Hell-Fire trigger is a device that allows a semi-automatic firearm to fire at a rate approaching that of a fully automatic firearm . The Hell-Fire clamps to the trigger guard behind the trigger and presses a " finger " against the back of the trigger to increase the force that returns the trigger to its forward position , effectively reducing the amount of finger movement required to actuate the trigger and allows for a significantly higher rate of fire . Technically , the firearm is not altered . As in all semi-automatic firearms , only one round is fired with every stroke of the trigger . The Hell-Fire trigger was used , with a pair of TEC-9 pistols , by the perpetrator of a 1993 mass shooting that killed nine people . Separately , David Koresh , leader of the Branch Davidians , reportedly told authorities that he utilized semi-automatic guns with the part installed
1993 mass shooting
101 California Street shooting
Hell-Fire trigger