Las Vegas shooting: What is a bump stock device?

HOUSTON (FOX 26) - Videos of shooters using bump fire stock are all over Youtube. They are thrilling or horrifying, depending on your point of view. But regardless of how you feel about them, they are legal.

The Bureau of Alcohol Tobacco Firearms and Explosives regulates devices like this. Its panel of gun and legal experts determined they broke no existing laws. That was back in 2010, says one former agent.

"What's interesting is when you read the approval letter the company that asked for the ruling on this had suggested that the primary purpose of the bump stock was to assist those shooters who had a disability and could not use their hands to fire a traditional assault weapon,” says David Chipman with Americans for Responsible Solutions, a gun violence prevention organization.

As far as anybody knows the Las Vegas killer had no such disabilities, but he did have the money to buy at least one, possibly more for his AR 15 rifles. Those are the rifles it appears he used to shoot so many people.

They work by replacing the shoulder stock with a spring loaded version that uses the gun's own recoil to slam the trigger into the shooter's trigger finger. Experts say they are not as effective and reliable as an a machine gun, but they do have other advantages.

"If this was a registered receiver, M-1616, you are looking at $15,000 and up. Whereas this is about $150 and you don't have to go through a background check and no waiting period,"  says Steven Ou, owner of the Arms Warehouse in the Austin area.

He says they don't sell them but found one for sale for just shy of $300 in a sporting goods store in the Houston area. So will the BATF change it's ruling about these stocks? Probably not, says Chipman.

"I think government agencies are concerned about revisiting decisions. But in this case it clearly had some unintended consequence," says Chipman.

Online sales of the devices are now surging.