The final rule clarifies that the definition of “machinegun” in the Gun Control Act (GCA) and National Firearms Act (NFA) 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 semiautomatic firearm to which it is affixed so that the trigger resets and continues firing without additional physical manipulation of the trigger by the shooter.