Devices, systems, and methods of manufacturing are disclosed with regard to a rapid-fire accessory that mounts onto a semi-automatic firearm using structural features thereof and/or added thereon to guide a trigger actuator for engaging a trigger and repeatedly firing the semi-automatic firearm. The rapid-fire accessory does not require the removal or replacement of the original, replacement, or aftermarket firearm grip or most other components of the firearm. The rapid-fire accessory provides a structural component an operator may hold that facilitates bump firing the semi-automatic firearm. Once mounted on the semi-automatic firearm, the rapid-fire accessory may slide rearward and forward, using a bottom rail on or below a forend of the semi-automatic firearm as a guiding surface and securing element. The rapid-fire accessory also includes a forward-hand grip for comfortably and securely holding the rapid-fire accessory steady, while the semi-automatic firearm is pushed forward and then recoils backward from discharging.