Officials with the U.S. Attorney’s office and the Bureau of Alcohol, Tobacco, Firearms and Explosives on Monday said they’re cracking down on the rising use of illegal machine gun-conversion devices. U.S. Attorneys from across the state held simultaneous press conferences, including one in San Antonio, to unveil “Operation Texas Kill Switch,” a statewide initiative targeting devices known as “switches” that can convert legally procured commercial firearms into a fully automatic weapon weapons that can fire more rapidly than some military-grade guns.