air Force starting in the late 1950s. It was designed to be as short as possible to avoid problems found on high-speed aircraft when the guns were pointed into the airstream. The R-23 was a gas operated revolver cannon that used gas bled from holes in the barrel to provide the motive force. Firing up to 2,600 rpm, the R-23 was the fastest firing single-barrel cannon ever introduced into service.
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 propellant gas.
The Gryazev-Shipunov GSh-30-1 is a 30 mm autocannon designed for use on Soviet and later Russian military aircraft, entering service in the early 1980s. Its current manufacturer is the Russian company JSC Izhmash. The name GSH-30-1 is formed from the surnames of the designers Gryazev (Грязев) and Shipunov (Шипунов), the caliber of 30 mm and the single-barrel design of the gun itself.
The MK 115 was an autocannon developed in Germany in late World War II by Rheinmetall-Borsig for use in aircraft. It was an unusual development in that although it employed a locked breech, it also used a funnel to allow some of the propellant gases to escape out the rear in order to reduce recoil when firing, essentially being an automatic recoilless rifle. The MK 115 was chambered for a 5.5 cm round, but used a partially combustible cartridge, leaving only the base of the cartridge to eject. The MK 115 was a gas-operated, belt-fed weapon, and its breechblock used a swinging lock mechanism. It had a rifled barrel with an 8°30′ twist. A single prototype in the late stages of development was captured by the Western allies.
A repeating firearm or repeater is any firearm that is capable of being fired repeatedly before having to be manually reloaded with new ammunition into the firearm.