Many people are wondering how the Las Vegas gunman fired so many rounds so quickly, killing 59 people and injuring more than 500 others.
Police recovered 23 guns inside his hotel room and over half of them had an accessory that could alter its rate of fire.
"There were 12 bump fire stocks identified on the firearms in the hotel room," ATF Agent-in-Charge Jill Snyder said.
"A bump fire stock allows you to simulate automatic fire," Caleb Giddings said.
Giddings, general manager of National Armory in Pompano Beach, has worked in the firearms industry for decades.
"It is largely viewed in the professional firearms community as a gimmick and kind of a cheap toy for turning money into smoke and noise," he said.
Giddings said bump stocks are legal because they do not alter the mechanics inside the gun, but the mechanics of how the gun is fired.
"A bump fire stock uses the recoil of the weapon," he said.
The modified sliding stock and pistol grip trapping the trigger, harness the recoil to help the shooter fire faster.
Giddings is also a licensed automatic weapons dealer.
He said with an AK-47 machine gun, he can fire 500 rounds in a minute.
Giddings said a skilled bump stock shooter could match that rate of fire.
"I wouldn't want to come across one on the street somewhere. Let's put it that way," Damon Benedict, who has fired a bump stock rifle before, said. "I couldn't believe that it actually worked and that it was legal."
"They were an extremely popular retail item from about 2012 to 2014, and then the interest in them sort of died off," Giddings said. "So they haven't really been moving, so we didn't bother to restock."
Giddings said in 2017 there has been high interest in the product.
"I have gotten multiple calls from people interested in purchasing them," he said.