Gunman had a 'bump-stock' device that could speed fire
The gunman who unleashed hundreds of rounds of gunfire on a crowd of concertgoers in Las Vegas had two "bump-stock" devices.
The devices could have converted semi-automatic firearms into fully automatic ones, officials said.
A semi-automatic weapon requires one trigger pull for each round fired. With a fully automatic firearm, one trigger pull can unleash continuous rounds until the magazine is empty.

https://www.cnbc.com/2017/10/03/gunman-had-a-bump-stock-device-that-could-speed-fire.html