More than a year after the Las Vegas massacre — the deadliest modern mass shooting in America — the Trump administration is using existing law to ban bump stocks, attachments that turn semi-automatic rifles into automatic weapons. The updated rule by the Bureau of Alcohol Tobacco Firearms and Explosives (ATF) “clarifies that bump-stock-type devices are machineguns,” which have been outlawed for decades.

Firing from the 32nd floor of the Mandalay Bay hotel on the Las Vegas strip, Stephen Paddock affixed bump stocks to his rifles for his attack on the Route 91 Harvest music festival in October 2017. He killed 59 people and wounded more than 400 others. The new regulation makes plain that the Las Vegas massacre inspired the re-consideration and ban of the devices, which had previously been approved for sale by ATF, including under the Obama administration.

A bump stock replaces the fixed stock at the back of a semi-automatic rifle. As the rifle fires, the bump stock absorbs and then rebounds the recoil, pushing the gun slightly forward into the shooter’s otherwise immobile trigger finger, causing the gun to fire again and again and again without an additional “pull” of the trigger. Because a bump-stock device “automatically re-engages the trigger finger,” ATF has concluded, it is outlawed under laws dating from the 1930s and 1980s.

The administration revealed final regulatory language Tuesday, banning the devices roughly 90 days from now. Existing owners will not be compensated — they must either destroy their bump stocks or surrender them at a local ATF office. “Options for destroying the devices include melting, crushing, or shredding,” the rule advises. With plastic bump stocks, “individuals can use a hammer to break apart the devices.” A cost estimate, included with the rule, anticipates that owners will have to destroy as many as 500,000 bump-stocks, worth approximately $100 million. (The devices currently retail at prices ranging from $100 to $425.)

The NRA has been atypically muted in its response to the new rule. The gun lobby had previously backed a federal review to see if bump-stocks complied with existing law, writing: “The NRA believes that devices designed to allow semi-automatic rifles to function like fully-automatic rifles should be subject to additional regulations.” On Tuesday, NRA spokesperson Jennifer Baker expressed mild concern, called the final rule “disappointing” and suggesting the administration should have carved out an “amnesty” for “law-abiding Americans who relied on prior ATF determinations” that the devices were legal to buy.

Why is the NRA not kicking and screaming — or suing? The organization has long touted the distinction between civilian semi-automatic rifles and military guns with fully-automatic capability as the reason civilians should be able to own weapons like the AR-15. The sale of devices like bump stocks that put automatic-fire capability in the hands of the masses had threatened to undermine decades of public marketing and court arguments. Those arguments, however, are not on the level. The unpleasant truth is that semi automatic fire is more accurate than automatic fire. The military instructs soldiers use semi automatic fire in nearly all combat scenarios. And some experts believe Paddock could have killed more people if he’d not used a bump stocks to spray the concert, and instead had targeted his shots into the crowd.

The new bump-stock rule is already facing legal challenges. A lawsuit brought by the Firearms Policy Coalition argues that bump stock owners must be compensated for devices that ATF had previously ruled legal: “ATF’s abrupt about-face on this issue..smacks of agency abuse or dereliction of duty in following the law.”

This suit also puts to a test the authority of Acting Attorney General Matthew Whitaker, who executed the rule. Whitaker’s appointment by President Trump to act in the stead of Jeff Sessions, who resigned in November, has been challenged as contrary to law that indicates Deputy Attorney General Rod Rosenstein should have moved into the acting role. (Trump has nominated former attorney general William Barr has as a permanent replacement.)

“Defendant Matthew Whitaker is unable to lawfully perform the duties and responsibilities of Attorney General,” the suit argues. “Since he lacks the authority to sign the Final Rule as Attorney General, the Final Rule must be struck down as invalidly enacted.”