Mobile for a long time, and that is why it is considered one of the meta SMG picks of all time. Its lightweight frame gives ...

WATCH: Up close and personal with the bump stock: 'Machine gun' or firearm toy? ABC News Live Prime, Feb. 27, 7 p.m. and 9 p.m. ET, streaming on Hulu or the ABC News app.

What makes a gun 'automatic'? Bump stocks combine two legal devices, a plastic stock and a firearm, that together function like a machine gun. The bump stock harnesses the recoil of the rifle to ...

In this Oct. 4, 2017 file photo, a device called a "bump stock" is attached to a semi-automatic rifle at the Gun Vault store and shooting range in South Jordan, Utah. The U.S. Supreme Court ...

The gunman used 22 semiautomatic rifles, 14 of them equipped with bump stocks. Related The Justice Department had long taken the view that bump stocks fell outside a federal law banning machine guns.