The National Rifle Association recently came out in support of regulating bump stocks, but there’s a catch. Stephen Paddock killed 58 people, and injured more than 500 at a country music concert in Las Vegas recently. In the hotel room he made his base, police found 12 rifles outfitted with the controversial attachment. The NRA wants them further examined, but not for the reasons one might expect.

What are bump stocks?

A bump stock device, (left) fits on a semi-automatic rifle to increase the firing speed, making it similar to a fully automatic rifle. | George Frey/Getty Images A bump stock device, (left) fits on a semi-automatic rifle to increase the firing speed, making it similar to a fully automatic rifle. | George Frey/Getty Images

According to The New York Times, a “bump stock” replaces a rifle’s standard stock, or the part held against the shoulder. It allows the weapon to slide back and forth rapidly, harnessing the energy from the kickback. The stock “bumps” back and forth between the shooter’s shoulder and trigger finger. That causes the rifle to rapidly fire up to 400-800 rounds per minute.

“The classification of these devices depends on whether they mechanically alter the function of the firearm to fire fully automatic,” said Jill Snyder. She serves as special agent in charge at the Bureau of Alcohol, Tobacco, Firearms and Explosives. “Bump-fire stocks … do not actually alter the firearm to fire automatically, making them legal under current federal law.”

The accessories’ capabilities, not classification, recently came under fire.

Why the NRA wants them regulated

Senator. Dianne Feinstein points to a photograph of a rifle with a “bump stock.” | Chip Somodevilla/Getty Images Senator. Dianne Feinstein points to a photograph of a rifle with a “bump stock.” | Chip Somodevilla/Getty Images

Stephen Paddock’s use of the devices to augment his weapons’ firing speed brought them back to legislative attention. In the Senate, Democrat Dianne Feinstein introduced a bill that would make them illegal. Representative Carlos Curbelo, a Republican, also introduced a bipartisan bill banning them. In a departure from its past positions on gun control, the NRA agreed with part of the effort.

“The NRA believes that devices designed to allow semi-automatic rifles to function like fully-automatic rifles should be subject to additional regulations,” NRA CEO Wayne LaPierre and executive director of the NRA Institute for Legislative Action Chris Cox said in a joint statement. “The National Rifle Association is calling on the Bureau of Alcohol, Tobacco, Firearms and Explosives … to immediately review whether these devices comply with federal law.”

The NRA stopped short of advocating legislative action. What it does want is an examination of a current law on the books.

Bump stocks are legal, but real automatic weapons aren’t

A Rock River Arms AR-15 rifle with ammunition | Joe Raedle/Getty Images A Rock River Arms AR-15 rifle with ammunition | Joe Raedle/Getty Images

One of the legal instruments the NRA wants examined is the Firearms Owner Protection Act. That legislation banned fully-automatic guns manufactured after May 1986 from sale to civilians.

According to the ATF, in 1986, this act amended the National Firearms Act. That prohibits the transfer or possession of machine guns. Exceptions exist for transfers of machine guns to, or possession of machine guns by, government agencies, and those lawfully possessed before the effective date of the prohibition, May 19, 1986. That means antique guns and collector’s items stay in their owners’ legal hands, and some owners got grandfathered in.

The NRA has not specified whether it wants the ATF to add an amendment to that act specifying bump stocks. For some legislators, the ability of the accessory, and not its definition, make a difference.

Even gun owners don’t recognize these devices

Senior sales staff Mark Warner shows a bump stock installed on an AR-15 rifle. | Jim Watson/AFP/Getty Images Senior sales staff Mark Warner shows a bump stock installed on an AR-15 rifle. | Jim Watson/AFP/Getty Images

Majority Whip John Cornyn of Texas, the second-ranking Senate Republican, dispatched his staff to research the use of bump stocks. He told Politico he considers it “worthwhile” to hold a hearing on the topic.

“It is ordinarily illegal to transform a semi-automatic weapon into an automatic weapon, and it’s illegal to buy an automatic weapon unless you have a special license and undergo a special background check,” he said. “I’m not sure how these bump stocks fit into that scheme.”

Other pro-gun lawmakers said they just learned of the accessories. John Thune of South Dakota said he talked to other GOP lawmakers about them and several expressed interest in finding out more about how the devices are used. “I think it’s something we ought to look into,” he said. “I don’t know a lot about them, and I’m somebody who … is fairly familiar with a lot of firearms.”

Texas Rep. Bill Flores, a gun owner, told The Hill, “There’s no reason for a typical gun owner to own anything that converts a semi-automatic to something that behaves like an automatic.”

Some legislators questioned how the devices came into legality in the first place. The ATF itself flip-flopped on the idea several times.

Before bump stocks, another accelerator hit the market

A bump stock device (left) fits on a semi-automatic rifle, similar to previous devices. | George Frey/Getty Images A bump stock device (left) fits on a semi-automatic rifle, similar to previous devices. | George Frey/Getty Images

The ATF approved the devices for sale in 2010, NPR reported. “It’s a goofy little doodad,” said Rick Vasquez, the former firearms official who first signed off on a recommendation that the ATF need not regulate the devices. Before bump stocks, the ATF did outlaw another, similar device.

