A bump stock is a modified stock that can be attached to a semiautomatic firearm to enable it to fire bullets more rapidly. Several months after the deadly 2017 Las Vegas mass shooting, in which the shooter attached bump stocks to several of his semi-automatic weapons, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) issued a federal rule banning the use of bump stocks.
The ATF's administrative decision made semi-automatic firearms with bump stocks equivalent to machine guns because they "allow a shooter of a semi-automatic firearm to initiate a continuous firing cycle with a single pull of the trigger." (Related: Federal appeals court overwhelmingly overturns Trump-era ban on rifle bump stocks.)
The ban went into effect in 2019 and made possession of bump stocks. a federal crime carrying a penalty of up to 10 years in prison and a $250,000 fine.
The Supreme Court refused to intervene to block the ATF from enforcing this ban. This led Michael Cargill, owner of Central Texas Gun Works in Austin, to challenge the law in federal court. He initially lost his challenge in federal district court before a three-judge panel of the Fifth Circuit. He appealed this decision and won in the Fifth Circuit's appeals court.