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'Bump Stocks' Now at Center of US Gun Debate, But What Are They?

FILE - A little-known device called a "bump stock" is attached to a semi-automatic rifle at the Gun Vault store and shooting range, in South Jordan, Utah, Oct. 4, 2017. The device was used by Las Vegas shooter Stephen Paddock.

The recent mass shooting in Las Vegas, Nevada, has some Republican lawmakers considering gun control legislation, a dramatic shift from what has historically been their party's general aversion to gun regulations of any kind.

The catalyst behind the change is a firearm accessory called a "bump-fire stock," more commonly known as a bump stock. The device, which significantly increases the firing rate of semi-automatic rifles, was used by shooter Stephen Paddock as he killed 58 people and wounded hundreds of others.

How bump stocks work

Bump stocks were initially intended to assist people with restricted hand mobility fire a semi-automatic weapon without pulling the trigger each time a bullet is fired. They can be installed over the weapon's rear shoulder-stock assembly, which is the part held against the shoulder. With applied pressure, the weapon fires continuously, increasing the firing rate to nearly that of a machine gun.

Legislation introduced this week by Democratic Senator Dianne Feinstein to ban the accessory estimates bump stocks can boost the firing rate from between 45 and 60 rounds per minute to between 400 and 800 rounds per minute.

History of bump stocks

The federal government approved the sale of bump stocks in 2010 after determining they did not violate federal law.

The leading seller of bump stocks, the Texas-based company Slide Fire, petitioned the Bureau of Alcohol, Tobacco, Firearms and Explosives in 2010 to approve the device as a way to help people with disabilities replicate an automatic weapon. In its approval letter, which is posted on Slide Fire's website, the ATF wrote "the 'bump stock' is a firearm part and is not regulated as a firearm."

Legal under current law

At a news conference in Las Vegas on Tuesday, ATF special-agent-in-charge Jill Snyder said, "Bump-fire stocks, while simulating automatic fire, do not actually alter the firearm to fire automatically, making them legal under current federal law."

The National Rifle Association, which has lobbied against gun control proposals, has not commented on the massacre or Feinstein's legislation.

President Donald Trump has also remained mum on gun control measures. While visiting victims Wednesday at a Las Vegas hospital, Trump was asked by a reporter if the U.S. has a "gun violence problem," Trump responded, "We won't talk about that."