WASHINGTON (AP) — The National Rifle Association has joined the Trump administration and top congressional Republicans in a swift and surprising embrace of a restriction on Americans' guns, though a narrow one: to regulate the "bump stock" devices the Las Vegas shooter apparently used to horrifically lethal effect.

The devices, originally intended to help people with disabilities, fit over the stock and grip of a semi-automatic rifle and allow the weapon to fire continuously, some 400 to 800 rounds in a single minute. Bump stocks were found among the gunman's weapons and explain why victims in...