Las Vegas shootingKiller turned semi-automatic weapons into automatic ones – legally

Stephen Paddock’s shooting spree lasted about 12-14 minutes – but he was able to kill 59 people and wound more than 500. The reason: He used a technique called “bump stock” to turn two of his semi-automatic weapons into fully automatic ones, capable of firing between 500 and 800 rounds a minute.

Automatic rifles are heavily regulated and difficult to buy in the United States, but the perfectly legal bump stock method allows would-be mass shooters to circumvent the automatic weapons ban.

Newsweek reports that there have been numerous attempts in recent years to outlaw bump stocking, but the NRA and the gun industry’s lobbyists successfully thwarted these efforts.

Senator Dianne Feinstein has been on the forefront of the fight to ban bump stocking. She told the AP several years ago that she was concerned about the emergence of new technologies that could retrofit firearms to make them fully automatic. 

“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,” she said. 

The user of a semi-automatic weapon must pull the trigger for each round fired. With a fully automatic firearm, one pull of the trigger unleashes continuous rounds until the magazine is empty. 

The United States has heavily regulated the purchasing of fully automatic weapons since the early 1930s – the heyday of spectacular bank robberies and prohibition-related gang warfare.

In 1986, President Ronald Reagan pushed for, and Congress passed, an amendment to the federal National Firearms Act, which further restricted the transfer or possession of machine guns by civilians. The amendment contained a grandfathering clause which allowed the sale and transfer of previously manufactured and registered automatic weapons.

Newsweek notes that there had been several attempts to retrofit semi-automatic weapons so that they would become fully automatic weapons and still comply with the 1986 law – but until recently, such attempts were not successful.

This changed a few years ago when the bump stock – also called “slide fire” — was invented.

The bump stock, which costs under $100, in effect replaces the gun’s shoulder rest with a “support step” that covers the trigger opening. The shooter holds the pistol grip with one hand and pushes forward on the barrel with the other, squeezing the trigger. The recoil activates a spring mechanism inside the device, causing the gun to buck back and forth, “bumping” the trigger. The shooter has to squeeze and hold the trigger only once to initiate the process, just as he or she would do with a fully automatic weapon.

This means that, technically, the shooter must use his finger to pull the trigger for each round fired, thus keeping the weapon within the legal definition of a semi-automatic weapon. In effect, however, the shooter squeezes and holds the trigger only once – the bump stock’s spring mechanism does the rest.

Paddock had 23 different weapons in his hotel room, and officials told the AP that he had bump stocks attached to two semi-automatic guns.

There are other ways – the trigger crank and the auto-sear — to turn a semi-automatic weapon into a fully automatic one. Both mechanisms can be purchased online for under $50 – but both would be illegal because they more permanently turn the semi-automatic weapon into an automatic one. A trigger crank, also called “gat crank,” bolts to the trigger guard of a semi-automatic and allows the user to fire the weapon considerably more often by engaging the trigger more quickly. An auto-sear, which costs under $50, holds the hammer back under the tension of the mainspring. When the trigger is pulled, the sear moves out of its notch, releasing the hammer and firing the gun.