Bump fire
Bump firing is the act of using the recoil of a semi-automatic firearm to fire multiple shots in rapid succession, which very crudely simulates the discharge of a fully automatic firearm. This process involves holding the foregrip 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 finger from the trigger, and keeping the trigger finger stationary. During a shot, the firearm will recoil considerably ("bump" back) and the trigger will reset itself; then the non-trigger hand would naturally force the firearm back to the original position, pressing the trigger against a stationary finger again, thereby firing successive shots.
This technique is usually used for entertainment, as the drawback of decreased accuracy eliminates any conceivable "tactical" advantage that might be gained.
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 weapon forwards while the trigger fingers remain stationary. With revolvers, automatic fire can be simulated by using two trigger fingers firing offset.
All these techniques greatly degrade the accuracy of the firearm, due to the necessary jerking of the weapon, which makes viable aiming impossible. The techniques trade accurate, aimed fire for an increase in the firearm's rate of fire. With bump-firing it is common to "empty the mag" with at least one stoppage. The inaccuracy, difficulty, and ammunition costs render the practice uncommon.
Devices (from complicated, specially made triggers to the low-tech rubber band) may be employed in order to aid in the "bumping". However, not all such devices or modifications are legal. A famous example in the United States of America is the case of the Akins Accelerator for the Ruger 10/22.[1] Though the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) initially approved the device, they later reversed this ruling, two years after they had approved it for sale. Some states, such as California, ban the manufacture, use, sale, and possession of such devices. Such devices are also prohibited in Canada, as Canadian laws ban "Any electrical or mechanical device that is designed or adapted to operate the trigger mechanism of a semi automatic firearm for the purpose of causing the firearm to discharge cartridges in rapid succession".