Semi-automatic firearms shoot once per trigger action.
Machineguns shoot continuously while the trigger is pulled.
Bump stocks are a combination of stock and grip. They have no mechanism for holding the trigger down, and they do not alter the way the gun shoots.
News reports on the Supreme Court’s first day of oral arguments in the case of Garland v. Cargill with their line of questioning suggesting the court may be inclined to uphold the Trump-era ban on bump stocks by the ATF, but not yet fully signaling whether a majority of justices would eventually back such a ruling. There was abundant debate with liberal justices drawing the usual line against anything supportive of gun rights and the conservative justices asking questions that reveal they are seriously weighing the value as well as drawbacks to overriding the ATF’s decision.
Here’s a list of questions and quotes shared from the oral arguments according to ABC News and other news reports:
Justice Samuel Alito: “Can you imagine a legislator thinking we should ban machine guns but we should not ban bump stocks?”