The court split 6-3 along ideological lines in deciding that the federal government was wrong to classify a bump stock as a machine gun.
"A bump stock does not convert a semi-automatic rifle into a machinegun any more than a shooter with a lightning-fast trigger finger does," Justice Clarence Thomas wrote in his opinion for the majority.
Justice Sonia Sotomayor, who read the liberals' dissent from the bench, said the majority used an "artificially narrow definition" to reach a conclusion that will have "deadly consequences."