The Probert Encyclopaedia of Warfare

CHAIN GUN

The chain gun was created to address the problem of traditional auto-cannons that if a round misfires or is defective, there isn't sufficient recoil to clear the shell and reload the gun and the gun jams. Chain guns use a separate motor to pull the ammunition belt through the gun breech. If a shell doesn't fire, the motor pulls the round out and loads a new one as though it had fired, preventing the jam which would occur otherwise. Jamming can still occur with chain guns, but is less frequent than with recoil loading automatic weapons, however the rate of fire is lower.
Research Chain Gun