How a Bump Stock works

The bump firing process involves bracing the rifle with the non-trigger hand, releasing the grip on the firing hand (leaving the trigger finger in its normal position in front of the trigger), pushing the rifle forward in order to apply pressure on the trigger from the finger, and keeping the trigger finger stationary. During a shot, the firearm will recoil ("bump" back) and the trigger will reset as it normally does; then, the non-trigger hand pulls the firearm away from the body and back to the original position, pressing the trigger against the stationary finger again, thereby firing another round when the trigger is pushed back.

Normally, a rifle is held securely and firmly against the shoulder, but the loose shoulder hold that creates the rattle to rapidly depress the trigger affects accuracy in a way that is not encountered with firearms that are designed for select-fire.

A similar method can be employed with semi-automatic pistols, in which one hand holds the grip, two fingers are placed in the trigger well, and then the grip hand shoves the firearm forward while the trigger fingers remain stationary. With revolvers, rapid fire can be achieved by using two trigger fingers firing offset.