WASHINGTON — The National Rifle Association on Thursday opened the door to supporting a narrowly crafted restriction on a type of gun accessory used in the Las Vegas massacre, easing slightly its historically staunch opposition to gun regulations.
The move was a stunning shift for an organization that has bitterly fought any new gun control rules for years. It indicated how much traditional gun-rights advocates have been put on the defensive since Sunday night’s attack that killed 58 people and injured hundreds more during a country music concert.
The gunman apparently used a device called a bump stock to alter his semiautomatic assault rifles so they would fire nearly as rapidly as a machine gun. Authorities said they found 12 bump stocks among the arsenal of 23 weapons in his hotel room.
The Bureau of Alcohol, Tobacco, Firearms and Explosives ruled in 2010 that bump stocks were legal because they do not alter the inner workings of a gun and therefore do not fall under the government’s ban on machine guns. Rather, bump stocks use the energy from a weapon’s recoil to rapidly and repeatedly put pressure on the trigger.
Many pro-gun Republicans in Congress, cautioning they do not want to open debate to other gun control measures, have said this week they were shocked by the murderous use of bump stocks in Las Vegas and said they are willing to consider a ban. A White House spokeswoman said Thursday that President Trump also is willing to discuss restrictions, but did not provide details.
The NRA, which is the nation’s largest pro-gun lobby, on Thursday requested a review of bump stocks and past rulings by the ATFE. Such a review could take weeks or months and could blunt momentum in Congress for quick legislation.
“The NRA believes that devices designed to allow semiautomatic rifles to function like fully-automatic rifles should be subject to additional regulations,” according to a statement sent Thursday afternoon from Wayne LaPierre, the NRA’s executive vice president, and Chris Cox, the group’s top lobbyist.
The NRA statement was the first comment from the group since the mass shooting. Gun-rights supporters are not uniformly in favor of restrictions on bump stocks, and it’s unclear whether the NRA will commit to supporting a full ban.
“Adding additional laws might feel good for some people, but it does nothing to solve the problem,” said Wayne Ross, an Alaska lawyer and NRA board member since 1979.
Ross said he has no problem with the NRA’s official position, which was issued after he spoke with the Globe. He doesn’t use a bump stock.
“A guy that buys one of those things would buy it for the fun of it, for the most part,” Ross said. “Hunting would not be a reason, unless you get attacked by a grizzly bear and you want to shoot it a lot.”
In the past, after mass shootings in Newtown, Conn., and Orlando, the emotional response has faded, relieving pressure on Republicans in Congress to make changes.
“This is a typically savvy way of kicking the ball to an ineffective government agency rather than simply advocating for the obvious solution which is, ‘Let’s ban these things,’ ” Mark Glaze, the cofounder of Guns Down, an advocacy group pushing for stronger gun control, said of the NRA statement.
“This is far from the biggest problem we face on guns,” added Glaze. “Of course Congress should ban these. But it’s like throwing a drop of water at a burning house.”
He noted that the gunman in last year’s Orlando mass shooting, where 49 people died, was able to kill that many people without using a bump stock.
But the NRA statement rang out clearly to Republicans across the country.
“If the NRA comes out and says, ‘It should be outlawed or banned,’ then they will pass it,” predicted Seth Weathers, a political consultant to Michael Williams, a Republican running for governor in Georgia.
The idea of even a limited new gun rule is already further fracturing the Republican Party.
Shortly after top White House aide Kellyanne Conway went on CNN to say that the Trump administration will “always welcome thoughtful conversation” on gun control, the right wing Breitbart News — run by her former White House colleague Steve Bannon — blasted Conway as “weak.”
Breitbart News also labeled members of the House GOP supportive of banning the bump stock devices as members of the “surrender caucus.”
Among gun enthusiasts, the mass killing and threat of illegality has only driven up interest in the devices.
“The phone has been ringing off the hook with people looking for them,” said Dana Ryll, the owner of Old Glory Guns & Ammo, in Mason, N.H. Ryll said he doesn’t have any more for sale and he has no plans to restock them.
“It was never a big-moving item. If someone asked for advice, like, ‘Should I get one?’ I’d say, ‘I wouldn’t,’ ” Ryll said.
Since the ATFE ruling during the Obama administration, the devices have become easy to obtain for as little as $99 and are widely marketed as adding an additional thrill for fans of high-powered rifles. But the devices make a weapon less accurate.
“It’s more of a toy than anything else,” said Steven Howard, a gun and firearms expert based in Michigan. “The reason this guy was so successful was that he was shooting at something the size of a football field.”
In 2010, a Texas-based company called Slide Fire sought permission from the ATFE for permission to sell the devices.
Slide Fire’s justification, documents show, was that the bump stock would help people “whose hands have limited mobility’’ fire an AR-15 military style rifle.
“The stock has no automatically functioning mechanical parts or springs and performs no automatic mechanical function when installed,” said the 2010 ATFE letter green-lighting Slide Fire’s product. “Accordingly, we find that the ‘bump-stock’ is a firearm part and is not regulated as a firearm under the Gun Control Act or the National Firearms Act.”
Slide Fire, which didn’t respond to a request for comment, says on its website that it has currently suspended sales of the item.
A sound analysis from The New York Times suggests the modification allowed Las Vegas gunman Stephen Paddock to fire about 90 rounds in 10 seconds, about the rate of a fully automatic weapon. For comparison, the gunman in the Orlando nightclub shooting was able to fire 24 rounds in about nine seconds, the Times analysis shows.
Senator Dianne Feinstein of California was among Democrats who introduced bills to ban the device.
Howard, the Michigan gun expert and lawyer, said he feels Congress should not act to ban bump stocks.
For one, Howard said there are other ways to retrofit a semiautomatic weapon to be able to fire more rapidly, which would still be legal even if bump stocks were not. Also, he said, so many have been sold since 2010 that it would be nearly impossible to rid the market of them.
“There’s too many out there,” he said. “If they restricted them when they first came out, it might have done some good. . . . Now it’s like trying to get rid of mosquitoes, you just can’t.”
Annie Linskey can be reached at firstname.lastname@example.org. Follow her on Twitter @annielinskey. Astead Herndon can be reached at email@example.com. Follow him on Twitter @asteadWH. Globe correspondent Julia Jacobs and Laura Crimaldi of the Globe staff contributed to this report.