How “bump-stock” devices work

The deadly arsenal of weapons found in a 32nd-floor room at the
La Vegas Mandalay Bay Hotel included 16 assault rifles, 12 of which had been modified from semi-automatic to fire in automatic mode

Semi-automatic: One round fired each time trigger is depressed.
Rate of fire limited to speed shooter can squeeze trigger

Bump stock: Sliding shoulder rest replaces rifle’s fixed stock and pistol grip and fits over receiver extension (buffer tube)

Automatic: When trigger is depressed gun fires continuously until magazine is empty. Rate of fire can reach over 500 RPM
Buffer tube: Buffer spring uses recoil to recycle bolt, eject spent case and load next round from magazine

2  RECOIL
FOWARD MOTION
1    3
Trigger step

1. Shooter holds unmoving finger on trigger step and pushes gun forward to fire first round
2. Recoil pushes rifle, including trigger, backwards into bump stock
3. Buffer spring pushes rifle forwards,
hitting trigger repeatedly against trigger finger. Shooter can achieve something close
to automatic fire

Magazine: Typical 30-round magazine can be emptied in around 5-7 seconds


Sources: Slide Fire Solutions, Daniel Defense    © GRAPHIC NEWS