As details continue to emerge about Sunday night's mass shooting in Las Vegas, a national spotlight has focused partially on a legal firearm accessory used by the shooter that gun control advocates say might have worsened the carnage he wreaked.
Authorities have confirmed 23 firearms were found in the Mandalay Bay hotel room Stephen Paddock used as a sniper's nest to fire on thousands of people below, noting that more than half of those weapons were equipped with "bump stocks."
While the possession of machine guns was severely restricted by an amendment to the National Firearms Act in 1986, the attachment allows experienced shooters to fire semi-automatic weapons, guns that fire one bullet per trigger pull, at a rate much closer to that of an automatic weapon.
Slide Fire Systems, one of the leading manufacturers of bump stocks, sells versions of the component for less than $200 online and lauds their capacity to increase a shooter's fire rate.
"Bump firing is a well-established capability that uses the recoil of a semi-automatic firearm to fire multiple shots in rapid succession. The patented Slide Fire® rifle stock allows shooters to safely and accurately bump fire their rifles without compromising safety and accuracy," the website reads.
The attachment, a replacement for standard stocks, harnesses the firearm's recoil and allows shooters to pull the trigger more quickly than they could naturally.
By resting the trigger finger on a support step, holding a back grip with one hand and pushing forward on the barrel with the other hand, the shooter's finger pulls the trigger. The recoil then causes the gun to buck back and forth, repeatedly "bumping" the trigger against the finger.
Because the gun is still technically a semi-automatic firing only one round per trigger pull, weapons equipped with the attachment are still legal, according to Michael Knight, special agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives.
"Traditionally, the item is not classified as a machine gun. It is an accessory to the firearm," he said Wednesday afternoon. "All they do is make your finger move more rapidly than you could do it on your own."
"It does fire more rounds in a shorter period of time, but by law it doesn't meet the definition of an automatic firearm."
Testimonies posted online by consumers demonstrate as much — several people have written reviews of a Slide Fire AK-47 stock being sold online by Cabela's, an outdoors outfitter that has a store in Chattanooga.
On Tuesday, the stock was advertised as an "innovative AK-47 stock which uses bump-fire technology to shoot as quickly as desired." The site also noted it is approved by ATF and requires no special permits. But by Wednesday, it had been removed from the online store.
"It took a few times to get used to slide fire, and other than that, this equipment was rocking so hard it had a screw come off," wrote one person with the username "fullautojam."
"I really never had so much fun at my friend's berm! This is truly an advance to even more fun shooting. I swear it was 600 to 700 rounds per minute or faster! (Poor gallon bottles flying 30 feet in the air colored water everywhere!) Love at first pull!"
The stocks have been available since 2010 when the government deemed they did not violate federal law, but Chattanooga gun store owners acknowledge the component can help simulate the fire of an automatic weapon and there's business to be done in the industry.
"Really the bump stock is probably the closest thing to emulate a fully auto weapon," said David Smith of Dave's Shooting Supply. "That's a market that's got a lot of money in it."
John Martin, owner of Shooter's Depot, has bought and sold automatic firearms and believes there should be more guidelines with regard to the sale and use of bump stocks.
"I am not a proponent of bump fire," he said. "They've deemed it a non-firearm item, but anything that you put in a firearm that allows it to fire automatically should be regulated."
However, he pointed out that simply owning a bump stock doesn't mean a shooter can use it effectively.
"Nobody picks up three balls and automatically starts juggling. That is a learned skill," he said. "That guy didn't just buy that stock and go up in that building and start shooting it. You have to take it to the range and practice with it to fire it efficiently."
The stock has come under increased scrutiny in the wake of the attack and revelations that Paddock had several attached to his firearms, prompting legislators to begin weighing options. A bill introduced Wednesday by Sen. Diane Feinstein, D-Calif., targets the accessory specifically.
"It shall be unlawful for any person to import, sell, manufacture, transfer, or possess, in or affecting interstate or foreign commerce, a trigger crank, a bump-fire device, or any part, combination of parts, component, device, attachment, or accessory that is designed or functions to accelerate the rate of fire of a semi-automatic rifle but not convert the semi-automatic rifle into a machinegun," the bill states.
But the suggestion of prohibition could also cause an uptick in the sale of bump stocks and other accessories being discussed.
Martin said business booms in the wake of heavily publicized shootings, especially when legislators move to tighten gun control. His sales kicked into overdrive when then-President Barack Obama's administration began focusing on restricting access to firearms.
"The country just went crazy. Anybody that grew up in a gun culture, whether they were a gun nut or not, became panic-stricken," he said.
"You thought they're going to take them out of production and there's never going to be another one. It didn't take the industry very long to be out of product. Panic-buying set in."
As far as ATF is concerned, the accessory will remain legal until legislators decide it should be otherwise, Knight said.
"We don't create the laws, we enforce them," he said. "If the Congress passes any particular laws, then we would enforce those laws to include possibly changing classifications."
Whether the law is changed or not, the agency already has its hands full with a string of shootings and other situations involving firearms that shows no sign of relenting anytime soon.
He said ATF has dealt with the Las Vegas shooting, a church shooting in Nashville that claimed a woman's life, and the arrest of a man in Washington County, Tenn., who was found driving with multiple unlicensed firearms authorities said he had modified to be automatic. All three incidents occurred within the last week.
Knight said the public's safety is the agency's highest priority, but residents should report anything they think is suspicious to law enforcement immediately. Then, perhaps, flags can be raised on people such as Paddock who had no criminal history.
"If the criminal element is not on any law enforcement's radar screen, if they've never had any criminal history, if they've never had any interaction with law enforcement, how would law enforcement know that something is going to take place? That's where the public comes in," he said.
"It's going to take everybody to resolve this. Law enforcement cannot resolve this issue alone."
The Associated Press contributed to this story.
Contact staff writer Emmett Gienapp at firstname.lastname@example.org or 423-757-6731. Follow him on Twitter @emmettgienapp.