A machine gun top cover assembly includes a top cover door attached to a main housing. The top cover assembly defines a rear transverse track section and a front transverse track section for guiding bolt assemblies of the gun. As the machine gun rotor assembly rotates, the rear track section prevents the bolt assemblies from moving into position for firing, and the front track section guides the bolt assemblies into position for firing. A selector switch on the top cover door selects between: (i) a safe position wherein, each of the bolt assemblies are sequentially directed into the rear track section; and (ii) a fire position wherein the bolt assemblies are directed into the front track section. The top cover assembly can include a solenoid for moving the selector switch between the safe position and the fire position in response to an electrical control signal.