ATLANTA (AP) — The Las Vegas gunman possessed a little-known device called a "bump stock" that was not widely sold — until now.

Originally created with the idea of making it easier for people with disabilities to shoot a gun, the attachments allow a semi-automatic rifle to mimic a fully automatic weapon by unleashing an entire large magazine in seconds. Now the deadliest mass shooting in modern U.S. history has drawn attention to the devices, which critics say flout federal restrictions on automatic guns.

The stocks have been around for less than a decade. The government gave its seal of appro...