BUNNLEVEL, N.C. (AP) -- 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."
"But unlike traditional bump firing, the Slidestock allows the shooter to properly hold the firearm and maintain complete control at all times," the site reads.
Each plastic Slide Fire stock -- available for AR- and AK-style rifles -- comes with a copy of a 2010 letter signed by John R. Spencer, firearms technology chief for the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, deeming it an unregulated firearm part.
In seeking ATF's blessing, according to Spencer's letter, Slide Fire claimed the device was "intended to assist persons whose hands have limited mobility." But gun shop owners have told the AP that most of their sales have been to able-bodied shooters.
Dorothy Royal, manager of Surf City Guns in southeast North Carolina, sells about a dozen Slide Fire stocks a month, mostly for AR-type rifles. Although many of her customers are wounded veterans, she guesses about 70 percent of the buyers have no disability.
"To the best of my knowledge, without taking them outside and putting them through a physical test," she said.
Royal can see how a lay person might have difficulty telling one of these weapons apart from a real machine gun. But she said there are differences.
"If these were designed to work with a belt-fed gun, you would have a totally different character here," she said. "You go through a lot of ammo here. It's not accurate."
She clearly hadn't seen the video posted on Slide Fire's website.
Produced by the shooter magazine Guns&Ammo, the video features Sgt. Jason Teague, a sniper with an Atlanta-area police SWAT unit. The video caption says the marriage of Valkyrie Arms' belt-fed drum magazine and the Slide Fire stock produces an offspring that "bridges the firepower gap between a rifle and a machine gun."
With a combination of short and long bursts, Teague perforates the face and chest of a cleaver-wielding assailant on a target with a fusillade of red- and green-tipped "Zombie Max" bullets.
"This is definitely something that's a game-changer for you guys out there who want to put down a heavy volume of fire," he says. "A lot of firepower -- EASILY able to fight off that next big horde that comes after you."
And, Teague assures, "it's completely legal."
Cottle's home page boasts that "Slide Fire's patented technology allows the shooter to accurately and safely fire your rifle as quickly as you desire."
Some full-auto purists agree.
According to his YouTube channel, Jeffrey Zimba has spent more than two decades "in the Military Firearms industry." Over the years, he's tested many devices and gadgets intended to simulate the rush of firing a machine gun, but hadn't found "anything that really gave you something that you would think was close to a full auto.
"Not," he said, "until now."
In a video, Zimba unloads two clips from two different rifles into a pair of paper targets from 15 yards. All but one of the rounds is in the black.
"Proof's in the pudding to me," he says. "As far as I'm concerned, very controllable. Not a waste of ammo."
Shooting instructor Frankie McRae disagrees.
"To get consistent" requires unconventional training, says McRae, co-owner of Range 37, a shooting club in Bunnlevel, not far from the Army's Fort Bragg. "You're not holding the gun correctly. The gun has to move within the stock here, and that takes away from the fundamentals of a good stance and good grip with the rifle."
Bump-fire weapons don't appear to have turned up at crime scenes and aren't generally on the law enforcement radar. McRae says banning the devices wouldn't affect criminals, who would continue to buy restricted weapons illegally from "other criminals."
"I wouldn't want one of these if I was going out to hunt people," McRae says after emptying a couple of magazines from a fully automatic Colt CM901.
On its "frequently asked questions" page, Cottle's company notes that the technology has stood the test of time.
"By definition, the SSAR-15 and our other products are not adjustable stocks or trigger manipulation devices," the site says. "Slide Fire has not been notified by any individual state that our products conflict with any state laws."
California and New York officials do see a conflict.
"New York has long had a prohibition on machine guns and any weapons capable of automatic, or rapid fire," Rich Azzopardi, a spokesman for New York Gov. Andrew Cuomo, told the AP. "This clearly includes firearms modified with one of these devices."
Michelle Gregory, spokeswoman for the California Department of Justice, says bump stocks would be considered illegal "multi-burst trigger activators" under state law -- although that interpretation has yet to be tested in court.
And as Florida inventor William Akins can attest, a letter from the ATF is no guarantee.
In 2000, Akins was granted a patent for a "Method and Apparatus for Accelerating the Cyclic Firing Rate of a Semi-Automatic Firearm." The "Akins Accelerator" included a spring-loaded stock that, when decompressed, shoved the receiver forward again.
ATF wrote two letters approving the device, but later rescinded them. Akins challenged the decision in court, but lost, and legal expenses and business losses forced him to abandon the venture. But he designed a new type of bump stock without a spring, and licensed it to Indiana-based FosTecH Outdoors, LLC, whose aluminum "DefendAR-15" and "Bumpski" stocks "simulate the discharge of automatic firearms."
That company is currently suing Cottle's in federal court for patent infringement. Akins backs that contention, but is equally concerned with what he sees as Feinstein's attempted infringement on the constitutional right to bear arms.
"They quite literally make it up as they go along," he says of the senator and ATF. "Why is it that if it fires faster, suddenly that changes the intent of someone who owns it from being a legal, law-abiding citizen to someone that has a killing machine that they're going to use?"
Slide Fire Solutions: http://www.slidefire.com/
Breed reported from Bunnlevel, and Geller from New York. Associated Press writer Don Thompson also contributed from Sacramento, Calif. Follow Breed on Twitter at http://twitter.com/(hash)!/AllenGBreed