Abstract: An attachment or accessory, for semi-automatic firearm, comprising a housing releasably attached to the trigger guard of the firearm, a rotor member rotatably supported in the housing and having cams or lobes adapted to repeatedly actuate the firearm trigger through the intermediary of a rocker member actuated by the rotor cams when the rotor member is rotated. A lever-supported crank and a meshing pinion arrangement rotates the rotor through a one-way clutch coupling when the lever is displaced in one direction, the one-way clutch coupling disconnecting the rotor from the pinion when the lever is displaced in an opposite direction to a return position.