This story was published in partnership with the Trace , a nonprofit newsroom covering gun violence in America. Sign up for its newsletter here .

On Jan. 29, in a federal courtroom in Mississippi, U.S. District Judge Carlton Reeves delivered a ruling that just a few years ago would have been unthinkable: He found the decades-old federal ban on machine guns unconstitutional.

At the center of the case was a firearm that seemed designed to provoke: an AR-15-style rifle named the “NFA Whore, Whore-16.” It had a switch that allowed its user to select between three modes of fire: “MARY” for safe, “SLUT” for semiautomatic, and “WHORE” for fully automatic machine gun. The defendant was also accused of illegally possessing 20 Glock “switches ”—devices that convert pistols to autom

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