Bumps stocks are a gun accessory that modify semi-automatic rifles to shoot faster, mimicking banned fully automatic rifles. Las Vegas shooter, Stephen Paddock, installed them on several rifles found in his hotel room after the mass shooting last week that left at least 59 dead and over 500 injured, according to authorities. Now, the device is being bought up.

A semi-automatic weapon shoots one bullet per trigger pull and are legal in the U.S. Fully automatic weapons or machine guns fire more than one bullet per trigger pull and are mostly illegal in the U.S. Civilians can’t own automatic weapons manufactured after 1986, and weapons built before then are expensive and more regulated than other guns. Those owners are also put into a federal database.

A bump stock is a device that  modifies the stock, or part that pushes against your shoulder, in a rifle and uses the force of the recoil of a shot to “pull the trigger.” The recoil moves the weapon much faster than a finger allowing the gun to shoot bullets faster. The device is not banned because it doesn’t mechanically alter a weapon, which is illegal. Some states, like New York, New Jersey and California have additional gun regulations to federal statutes that effectively “ban” modifiers like the bump stock.

Some stores where the item is sold are being bought up and a major manufacturer, Slide Fire, has sold out of the item.

“Anybody that wants to get them is probably just worried that they're going to be banned,” said Kellie Weeks who owns a gun store in Georgia to the Australian Broadcasting Corporation.

Several online retailers are listing the device as out of stock, and major retailers like Walmart and Cabela’s have pulled them off their websites.

The device, originally intended to help people with disabilities shoot, has been thrust into the spotlight. Some gun stores contacted by International Business Times in states like Massachusetts said they have never stocked or sold the device.

Some Republican lawmakers, typically opposed to gun control legislation, are considering banning the device in the wake of the shooting.

“I own a lot of guns, and as a hunter and sportsman, I think that’s our right as Americans, but I don’t understand the use of this bump stock,” said Sen. John Cornyn of Texas, to the New York Times Wednesday. “It seems like it’s an obvious area we ought to explore and see if it’s something Congress needs to act on.”

Rep. Bill Flores, a Texas Republican told The Hill, the device should be outlawed.

“I think they should be banned,” said Flores. “There’s no reason for a typical gun owner to own anything that converts a semiautomatic to something that behaves like an automatic.”