The Supreme Court majority continued in relevant part: Even if a semiautomatic rifle with a bump stock could fire more than one shot “by a single function of the trigger,” it would not do so “automatically.” Section 5845(b) specifies the precise action that must “automatically” cause a weapon to fire “more than one shot”—a “single function of the trigger.” If something more than a “single function of the trigger” is required to fire multiple shots, the weapon does not satisfy the statutory definition. Firing multiple shots using a semiautomatic rifle with a bump stock requires more than a single function of the trigger. A shooter must maintain forward pressure on the rifle’s front grip with his non-trigger hand. Without this ongoing manual input, a semiautomatic rifle with a bump stock will not fire multiple shots.
ATF counters that machineguns also require continuous manual input from a shooter: The shooter must both engage the trigger and keep it pressed down to continue shooting. ATF argues there is no meaningful difference between holding down the trigger of a traditional machinegun and maintaining forward pressure on the front grip of a semiautomatic rifle with a bump stock. This argument ignores that Congress defined a machinegun by what happens “automatically” “by a single function of the trigger.” Simply pressing and holding the trig ger down on a fully automatic rifle is not manual input in addition to a trigger’s function. By contrast, pushing forward on the front grip of a semiautomatic rifle equipped with a bump stock is not part of functioning the trigger. Moreover, a semiautomatic rifle with a bump stock is indistinguishable from the Ithaca Model 37 shotgun, a weapon the ATF concedes cannot fire multiple shots “automatically.”
It would be helpful to the ATF if they could demonstrate that bump stocks have undergone significant developments since the agency took the position that semiautomatic weapons with bump stocks were not “machine guns.” Under those circumstances, the abandonment of ATF’s consistent position regarding bump stocks would make sense.
