A bump stock and interface system for a semi-automatic firearm. In use, the user grasps a handle with one hand and places an index finger of the same hand firmly on a finger rest. When intending to fire a round of ammunition, the user pushes the firearm receiver forward with another hand so that the trigger collides with the immobilized finger on the finger rest. Recoil force separates the trigger from the user's finger on the finger rest. The user again pushes forward the receiver to repeat the firing cycle. A lock is selectively activated to arrest longitudinal movement of the firearm relative to the handle, thereby returning the firearm to normal semi-automatic functionality. The lock includes a retractable pin having a tip that rides in a track having a rear stop to limit over-travel of the handle.

A projectile launcher using a self-resetting trigger system includes a striker, a sear, and a trigger. The striker, also known as hammer, includes an anchoring notch and is able to slide between a firing position and a ready-for-firing position for launching an object. The sear, which is substantially L-shaped sear, has a first sear end and a second sear end wherein the sear maintains the striker to the ready-for-firing position when the first sear end engages with the anchoring notch of the striker. The trigger, which is capable of self resetting independent from the movement of the striker, contains an elastic lip with a ramp and is able to maintain the sear in a ready position when the elastic lip and the second sear end are coupled in a lock position.