M61A1 Vulcan

The M61 operates on the Gatling principle – six 20-mm barrels are mounted on a geared rotor that is driven by a 20-hp electric motor. As the motor turns the rotor, the cam follower on the bolt of each rotating barrel follows a fixed cam path in the gun housing, opening and closing the bolt once per revolution. Firing only once per revo­lution reduces each barrel’s rate of fire to below that of most single-barrel revolver can­non. GE claims that this continuous rotary motion eliminates the impact loads on gun components and that sharing the thermal duty cycle among six barrels ‘significantly’ increas­es barrel life. The use of external power elimi­nates jamming due to a misfired round. […]