Bump stocks can turn a semiautomatic weapon into a firearm that shoots at nearly the speed of a machine gun, and a "machine gun" is what the devices will be considered going forward. NPR reports the Trump administration on Tuesday announced a ban on the attachments, a move facilitated by the devices' reclassification as "machine guns"—they'll then be covered by the federal law that prohibits the guns. It'll take about 90 days for the regulation to go into effect, and it doesn't just impact the sale of new devices: Those who possess the attachment—tens of thousands are estimated to exist—will need to destroy them or hand them over to the ATF before the 90 days are through.
The move is the culmination of President Trump's March announcement that the devices would be banned; 14 of them were infamously attached to weapons found in the hotel room from which Stephen Paddock unleashed the October 2017 Las Vegas massacre. The Wall Street Journal reports the Justice Department says the redefinition has passed a legal review that attorneys with the ATF participated in—notably, as the ATF in 2010 determined bump stocks weren't machine guns. The DOJ says it is ready to fight any legal challenges that may arise, and they almost certainly will. The AP reports Gun Owners of America vowed to file a suit. The Washington Examiner's take is that the move is the right one, but not one that will really impact future mass shootings, as the devices reduce a gun's accuracy. The Las Vegas shooting was a special case due to the shooter's distance (1,200 feet) and angle (shooting from above).