Achain gunis a type ofautocannonormachine gunthat uses an external source of power to cycle the weapon'sactionvia acontinuous loop of chain,similar to that used on amotorcycleorbicycle,instead of diverting excess energy from thecartridges'propellantas in a typicalautomatic firearm.[1][2]
History
editIn 1972,Hughes Helicoptersbegan a company-funded research effort to design a single machine gun to fire theU.S. Army's M5020 mmround.[1][2]In April 1973, the program fired test rounds in more powerful30 mmWECOMlinked ammunition,from a prototype A model. In January 1975, a model "C" was added, a linkless version for the proposedAdvanced Attack HelicopterYAH-64. The helicopter was later adopted as theHughes Model 77/AH-64A Apache,with the model C receiving the designationM230 chain gunas 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 ofNorthrop Grumman Innovation Systems,formerly Orbital ATK, following several mergers and acquisitions after Hughes Helicopters, for "externally-powered machine guns".[3]
Design
editThere are several differences between chain guns and other types of autocannon. Whilerotary gunscan 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 rotatingcammechanisms, not a chain.
Recoil-operatedguns, e.g. manymachine guns,theBofors gun,andgas-operatedguns, e.g. mostassault rifles,theShVAK cannon,depend upon the firing of thecartridgesof 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 aroller chain,driven by anelectric motor.The chain moves in a rectangular circuit around foursprocketsthat apply tension to it. One link of the chain is connected to thebolt 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 theNaval Surface Weapons CenterinDahlgren, 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 therate 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, the7.62mm NATOversionEX-34was 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.
Examples
edit| Chain Gun | Calibre | Uses |
|---|---|---|
| L94A1 | 7.62×51mm | AFVssuch asChallenger 2andFV510 Warrior(coaxial gun) |
| Profense PF 50 | 12.7×99mm | |
| Northrop GrummanSky Viper | 20×102mm | Experimental derivative of the M230 |
| M242 Bushmaster | 25×137mm | AFVs such as theM2 BradleyandLAV-25,Mk 38 mount on warships |
| Mk44 Bushmaster II | 30×173mm | AFVs such asCV90,as theDS30Mand 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 theBofors 40mm L/70cannon. |
| XM813Bushmaster II | 40×180mm | |
| XM913Bushmaster III | 50x228mm | Designed to fire the programmableXM1204 High Explosive Air Burstround[4] |
See also
edit- AAI In-Line,prototype multiple-barrel externally driven machine gun using a chain.
- Polybolos
- Rotary cannon,often confused with a chain gun.
References
edit- ^abcdRichardson & Peacock, 1992, pp. 38–40.
- ^abcdChinn, George M.,1987, pp. 453–454.
- ^ab"Trademark Assignment Abstract of Title".United States Patent and Trademark Office.12 November 2018.Retrieved28 April2019.
- ^Ed Lopez (2020-07-09)."Army engineers develop greater lethality, speed to support future combat vehicle".US Army.Picatiny Arsenal,New Jersey.Retrieved2020-10-22.
Bibliography
edit- Chinn, George M. (Lt.Col. USMC Retd), ed. (1987).The Machine Gun: History, Evolution, and Development of Manual, Automatic, and Airborne Repeating Weapons(PDF).Vol. V. Ann Arbor, Michigan: Edward Brothers Publishing Co.Retrieved19 March2019.
- Richardson, Doug & Peacock, Lindsay (1992).Combat Aircraft: AH-64 Apache.London: Salamander Books.ISBN0-86101-675-0.
- U.S. Army Field Manual 3-22.1