The Supreme Court ruled Friday that a bump stock cannot be regulated as a machine gun device.

Bump stocks were banned by President Trump’s administration in 2019 after the deadliest mass shooting in American history, which saw a gunman kill 58 people and wound 500 others using weapons with bump stocks.

The court’s six-justice conservative majority ruled that, though a bump stock might enable a shooter to fire a semi-automatic weapon at a higher rate than would otherwise be possible, it does not allow a shooter to fire multiple rounds with only one activation of the trigger and thus cannot be regulated as a machine gun.

The conservative majority ruling against the regulation of firearms in America is another example of the high court tossing regulations on firearms.

In 2022 the Supreme Court forced multiple states across the country to completely rewrite their gun regulations in another landmark case, New York State Rifle and Pistol Association v. Bruen, which also saw the court divided along partisan lines. 

The court this summer is also expected to deliver an opinion on United States v. Rahimi, a case concerning whether states may restrict those facing domestic-violence restraining orders from owning guns.

The case decided Friday, Garland v. Cargill, revolved around the question of whether, for the purposes of regulation, a bump stock could be considered a machine gun because it is designed to convert a rifle into a “machine gun.”

In American law, a “machine gun” is defined as a firearm that is designed to shoot or can be readily made to shoot automatically, meaning a single manipulation of the trigger fires multiple shots.

In a detail key to this case, the regulator definition of “machine gun” applies to any part created to convert a weapon into a machine gun.

A “bump stock” is a device used in the technique shooters know as “bump firing” — using the recoil from a semi-automatic rifle to rapidly manipulate the trigger in order to achieve a high rate of fire, which approaches that of a machine gun.

Until 2017, a bump stock was not considered a machine gun for regulatory purposes. However, the Bureau of Alcohol, Tobacco, and Firearms changed this distinction in the wake of the mass shooting at Las Vegas.

While Congress moved, unsuccessfully, to regulate bump stocks, the ATF successfully proposed a change that ruled that bump stocks were machine guns.

One man who surrendered his bump stocks following the 2018 rule change, Michel Cargill, sued claiming that the ATF lacked the authority to make such a rule.

At court, the ATF argued that bump stocks should be regulated as machine guns because “they eliminate the manual movements that a shooter would otherwise need to make in order to fire continuously.”

In an opinion Friday, the court’s six conservative members ruled that, despite bump stocks allowing shooters to fire at a rate approaching that of a machine gun, the ATF overstepped its authority by regulating bump stocks as machine guns.

“Congress could have linked the definition of ‘machine gun’ to a weapon’s rate of fire,” Justice Clarence Thomas wrote for the majority. “But, it instead enacted a statute that turns on whether a weapon can fire more than one shot ‘automatically … by a single function of the trigger.’”

In a dissent, Justice Sonia Sotomayor, joined by the two other liberal justices, argued that the fact that a bump stock allows a shooter to shoot a semi-automatic rifle at rates similar to that of a machine gun without moving their trigger finger makes the stock tantamount to a machine gun for regulatory purposes.

Justice Sotomayor wrote that the majority, in its ruling, “casts aside Congress’s definition of ‘machine gun’ and seizes upon one that is inconsistent with the ordinary meaning of the statutory text and unsupported by context or purpose.”

“When I see a bird that walks like a duck, swims like a duck, and quacks like a duck, I call that bird a duck,” Justice Sotomayor wrote. “A bump-stock-equipped semiautomatic rifle fires ‘automatically more than one shot, without manual reloading, by a single function of the trigger.’”