Hellfire trigger

A Hellfire trigger is a device that allows a semi-automatic firearm to fire at a rate approaching that of fully automatic firearms. When the trigger is pressed, the Hellfire device disengages the trigger return spring, which moves the operator's trigger finger. As a result, the operator can move his finger to fire individual shots more quickly. The Hellfire device may be used in conjunction with bump firing techniques to fire more rapidly.

The Hellfire 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.