Explained: the gun modification that helped make Las Vegas' shooting America's deadliest

Explained: the gun modification that helped make Las Vegas' shooting America's deadliest
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When police raided the suite on the 32nd floor of the Mandalay Bay hotel used by Las Vegas shooter Stephen Paddock, they found 23 firearms, including 12 rifles with “bump stock” modifications.

The discovery has prompted debate over whether the device, which has been credited with helping to make the shooting the deadliest in modern US history, should be banned.

While having long resisted gun controls, senior Republicans in Congress have indicated that they are open to banning the modification, and the National Rifle Association has said it would support tighter restrictions.

But what are “bump stocks” and how do they work?

What are they?

“Bump stocks” are attachments that can be added to semi-automatic rifles, allowing them to mimic fully automatic gun fire.

How do they work?

The device is fitted in the place of a rifle’s standard stock – the part held against the shoulder.

It frees the weapon to “bump” back and forth between the shooter’s shoulder and the trigger finger, using energy from the kickback when the weapon fires.

This means that when the shooter holds the trigger, the rifle fires repeatedly at nearly the rate of a machine gun – far faster than an unaided finger could pull a trigger.

Why are they currently legal?

While it is illegal for private citizens to have fully automatic firearms manufactured after May 19, 1986, and they are required to have a licence for earlier models, “bump stocks” are not banned under US federal law.

“The classification of these devices depends on whether they mechanically alter the function of the firearm to fire fully automatic,” Jill Snyder, a special agent in charge at the Bureau of Alcohol, Tobacco, Firearms and Explosives, said at a press conference in Las Vegas on Tuesday.

“Bump-fire stocks, while simulating automatic fire, do not actually alter the firearm to fire automatically, making them legal under current federal law.”

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