The Supreme Court has ruled that bump stocks don’t qualify as machine guns under federal gun controls, shooting down the Justice Department’s attempt to ban the devices.

In the 6-3 ruling on Friday, split along the court’s ideological lines, Justice Clarence Thomas said there are important differences between an actual machine gun and bump stocks, which are attachments added to semiautomatic rifles to make them fire continuously in the same way as automatic rifles.

And he said the way Congress has written the law, bump stocks don’t trigger the ban on machine guns.

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“A bump stock does not alter the basic mechanics of bump firing. As with any semi automatic firearm, the trigger still must be released and re-engaged to fire each additional shot,” he wrote.

Justice Sonia Sotomayor, writing the dissent for the three Democratic appointees, said Justice Thomas was dissecting definitions too finely. She said bump stocks seem like machine guns to her.

“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,” she wrote.

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SEE ALSO: Cargill celebrates bump stock victory at Supreme Court: ‘This is huge for everyone in America’

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An automatic weapon, or machine gun, is one that fires continuously as long as the trigger is pulled.

Machine guns are heavily regulated, both in terms of supply and who is permitted to own one.

A bump stock is a device that attaches to the rear of a rifle, helping it slide quickly back and forth. The resulting motion helps repeatedly engage the trigger fast enough that it can simulate automatic fire.

Justice Thomas said the case hinges on the law’s definition of “a single function of the trigger” as the key to defining an automatic weapon. He said even with bump stocks, a rifle still requires the right amount of pressure from the non-trigger hand on the barrel.

“Without this ongoing manual input, a semiautomatic rifle with a bump stock will not fire multiple shots. Thus, firing multiple shots requires engaging the trigger one time — and then some,” he wrote.

He pointed out that the Bureau of Alcohol, Tobacco, Firearms and Explosives had repeatedly declined to define bump stocks as machine guns. That changed after the 2017 Las Vegas massacre, in which a gunman using bump stocks fired down on a concert from a hotel, killing 58 people and wounding more than 500 others.

That attack loomed large in the arguments before the court, and the justices’ rulings.

“All the shooter had to do was pull the trigger and press the gun forward. The bump stock did the rest,” Justice Sotomayor said.

But Justice Samuel A. Alito Jr., who joined the majority, said tragedies can’t trump the law.

“The horrible shooting spree in Las Vegas in 2017 did not change the statutory text or its meaning,” he wrote. “There is a simple remedy for the disparate treatment of bump stocks and machine guns. Congress can amend the law — and perhaps would have done so already if ATF had stuck with its earlier interpretation. Now that the situation is clear, Congress can act.”

The case was brought by Michael Cargill, owner of Central Texas Gun Works, who challenged the ATF’s 2018 rule reversal.

The 5th U.S. Circuit Court of Appeals ruled in his favor, reasoning that the government’s use of a decades-old ban on machine guns and applying that to bump stocks was ambiguous.

The Supreme Court’s decision affirms that ruling.

“This is huge for the Second Amendment community. This is huge for everyone in America. If you’re pro-gun, or anti-gun, it doesn’t matter. This is about the administrative agency,” Mr. Cargill told The Washington Times, adding that an agency can’t write laws.

“It has to go back to Congress. Congress has to write the law.”