Add-ons let semi-autos fire like military weapons

BUNNLEVEL, N.C. — In the video, a shooter cradles a rifle equipped with a grenade launcher and 250-round magazine. But the star of this demonstration, posted online, is a deceptively low-tech plastic device that enables semi-automatics like this one to mimic the withering fire of weapons usually reserved for the military or police.

"FIRE AT WILL," invites the website of Slide Fire Solutions, a maker of the devices, known as slide or "bump" stocks. "Unleash 100 rounds, in 7 seconds."

Slide Fire pitched the device to federal regulators in 2010 as a way to help people with disabilities enjoy shooting sports. But it has become increasingly popular among able-bodied shooters looking for the rapid-fire thrill of obliterating their targets.

Now it is one of nearly 160 guns and accessories on U.S. Sen. Dianne Feinstein's hit list as she seeks to ban military-style weapons.

If Slide Fire's claims are taken at face value, the rate of fire possible with a slide stock is roughly comparable to that of a fully automatic M16 military assault rifle. Real machine guns cost many thousands and require an expensive, hard-to-get federal permit that makes them, if not entirely illegal, largely unavailable to most civilians. But about $350 and a few minutes' installation time will give you what many fans of slide or "bump" stocks call a "legal full-auto."

"Since the 1994 Assault Weapons Ban expired, we have seen a rapid rate of technological improvements in assault weapons, and that concerns me," Feinstein, a California Democrat, said in an email response to questions from The Associated Press.

"This replacement shoulder stock turns a semi-automatic rifle into a weapon that can fire at a rate of 400 to 800 rounds per minute," she said. Noting the strong existing federal regulation of machine guns, she added, "I strongly believe that devices allowing shooters to fire at similar rates should also be outlawed."

The marketing of devices like slide stocks directly counters Feinstein's call for restrictions, reflecting a tense debate over how much gun is too much gun — or whether there is such a thing. It's a debate where perceptions count.

The federal government first restricted the possession of automatic weapons in 1934, in the wake of such gangland shootings as Chicago's infamous St. Valentine's Day Massacre. In 1986, the National Firearms Act was amended to prohibit the transfer or possession of machine guns by civilians, with an exception for those lawfully possessed before the law's effective date.

In a true automatic, one trigger pull can unleash continuous fire until the magazine is empty. The force of each discharge pushes back the gun's bolt and ejects the spent bullet casing. A semi-automatic weapon requires one trigger pull for each round fired.

Numerous attempts to design retrofits have failed — both mechanically and legally. Then someone finally cracked the code.

A bump stock fits over a rifle's "buffer tube," replacing the gun's shoulder rest. A "support step" attached to the pistol grip partially covers the trigger opening, preventing contact with the finger. By holding the pistol grip with one hand and pushing forward on the barrel with the other, the finger comes in contact with the trigger. The recoil causes the gun to buck back and forth, "bumping" the trigger.

So, technically, the finger is "pulling" the trigger for each round fired.

Several companies offer a version of this technology. Slide Fire Solutions of Moran, Texas, near Abilene, is the leader.

Founder and president Jeremiah Cottle, a retired Air Force staff sergeant, did not respond to repeated requests for comment. But according to the company's website, Slide Fire's stock design is based on "principles that have been used for over 40 years to bump fire."