The justices heard arguments in an appeal by President Joe Biden's administration of a lower court's ruling in favor of Michael Cargill, a gun shop owner and gun rights advocate from Austin, Texas, who challenged the ban that was put in place after a 2017 mass shooting that killed 58 people in Las Vegas.
The Supreme Court, with a 6-3 conservative majority, has taken a broad view of gun rights, most recently in its landmark 2022 ruling striking down New York state's limits on carrying concealed handguns outside the home.
Some justices asked Justice Department lawyer Brian Fletcher to explain how a bump stock's features satisfy the definition of a machine gun.
"Intuitively, I am entirely sympathetic to your argument. I mean, and it seems like, yes, this is functioning like a machine gun would," said conservative Justice Amy Coney Barrett. "But, looking at that definition, I think the question is why didn't Congress pass that legislation to make this covered more clearly?"
The case centers on whether the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), a U.S. Justice Department agency, properly interpreted a law banning machine guns as extending to bump stocks. The rule took effect in 2019.
Machine guns are defined under a 1934 law called the National Firearms Act as weapons that can "automatically" fire more than one shot "by a single function of the trigger."
Conservative Justice Brett Kavanaugh noted that the two presidential administrations before Trump's had decided that rifles with bump stocks were not considered machine guns as defined by the statute at issue.
"That's reason for pause," Kavanaugh said.
Liberal Justice Ketanji Brown Jackson told Cargill's lawyer Jonathan Mitchell that Congress did not ban machine guns intending to focus on the mechanics of a trigger, but rather to capture weapons that achieve similar results.
"Why would Congress want to prohibit certain things based on whether the trigger is moving, as opposed to certain things that can achieve this lethal kind of spray of bullets?" Jackson asked.
Mitchell said that bump stocks lead to a "very high rate of fire, but it's not automatic."
Bump stocks use a semiautomatic's recoil to allow it to slide back and forth while "bumping" into the shooter's trigger finger, resulting in rapid fire. The devices allow a shooter to fire up to 800 bullets per minute, a rate comparable to machine guns issued to American soldiers, according to the U.S. Justice Department.
'A LITTLE BIT OF COMMON SENSE'
Liberal Justice Elena Kagan told Mitchell that a machine gun requires continuous pressure on a trigger, while a bump stock requires continuous pressure on a barrel.
"I can't understand how anybody could think that those two things should be treated differently," Kagan said.
"At some point, you have to apply a little bit of common sense to the way you read a statute," Kagan added.
Fletcher told the justices that weapons with a bump stock "do exactly what Congress meant to prohibit when it enacted the prohibition of machine guns" and that guns with these devices satisfy the statutory definition of a machine gun.
A rifle with a bump stock, Fletcher added, "fires more than one shot automatically - that is, through a self-regulating mechanism."
Conservative Justice Clarence Thomas questioned Fletcher about how to differentiate between firing a traditional machine gun such as an M16 rifle and a gun with a bump stock.
"Take an M16, you pull the trigger back and you hold it - and it keeps shooting. With a bump stock, you push forward and that both initiates and continues the firing," Fletcher said.
Federal law prohibits the sale or possession of machine guns, punishable by up to 10 years in prison.
Unlike many other gun rights cases, this one does not involve whether the measure violated the U.S. Constitution's Second Amendment right to keep and bear arms.
The United States is a country deeply divided over how to address persistent gun violence that Biden has called a "national embarrassment."
After a gunman used weapons outfitted with bump stocks in the shooting spree at a country music festival in Las Vegas, Trump's administration took action to prohibit the devices.
Cargill sued to challenge the rule, which required him to surrender his two bump stocks.
The New Orleans-based 5th U.S. Circuit Court of Appeals last year sided with Cargill in a divided opinion, concluding that the law did not unambiguously favor ATF's reading of the statute.
The Supreme Court has expanded gun rights in three major rulings since 2008. Its 2022 ruling recognized for the first time that individuals have a constitutional right to carry a handgun in public for self-defense, adopting a stringent test that makes it harder for gun regulations to survive a Second Amendment challenge.
