In her scathing dissent, liberal justice Sonia Sotomayor accused her conservative colleagues of ignoring bump stocks' ability to transform semiautomatic firearms into much more powerful and deadly weapons.

"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," Sotomayor wrote. "A bump-stock-equipped semiautomatic rifle fires automatically more than one shot, without manual reloading, by a single function of the trigger' ... Because I, like Congress, call that a machine gun, I respectfully dissent."

She expressed concern that the ruling would only contribute to more mass shootings, writing: "The majority's artificially narrow definition hamstrings the government's efforts to keep machine guns from gunmen like the Las Vegas shooter."