The Associated Press reported that a former Marine, Bill Akins, created a similar mechanism two decades before bump stocks. He wanted to create something that harnessed a gun’s recoil, to fire bullets at a similar rate to automatics.

“For decades, gun owners had been bracing guns against their hips to increase the rate of their trigger pulls,” the AP reported, “a technique known as ‘bump firing.’” In 1996, Akins built an attachment that did the same. He received a patent for the Akins Accelerator in 2000 and began selling it.

The ATF initially ruled that, since the Accelerator did not modify a firearm’s ability to shoot multiple rounds per trigger, it did not warrant automatic classification. Then, in 2006, the agency reversed itself and ordered Akins to stop selling it. The ATF said the initial device it tested had misfired, and the agency then determined its use of a spring effectively made it a machine gun — a modification regulators deemed illegal.

After the ATF ruled in favor of bump stocks, Akins sold his patent to another company, which engaged in litigation with the company that made bump stocks. He said he remains bitter about the entire situation. “[The ATF] cost us hundreds of thousands of dollars and destroyed my company,” he said.

When the inventor of bump stocks submitted its patent, the agency stuck with its initial ruling.

Bump stocks became legal — and stayed that way

Assault rifles hang on the wall for sale at Blue Ridge Arsenal. | Jim Watson/AFP/Getty Images Assault rifles hang on the wall for sale at Blue Ridge Arsenal. | Jim Watson/AFP/Getty Images

The original bump stock company, Slide Fire, was started by an Air Force veteran in Texas. He said he created the device to help gun users who “weren’t able to fire as fast as we wanted.” The Boston Globe reported the stocks have their challenges.

“It’s very difficult to control except under perfect conditions,” said Steven Howard, a gun and firearms expert based in Michigan. He called it “more of a toy that anything else.

“The reason [Paddock] was so successful was that he was shooting at something the size of a football field.”

Bump stocks originally went on the market as mobility devices, although Slide Fire’s current website makes no mention of that usage. Slide Fire, told the ATF the bump stock helps 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 a 2010 letter from the ATF signed by John R. Spencer, head of the firearms technology branch. “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.”

Even though the NRA wants them evaluated further, enthusiasts have a different response.

After Las Vegas, bump stocks hit unprecedented popularity

A young attendee inspects an assault rifle during the 2013 NRA Annual Meeting and Exhibits in Houston, Texas. | Justin Sullivan/Getty Images A young attendee inspects an assault rifle during the 2013 NRA Annual Meeting and Exhibits in Houston, Texas. | Justin Sullivan/Getty Images

Slide Fire’s website claims the manufacturer has run out of the devices due to unprecedented orders. Gun resale websites and dealers said the same, and that bump stocks now sell for triple their value. Howard said banning them today makes little sense. “Only thing you’re going to succeed in doing is making criminals out of people who weren’t criminals in the first place,” he explained. First, other ways exist of turning a semiautomatic weapon into a more rapidly firing one.

“Converting a semi-automatic to fully automatic is very, very easy,” John Sullivan, lead engineer for the gun access group Defense Distributed, told Wired. “At the end of the day, machine guns are easy to make.”

Howard also noted that Slide Fire has sold so many since 2010, it’s nearly impossible to get rid of them now.

“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.”

Regardless, skepticism about their usage abounds.

Even the NRA bans bump stocks

Even the NRA bans bump stocks and similar devices at its gun range. | Scott Olson/Getty Images Even the NRA bans bump stocks and similar devices at its gun range. | Scott Olson/Getty Images

The NRA actually bans them from its own firing range at NRA headquarters, due to safety concerns, Politico reported. Firing ranges often limit the rate at which guns can fire for safety reasons, especially for untrained users. Paul Valone, president of pro-gun rights Grass Roots North Carolina, said automatic weapons are also often banned.

“If someone is not trained to fire rapidly they may miss, frankly, and hit things like the ceiling of the range and other areas which could cause damage and safety issues,” Valone said. He called bump stocks “useless” for target practice. “Because it’s notoriously inaccurate, it’s really not a threat to anybody except in one, and only one, circumstance, and that’s when you’re on the 32nd floor of a building shooting into a mass of people,” Valone said.

Others, however, think any regulation creates a slippery slope.

Erich Pratt, executive director of Gun Owners of America, gave his take on how Congress should view the issue, NPR reports. “They’ll start asking questions about why anybody needs this, and I think the answer is we have a Bill of Rights and not a Bill of Needs,” Pratt said.

Whether Feinstein and Curbelo’s bills make it to the floor remains in question. After the Sandy Hook shooting, Feinstein proposed similar legislation that never even made it to a vote. The NRA may not be ready to condone legislative action against these accessories, but its reservations at least might give some enthusiasts pause before buying similar devices.

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