'Bump fire' devices turn rifles into machine guns: How is that legal?

The heated public debate over gun control can hardly be described as nuanced. Yet one perfectly legal product that turns a regular rifle into a machine gun highlights how it's often the fine print that defines not only what kind of guns Americans can own, but how they're allowed to work, and how they can be used.

A defense of assault-style rifles like the AR-15 used in the Sandy Hook massacre is that they're basically just semiautomatic rifles with cosmetic improvements. In other words, each bullet needs an individual trigger pull in order to explode out of the barrel. Actual spray-trigger machine guns, after all, have been illegal on the civilian market since 1986.

But debate around so-called bump fire devices that "simulate" automatic fire by utilizing a rifle's recoil to shoot the next bullet have caused some to wonder whether the devices could inspire a bureaucratic reclassification of assault weapons into machine guns, which in turn could lead to a de facto ban without Congress getting involved. That question may be politically sharper now, especially since an all-out assault weapons ban, according to University of Virginia political scientist Larry Sabato, is "dead in the water."

"If the ATF [the US Bureau of Alcohol, Tobacco, Firearms and Explosives] wants to now come and ban [bump-fire devices], they basically have to modify the definition of a machine gun," Jeremy Cottle, an Iraq War veteran and inventor of the Slide Fire stock, told the Guns America blog.

How much do you know about the Second Amendment? A quiz.

On sale at the Lawrenceville, Ga., Gun Show last weekend, one such bump-fire device is known to shake poorly built rifles apart from the racket they make. A video accompanying the small metal trigger device showed an assault-style rifle pumping out dozens of rounds in seconds. It retailed for $49.95.

To be sure, the ATF has been paying close attention to the devices, and have delineated a narrow line of legality based, in essence, on mechanics versus physics.

Assault-style weapons can't be mechanically customized to spray-fire, but a nonmechanical device that simply aids the shooter's own firing action remains on this side of legal, according to ATF.

In 2005, the ATF rescinded a "letter of legality" given to one such device, the Akins Accelerator, mostly because the actual product didn't match the model sent to the ATF for approval.

But the problem also arose from a mechanical spring used in the original Akins. The product, springless, is now on sale again, certified by ATF.

Reviewing Mr. Cottle's Slide Fire, a Guns America blogger noted last year, "There isn’t going to be any way to get around what this thing does and I think it is best to call it what it is," he writes. "The Slide Fire is a $369 replacement stock for your AR-15 that when used properly, simulates automatic fire."

“The Slide Fire simply allows you to shoot as fast as you want to,” Cottle told Guns America. “You can shoot one round, 2 rounds, 3 rounds, 15 rounds or a full magazine.… There are no moving parts in the Slide Fire and no springs. You hold your finger on the trigger rest and push forward to fire the gun. It is not automatic. Nothing is automatic. You actively fire every round, and if you stop pushing forward or you take your finger off the trigger the gun stops firing. It just helps you fire the gun in semi-automatic very fast."

So far, for gun owners, the bump-fire devices are largely regarded as cool toys, and salesmen were cutting prices on the devices at the Lawrenceville Gun Show in order to move them.

As one Internet commenter said, "It's a fun toy, but nowhere near as impressive as the advertisements for it will lead you to believe. No surprise really. Hence the reason why the law enforcement and security community is NOT rushing out to buy such stocks for their semi-auto rifles."

But that machine gun capability is so easily, and legally, acquired also highlights to some experts how little most Americans know about gun culture, and, for that reason, how difficult a task it can be to legislatively curb Second Amendment rights. President Obama has already focused much of his gun safety push on executive orders, in a nod to the near-impossibility of getting Congress to seriously address new gun-control measures.

"The fact is, in a lot of cases we overstate how much people know about [gun-control policies], because most don't follow the details of pending legislation closely," says Brendan Nyhan, a political science professor at Dartmouth College, in Hanover, N.H.

But even within American gun culture, specific products and policies are up for debate, he notes. "The open-minded gun owner may express a different opinion on a bundle of proposals to restrict gun rights versus a specific proposal," such as limiting assault weapons, says Mr. Nyhan.

Well aware of the implications of bump-fire devices, gun salesmen are quick to tout that the ATF has given the thumbs-up. "Nobody can predict what the ATF is going to do about anything, but from our side we have done everything by the book," Cottle, the Slide Fire inventor, told the gun blog.

How much do you know about the Second Amendment? A quiz.