The US Court of Appeals for the Fifth Circuit Tuesday upheld the federal ban on bump stocks, a firearm accessory that allows semiautomatic guns to fire like automatic weapons.

The Trump administration outlawed bump stocks after a 2017 shooting in Las Vegas where the rapid-fire accessory was used to kill 58 people. The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) promulgated a rule stating that bump stocks were machine guns for purposes of the National Firearms Act (NFA) and the federal prohibition on the possession or sale of machine guns.

Plaintiff Michael Cargill challenged the rule. He argued that it contradicts the plain language of the NFA, that it exceeds ATF’s statutory authority and that it violates the separation of powers among the branches of government. However, the trial court concluded that ATF properly classified a bump stock as a machine gun, as defined by the statute.

On appeal, the Fifth Circuit affirmed the trial court’s decision. The court found that the rule’s interpretation of “single function of the trigger” as meaning a single pull of the trigger and analogous motions was compelling. When the rule was promulgated “function” and “pull” were both used almost interchangeably. The court refused to adopt a mechanistic interpretation of the statute.

The court further rejected Cargill’s argument that the court must resolve any ambiguity in the statute in his favor under the rule of lenity. The court found that there was no “grievous ambiguity or uncertainty” because the rule’s interpretation of “machinegun” was the best interpretation of the statute. Therefore, the court upheld the ban.

Other courts, including the US Supreme Court, have rejected challenges to the federal ban on bump stocks. In March 2019, the US Supreme Court denied an application for stay of the order from a Michigan District Court refusing to block the ban. In March 2020, the Supreme Court denied a petition by bump-stock owners and gun advocacy groups to hear a case challenging the ban. More recently, on December 3, the US Court of Appeals for the Sixth Circuit affirmed the ban in the case of Gun Owners of Am., Inc. v. Garland.