Weapons

What Is a Bump Stock and How WasIt Used in the Las Vegas Shooting?

Twelve of the rifles the gunman in the Las Vegas mass shooting had in his 32nd-floor hotel room were each modified with a “bump stock,” an attachment that enables a semiautomatic rifle to fire faster.

The device replaces a rifle’s standard stock, which is the part held against the shoulder. It frees the weapon to slide back and forth rapidly, harnessing the energy from the kickback shooters feel when the weapon fires. The stock “bumps” back and forth between the shooter’s shoulder and trigger finger, causing the rifle to rapidly fire again and again. The shooter holds his or her trigger finger in place, while maintaining forward pressure on the barrel and backward pressure on the pistol grip while firing.