Chain gun

Chain gun

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A chain gun is a type of 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....

 or autocannon
Autocannon
An autocannon or automatic cannon is a rapid-fire projectile weapon firing a shell as opposed to the bullet fired by a machine gun. Autocannons often have a larger caliber than a machine gun . Usually, autocannons are smaller than a field gun or other artillery, and are mechanically loaded for a...

 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 Alliant Techsystems Inc.
Alliant Techsystems
Alliant Techsystems Inc., most commonly known by its ticker symbol, ', is one of the largest aerospace and defense companies in the United States with more than 18,000 employees in 22 states, Puerto Rico and internationally, and 2010 revenues in excess of an estimated...

 for a chain-powered weapon.

Description


Reliability and controllability are the advantages of chain-driven weapons over their recoil-actuated counterparts. Instead of depending upon the sometimes unreliable firing of a cartridge to power the cycle of action, a chain gun uses an electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

 to drive the chain that moves in a rectangular circuit via four sprocket
Sprocket
A sprocket or sprocket-wheel is a profiled wheel with teeth, cogs, or even sprockets that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which are radial projections that engage a chain passing over it...

s 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.

As with all guns that do not use energy from a fired cartridge to load the next round, a misfired round does not stop the functioning of the weapon; it is simply ejected.

During each full cycle of four periods, two periods (passage along the "long" sides of the rectangle) control the time the bolt takes to drive forward and load a round into the chamber, and how quickly it extracts it. 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.

Since the time the chain takes to move around a complete loop of the rectangle controls the rate of fire, varying the motor speed allows chain guns, in principle, to fire at a rate continuously variable from single rounds to the maximum safe rate imposed by the pressure drop rates in the barrel after firing a cartridge, mechanical tolerances, and other factors. For example, the 7.62mm NATO version EX-34 was advertised to offer 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.

The chain gun operating principle is inherently reliable. An unclassified report on the EX-34 prepared by the Naval Surface Weapons Center
Naval Surface Warfare Center Dahlgren Division
The United States Naval Surface Warfare Center, Dahlgren Division , named for Rear Admiral John A. Dahlgren, is located in Dahlgren, Virginia and is part of the Naval Surface Warfare Center. The NSWCDD was founded as the U.S...

 in Dahlgren, Virginia
Dahlgren, Virginia
Dahlgren is a census-designated place in King George County, Virginia, United States. The population was 997 at the 2000 census. The community is located within the Northern Neck George Washington Birthplace American Viticultural Area winemaking appellation established by the United States...

, 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.

Examples


A commonly used chain gun is the M242 Bushmaster
M242 Bushmaster
The M242 Bushmaster is a 25 mm chain-fed autocannon. It is used extensively by the US armed forces, as well as by NATO's and some other nations' forces in ground combat vehicles and watercraft...

. Versions of its 25 mm action are found on ships (the Mk38) and Infantry fighting vehicle
Infantry fighting vehicle
An infantry fighting vehicle , also known as a mechanized infantry combat vehicle , is a type of armoured fighting vehicle used to carry infantry into battle and provide fire support for them...

s (the M2 Bradley
M2 Bradley
The Bradley Fighting Vehicle is an American fighting vehicle platform manufactured by BAE Systems Land and Armaments, formerly United Defense.As with other infantry fighting vehicles, the Bradley is designed to transport infantry with armor protection while providing covering fire to suppress enemy...

 and LAV-25
LAV 25
The LAV-25 is an eight-wheeled amphibious reconnaissance vehicle used by the United States Marine Corps. It was built by General Dynamics Land Systems Canada and is based on the Swiss MOWAG Piranha I 8x8 family of armored fighting vehicles....

) around the world. Others are the M230 30 mm Cannon, which is standard equipment on the Apache
AH-64 Apache
The Boeing AH-64 Apache is a four-blade, twin-engine attack helicopter with a tailwheel-type landing gear arrangement, and a tandem cockpit for a two-man crew. The Apache was developed as Model 77 by Hughes Helicopters for the United States Army's Advanced Attack Helicopter program to replace the...

 helicopter
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...

, as well as the Bushmaster II 30 mm
Bushmaster II
The Mk44 Bushmaster II is a 30 mm chain gun manufactured by Alliant Techsystems. It is a derivative of the 25 mm M242 Bushmaster, and uses some 70% of the same parts as the M242 while increasing the firepower by as much as 50% with the 20% increase in caliber size. The barrel is chromium-plated...

, and the Bushmaster III 35/50 mm Chain gun
Bushmaster III
The Bushmaster III is an automatic/semi-automatic cannon designed and built by Alliant Techsystems. It is based on the M242 Bushmaster originally developed by Alliant Techsystems...

.

A 7.62x51mm NATO caliber chain gun is used on some armored vehicles as a coaxial machine gun, because of the inherently small amount of fumes from spent propellant discharged inside of the vehicle. A developmental version of this gun was named EX-34. It is in use as the L94A1 chain gun with the British Army
British Army
The British Army is the land warfare branch of Her Majesty's Armed Forces in the United Kingdom. It came into being with the unification of the Kingdom of England and Scotland into the Kingdom of Great Britain in 1707. The new British Army incorporated Regiments that had already existed in England...


Distinction from Gatling guns


A chain gun has a single barrel while a Gatling gun
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...

 has several rotating barrels. It is a common error to refer to Gatling guns as chain guns, particularly in connection with entertainment such as video games (notably the popular first-person shooter Doom
Doom (series)
Doom is a series of first-person shooter video games developed by id Software. The series focuses on the exploits of an unnamed space marine operating under the UAC , who fights hordes of undead and demons in order to survive...

).

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