Editing Chain gun

{{Short description|Firearm mechanism that uses an external source of power to cycle the firearm}}
{{Lead too short|date=June 2021}}
{{Not to be confused with|Belt (firearms)}}
[[File:M242-2.png|thumb|The [[M242]] 25&nbsp;mm chain gun]]
A '''chain gun''' is a type of [[autocannon]] or [[machine gun]] that uses an external source of power to cycle the weapon's [[action (firearms)|action]] via a [[chain drive|continuous loop of chain]], similar to that used on a [[motorcycle]] or [[bicycle]], instead of diverting excess energy from the [[cartridge (firearms)|cartridge]]s' [[propellant]] as in a typical [[automatic firearm]].<ref name=R&P/><ref name=CGM/>

==History==
In 1972, [[Hughes Helicopters]] began a company-funded research effort to design a single machine gun to fire the [[United States Army|U.S. Army]]'s M50 {{nobr|20 mm}} round.<ref name=R&P/><ref name=CGM/> In April 1973, the program fired test rounds in more powerful {{nobr|30 mm}} WECOM [[Belt (firearms)|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 [[Boeing AH-64 Apache|Hughes Model 77/AH-64A Apache]], with the model C receiving the designation [[M230 chain gun]] as its standard armament.<ref name=R&P/><ref name=CGM/> 

In 1976, Hughes Helicopters patented the chain gun,<ref name="USPTO" /> and it has since been further developed into several other systems of different calibers.<ref name="R&P">Richardson & Peacock, 1992, pp. 38–40.</ref><ref name="CGM">[[George Chinn|Chinn, George M.]], 1987, pp. 453–454.</ref>

[[File:Chaingun.jpg|thumb|A M242 [[Mk38#Naval|Mk 38 chain gun]] mounted on [[USS Nicholas (FFG-47)]]]]

{{As of|2019}}, "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".<ref name="USPTO">{{cite web |url=http://assignments.uspto.gov/assignments/q?db=tm&qt=sno&reel=&frame=&sno=73027311 |title=Trademark Assignment Abstract of Title |publisher=[[United States Patent and Trademark Office]] |date=12 November 2018 |access-date=28 April 2019}}</ref>

==Design==
There are several differences between chain guns and other types of autocannon. While [[rotary gun]]s 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 (mechanism)|cam]] mechanisms, not a chain. 

[[Recoil operation|Recoil-operated]] guns, e.g. many [[machine gun]]s, the [[Bofors 40 mm L/60 gun|Bofors gun]], and [[gas-operated reloading|gas-operated]] guns, e.g. most [[assault rifle]]s, the [[ShVAK cannon]], depend upon the firing of the [[cartridge (firearms)|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 [[sprocket]]s that apply tension to it. One link of the chain is connected to the [[bolt (firearms)|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 Warfare Center Dahlgren Division|Naval Surface Weapons Center]] in [[Dahlgren, Virginia]], dated September 23, 1983, said that:<blockquote>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.</blockquote>

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 [[7.62×51mm NATO|7.62mm NATO]] version [[L94A1 chain gun|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.

==Examples==
{| class="wikitable"
|-
! Chain Gun
! Calibre
! Uses
|-
| [[L94A1 chain gun|L94A1]]
| [[7.62×51mm]]
| [[Armoured fighting vehicle|AFVs]] such as [[Challenger 2]] and [[Warrior tracked armoured vehicle|FV510 Warrior]] (coaxial gun)
|-
| [[AAI In-Line]]
| [[7.62×51mm]]
| Prototype [[Multiple-barrel firearm|multiple-barrel]] externally driven machine gun using a chain.
|-
| [[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 40 mm Automatic Gun L/70|Bofors 40mm L/70]] cannon.
|-
| [[XM813]] Bushmaster II
| 40×180mm
|
|-
| [[XM913 chain gun|XM913]] Bushmaster III
| 50x228mm
| Designed to fire the programmable [[XM1204 High Explosive Air Burst]] round<ref name=xm1204Mil2020-07-09/>
|}

==See also==
* [[Polybolos]]
* [[Rotary cannon]], often confused with a chain gun.

==References==
{{reflist|refs=
<ref name="xm1204Mil2020-07-09">{{ cite news | url = https://www.army.mil/article/237156/army_engineers_develop_greater_lethality_speed_to_support_future_combat_vehicle | title = Army engineers develop greater lethality, speed to support future combat vehicle | date = 2020-07-09 | author = Ed Lopez | work = [[US Army]] | location = [[Picatiny Arsenal]], [[New Jersey]] | access-date = 2020-10-22 }}</ref>
}}

==Bibliography==
* {{ cite book |editor-first=George M. (Lt.Col. USMC Retd) |editor-last=Chinn |title=The Machine Gun: History, Evolution, and Development of Manual, Automatic, and Airborne Repeating Weapons |volume=V |publisher=Edward Brothers Publishing Co. |location=Ann Arbor, Michigan |year=1987 |url=http://www.ibiblio.org/hyperwar/USN/ref/MG/V/MG-V5.pdf |access-date=19 March 2019 }}
* {{ cite book|last1=Richardson |first1=Doug |first2=Lindsay |last2=Peacock |title=Combat Aircraft: AH-64 Apache |location=London |publisher=Salamander Books |year=1992 |isbn=0-86101-675-0 |name-list-style=amp }}
* [https://www.globalsecurity.org/military/library/policy/army/fm/3-22-1/index.html U.S. Army Field Manual 3-22.1]

==External links==
* [http://www.northropgrumman.com/Capabilities/AutomaticWeapons/Pages/default.aspx Northrop Grumman - Bushmaster Chain Guns and Automatic Cannons]
* [https://web.archive.org/web/20040606114844/http://tri.army.mil/LC/CS/csa/aptoc.htm U. S. Army TACOM-RI]
* [https://patents.google.com/patent/US4481858A/en]
* [https://patents.google.com/patent/US10852085B2/en]

{{Chain guns}}

[[Category:Machine guns]]
[[Category:Chain guns]]
[[Category:Autocannon]]