Las Vegas gunman used a ‘bump stock.’ So what is it and how does it work?

That sound. That terrible sound.

We now know more about that distinct rapid-fire sound from Sunday’s shooting in Las Vegas that ended with 59 people dead and more than 500 wounded. It appears to have come from a rifle outfitted with a modification device called a “bump stock,” authorities told the Associated Press.

At least 12 “bump stocks” were found along with 47 guns, including rifles, at three locations, including the hotel room on the 32nd floor of the Mandalay Bay Resort where 64-year-old Stephen Paddock opened fire on a crowd of at least 22,000 people attending an open-air country music concert.

Authorities have not shared any motive for the killings, but the presence of high-power rifles in the execution of the deadliest mass shooting in modern U.S. history has predictably renewed the debate over gun legislation.

A part of that debate is now focused on what the AP called a little-known device, the “bump stock.” Here are some answers about “bump fire” and the device that can make a rifle spray hundreds of bullets per minute.

What is a ‘bump stock’ and how does it work?

A semi-automatic weapon allows a shooter to fire only one round per trigger squeeze. A “bump stock” is a device that attaches to a semi-automatic rifle, replacing the original butt of the weapon. The device assists the shooter by making the finger “bump” against the trigger.

Here’s a video that illustrates how it is installed and used.

Are they legal?

Yes. Technically a “bump stock” does not modify a rifle to make it automatic, which is illegal. Instead, the device only assists the shooter’s finger on the trigger.

In a letter the Bureau of Alcohol, Tobacco, Firearms and Explosives sent to Slide Fire, one of the biggest “bump stock” manufacturers in America, the agency clearly defines the device as legal in these terms:

“The stock has no automatically functioning mechanical parts or springs and performs no automatic mechanical function when installed … Accordingly, we find that the ‘bump-stock’ is a firearm part and is not regulated as a firearm under Gun Control Act or the National Firearms Act.”

How long have ‘bump stocks’ been around?

The stocks have been around for less than a decade, the AP reported. It wrote that the government “gave its seal of approval to selling them in 2010 after concluding that they did not violate federal law.”

How many have been sold?

The Associated Press reports that it’s unclear.

What does the gun industry say about them?

Per that same AP report:

Erich Pratt, executive director of Gun Owners of America, said the industry is prepared to have the devices scrutinized by lawmakers and gun-control advocates. That happens regularly after a major shooting. But he and others defended their use, suggesting it’s unfair to go after firearms when other weapons — trucks and fertilizer, for example — aren’t as quickly criticized after deadly attacks.

“Ultimately, when Congress ... looks at this, they’ll start asking questions about why anybody needs this, and I think the answer is we have a Bill of Rights and not a Bill of Needs,” Pratt said

What do the country’s politicians say?

The New York Times reports that senior California Sen. Dianne Feinstein proposed outlawing bump stocks in 2013 “but Congress has not acted on her proposal.”

The Times reported that Feinstein proposed a ban again on Tuesday.

Have some thoughts to share?

Join me in a conversation: Shoot me a private email with your thoughts or ideas on a different approach to this story. As always, you can also send us a tweet. 

Email: luis.gomez@sduniontribune.com

Twitter: @RunGomez

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