The Supreme Court's 6-3 ruling in Garland v. Cargill was based purely on the statutory text. The National Firearms Act defines "machinegun" as "any weapon which shoots … automatically more than one shot, without manual reloading, by a single function of the trigger…." A bump stock is a device that allows a semiautomatic rifle to fire more rapidly by pulling the trigger and maintaining forward pressure on the handguard, which harnesses recoil to continue firing.
The opinion by Justice Clarence Thomas includes extensive technical information on how the internal parts of AR-15 rifles function, including diagrams and an animated graphic showing the movement of the parts. Firing a rifle with a bump stock still requires a separate function of the trigger for each shot, and it is not "automatic" because it will not fire without constant manual pressure on the handguard. The Court has never before ventured into such a detailed explanation about how a firearm works.
While the Court's discussion of how the trigger, sear, disconnector, and bolt interact in the firing sequence is quite technical, the decision embodies broader implications that are significant in other contexts.
