A system includes a movable assembly configured for pushing a piece of ammunition into a breech ring of a firearm and/or closing the breech ring, under control of a motor. A feeding device is configured for feeding the piece of ammunition into a position situated between the movable assembly and the breech ring. A synchronization device co-operates with the motor on one side and with the feeding device on the other side. The synchronization mechanism provides for selective transmission of motion, under control of the movable assembly, from the motor to the feeding mechanism, when the movable assembly is in a position away from the breech ring.