The final rule adopts with minor changes the proposed amendments as stated in the NPRM. The final rule amends the regulatory text of “machine gun” by adding the following language: “The term ‘machinegun’ includes bump-stock-type devices, i.e., devices that allow a semiautomatic firearm to shoot more than one shot with a single pull of the trigger by harnessing the recoil energy of the semi-automatic firearm to which it is affixed so that the trigger resets and continues firing without additional physical manipulation of the trigger by the shooter.
Furthermore, the final rule defines “automatically” and “single function of the trigger” as those terms are used in the statutory definition of machinegun. Specifically, based on relevant case law, “automatically” means functioning as a result of a self-acting or self-regulating mechanism that allows the firing of multiple rounds through a single function of the trigger and “single function of the trigger” means single pull of the trigger and analogous motions. The NPRM proposed the same except for the term “single function of the trigger,” which was defined to mean “single pull of the trigger” without clarifying that “analogous motions” to a single trigger pull are included within that term, as stated in the final rule.