Chain gun A chain gun is a type of machine gun or autocannon 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 . 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 to drive the chain that moves in a rectangular circuit via four sprocket 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 cartridge s . 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 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 . " Examples . A commonly used chain gun is the M242 Bushmaster . Versions of its 25 mm action are found on ships ( the Mk38 ) and Infantry fighting vehicle s ( the M2 Bradley and LAV - 25 ) around the world . Others are the M230 30 mm Cannon , which is standard equipment on the Apache helicopter , as well as the Bushmaster II 30 mm , and the Bushmaster III 35 / 50 mm Chain gun . 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 . Distinction from Gatling guns . A chain gun has a single barrel , while a Gatling gun / Minigun has several rotating barrels and internally do not use chains to drive the weapon . 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 " ) . The only multiple barrel firearm that could be described as a " chain gun " would be the Johnston machine gun as it uses a chain drive to rotate the barrels .