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 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.
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 . . . is in our experience very unusual in any weapon of any caliber or type.
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