Page "Chain gun" Paragraph 2

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.