It is unclear yet which of the 23 guns Las Vegas shooter Stephen Paddock used when he killed at least 59 people and injured more than 500. Audio recordings from the scene strongly suggest that at least one of the guns was a fully automatic weapon or had been re-fashioned to operate like one.
Witnesses said the barrage Paddock unleashed from his 32nd-floor hotel room sounded like a “machine gun” and audio analysis from The New York Times comparing the Las Vegas sound to the semi-automatic rifle used in the Pulse nightclub shooting in 2016 appears to show a weapon with automatic capabilities.
Officials say 12 of Paddock’s rifles were outfitted with “bump stocks”—a legal but controversial add-on that essentially converts a semi-automatic weapon into a fully automatic one.
“This replacement shoulder stock turns a semi-automatic rifle into a weapon that can fire at a rate of 400 to 800 rounds per minute,” California senator Dianne Feinstein, who is a vocal opponent of the add-on, once explained in an interview with the AP.
Here’s how Wired succinctly describes the way a bump stock works:
That device adds a spring mechanism to the part of the rifle that presses into a shooter’s shoulder, so that the entire rifle bounces forward with every detonation of a round of ammunition. The shooter merely holds his or her trigger finger in place, and that bouncing pulls the trigger again and again at a rate that approximates machine gun fire
The devices do result in lower accuracy, since they cause the shooter to jolt. (If Paddock was using them, it probably did not make his attack less deadly, since he seemed to have been firing indiscriminately into the large crowd.)
Semi-automatic weapons—in which one trigger pull fires one bullet—are mostly legal in the United States, and were used in mass shootings in Aurora, Colorado, Newtown, Connecticut, among others. Bump stocks are also essentially legal, and available, and Nevada does not restrict purchases of large capacity magazines.
The AP reports some stores are already seeing increased interest in bump stocks, which were originally intended to help people with disabilities fire guns. Republican and Democratic lawmakers expressed concern about the devices following the shooting, NBC reported, but proponents of gun control in Congress are pessimistic about the chances of any new legislation.
Bump stocks are not the only way a weapon can be modified to shoot multiple rounds with one pull of the trigger. Special cranks that can be attached to a semi-automatic rifle to allow continuous fire, and some use simple rubber bands to achieve this effect. You can legally own an actual machine gun as well: A federal regulation bans all automatic weapons for civilians, except those manufactured before 1986—and these have to be registered with the government.
What’s more, as Wired points out, it’s very easy—and illegal—to turn a semi-automatic weapon into an automatic one, with just a few minutes of work.