A divided Supreme Court on Friday struck down a federal ban on bump stock devices that allow semiautomatic rifles to fire hundreds of bullets a minute, upending one of the few recent efforts by the federal government to address the nation’s epidemic of gun violence.

The 6-3 ruling along ideological lines continues the conservative majority’s record of limiting gun restrictions, most notably in a landmark 2022 ruling that has made it easier to challenge modern gun control laws. Friday’s ruling did not implicate the Second Amendment right to bear arms, but rather the Bureau of Alcohol, Tobacco and Firearms and Explosives’ interpretation of a law restricting machine guns.

In its ruling, the majority said bump stocks do not qualify as machine guns under a 1986 law that barred civilians from owning new versions of the weapons. The Donald Trump administration interpreted the law to ban bump stocks in 2018, after a gunman used the devices to open fire on a Las Vegas music festival, ultimately killing 60 people in the deadliest mass shooting in U.S. history.

In writing for the majority, Justice Clarence Thomas dove into technical aspects of the law and the mechanics of how the devices operate — including diagrams in his opinion — to explain the decision. The 1986 law defines machine guns as weapons that fire more than one shot “by a single function of the trigger.”

“With or without a bump stock, a shooter must release and reset the trigger between every shot,” Thomas wrote.

In an opinion concurring with Thomas, Justice Samuel A. Alito Jr. noted the carnage bump stocks had caused, but said Congress needed to amend the law if it wanted to outlaw them.

In a dissent read from the bench that indicated her concern about the majority’s finding, Justice Sonia Sotomayor said the majority eschewed a “straightforward” reading of the law. She was joined by fellow liberal Justices Elena Kagan and Ketanji Brown Jackson.

“By maintaining a myopic view focused on these mechanisms, the majority puts machine guns back in the hands of the people,” Sotomayor said.

Democrats and gun control groups quickly decried the ruling.

President Joe Biden called on Congress to ban bump stocks and pass an assault weapons ban, saying he would sign a bill immediately. Democratic Majority Leader Charles E. Schumer (D-N.Y.) called the ruling an “assault on public safety,” and others were even more blunt, noting that mass shootings had become tragically commonplace.

“More people are going to die because of the Supreme Court’s ruling,” said Douglas N. Letter, chief legal counsel at the gun control group Brady.

Others hailed the decision. Mark Chenoweth, president and chief legal officer of the New Civil Liberties Alliance that brought the case to the Supreme Court, said the ruling dealt with a single gun law but would have a broader impact.

“This case underscores the principle that agencies cannot regulate beyond their statutory authorization,” Chenoweth said. “I think the case will reverberate well outside the ATF context.”

After the Las Vegas shooting, the National Rifle Association said it was open to additional regulations on bump stocks. But following the court’s ruling Friday, an official with the gun rights group wrote on X that the justices had “properly restrained executive branch agencies to their role of enforcing, and not making, the law.”

Trump campaign spokeswoman Karoline Leavitt said in a statement that the court’s decision “should be respected.”

Michael Cargill, a U.S. Army veteran and the owner of a gun shop in Austin, challenged the ban after he was forced to surrender two bump stocks. He argued that ATF went too far when it reclassified bump stock-equipped rifles as machine guns in 2017 after public calls to ban the devices.

The agency previously ruled that it was legal to own bump stocks. Americans bought about 520,000 bump stocks between 2008 and 2017, while they were legal, according to figures from ATF.

Bump stocks are a piece of molded plastic or metal that replaces the butt of a rifle and the handle closest to the trigger. The piece allows that portion of the gun to slide freely back and forth. The recoil from a shot causes the gun to “bump” between the shooter’s shoulder and trigger finger, allowing rounds to be fired in quick succession.

Rifles equipped with bump stocks can fire an estimated 400 to 800 rounds per minute, a rate approaching that of automatic weapons.

Federal appeals courts were sharply divided on whether bump stocks meet the definition of a machine gun under the 1986 law in five earlier decisions on the ban’s legality, before the Supreme Court took up Cargill’s lawsuit in the case known as Garland v. Cargill.

The case was a test of the reach of a federal agency to enact and interpret regulations — a major theme in the current Supreme Court term. Other cases deal with the Securities and Exchange Commission, Consumer Financial Protection Bureau and a legal precedent that says courts should defer to agency interpretations of ambiguous statutes if they are reasonable.

The Biden administration defended the Trump administration’s interpretation that bump stocks are machine guns, arguing that the devices allow semiautomatic rifles to fire automatically with a single pull of the trigger. But attorneys for Cargill disputed that characterization, saying bump stocks are activated through repeated pulls of the trigger.

David Pucino, legal director of the Giffords Law Center, said the Supreme Court’s ruling could endanger bump stock bans in a handful of states that have laws that mirror the federal machine gun statute, but most of the prohibitions in about 15 states and D.C. would probably not be endangered because they address bump stocks directly.

Much of the oral arguments in the case in February were consumed by how bump stocks work. At one point, Kagan and Cargill’s attorney, Jonathan Mitchell, took turns using their hands to demonstrate what it looks like to fire a gun equipped with one of the devices.

Bump stocks were invented in the early 2000s, but the question of their legality has often shifted. In 2003, ATF said an early version was not a machine gun, but later revised its position to ban a version of the device that had an internal spring that aided firing. The agency again reversed course in 2008, approving a model without the spring.

During oral argument, Justices Neil M. Gorsuch and Brett M. Kavanaugh questioned the government’s evolving interpretation of whether bump stocks turned rifles into machine guns. Gorsuch added that he could understand why the government would want to ban the devices, but said Congress needed to explicitly do it.

Jackson and Kagan said bump stocks were the exact kind of weapons that Congress intended to ban with the 1986 machine gun law. In her opinion Friday, Sotomayor echoed the point.

“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.

Cargill filed his lawsuit challenging the ban in 2019, on the same day he surrendered his bump stocks to ATF.

A U.S. District Court dismissed Cargill’s claims and a three-judge panel of the conservative 5th Circuit Court of Appeals affirmed the ruling. The full 5th Circuit Court of Appeals then heard the case and reversed the decision. The Biden administration appealed that ruling to the Supreme Court.

In the meantime, the Supreme Court struck down a New York law that required a license to carry a gun in public in 2022. In that case, Thomas also wrote for the majority and established a major new test that required gun restrictions be consistent with the nation’s history of firearm regulations.

Gun advocates have since challenged dozens of regulations in the courts, arguing that they don’t have analogues in American history. The effort has resulted in a messy, unsettled landscape for gun regulations.

Some courts have upheld restrictions, while others have knocked down bans on “ghost guns,” high-capacity magazines, restrictions on the purchase of firearms by young adults and other provisions.

The Supreme Court has taken up another high-profile guns case this term, United States v. Rahimi. The high court is set to decide before the end of June whether people subject to domestic violence restraining orders have a constitutional right to possess guns.

The legal fights have played out at a moment of national anguish over gun violence and fierce debates about gun control.

Last year, there were 39 mass shootings in the United States, the highest number in any year since 2006, according to a Washington Post tracker. Another Post database found school shootings hit 46 in 2022, the most since at least 1999. A surge in homicides during the coronavirus pandemic also stirred concerns, although the trend has eased in most places.

Marianne LeVine contributed to this report.