A bump fire stock that attaches to an semi-automatic assault rifle to increase the firing rate is seen at Good Guys Gun Shop in Orem, Utah, U.S., October 4, 2017.

Top Republican lawmakers are signaling they will examine whether to regulate the device used by the Las Vegas gunman to boost his firing frequency.

House Speaker Paul Ryan says Congress should "look into" the so-called bump stock tool, which can make semi-automatic rifles fire more rapidly. Sen. John Cornyn — the No. 2 Republican in the Senate — on Thursday said "it's worth our serious consideration" to ban bump stocks.

They are part of a growing chorus of Republican lawmakers who want to at least critically examine — or outright ban — the device used in the deadliest mass shooting in modern American history.

"I didn't even know what they were until this week, and I'm an avid sportsman," Ryan said in comments that aired Thursday on MSNBC. "So I think we're quickly coming up to speed with what this is. Fully automatic weapons have been banned for a long time. Apparently this allows you to take a semiautomatic and turn it into a fully automatic. So clearly that's something we need to look into."

The powerful National Rifle Association on Thursday backed additional regulations on the devices.

Audio of the attack on the Route 91 Harvest musical festival in Las Vegas contained rapid fire bursts into the crowd. Fifty-eight people were killed and hundreds were shot or injured in the stampede to escape.



Investigators said the gunman, Stephen Paddock, had 12 rifles equipped with bump stocks.

With the devices, semiautomatic rifles can fire hundreds of rounds a minute.

Sen. Dianne Feinstein, D-Calif., introduced legislation on Wednesday to ban bump stocks. Some Republicans support banning the devices, while others said they were open to hearings on bump stocks.

The comments from Ryan and other top Republican lawmakers are significant because efforts to pass new gun control measures following massacres in Orlando, Florida, Newtown, Connecticut, and elsewhere failed in Congress. Any effort to ban bump stocks could still face a tough test in a Congress controlled by Republicans, who typically avoid efforts to tighten gun laws.

Rep. Adam Kinzinger, R-Ill., on Thursday called on the Bureau of Alcohol, Tobacco, Firearms and Explosives to re-evaluate its rules on bump stocks. He said the ATF determined the tools complied with federal law in 2010 and 2012.

"The ATF must re-evaluate these devices, and it is my hope that they conclude these mechanisms violate the spirit, if not the letter, of the law," Kinzinger said in a statement. "In the meantime, my colleagues and I will consider legislative options, because these fully-automatic simulator devices have no place in civil society."

Cornyn, the Texas Republican, previously told reporters that he asked Sen. Chuck Grassley, R-Iowa, to hold a Judiciary Committee hearing on bump stocks.

The No. 3 Republican in the Senate, Sen. John Thune of South Dakota, also said bump stocks are "something we ought to look into," according to Politico.