A proposal to ban devices that modify semiautomatic guns to fire like fully automatic firearms is gaining traction in Congress, with some Republican lawmakers signaling openness to legislation the bill's supporters say would reduce the likelihood of massacres like the one that took place in Las Vegas last week.

On Thursday, House Speaker Paul Ryan told MSNBC that the House would be willing to consider taking a look at a ban of "bump-stock" accessories that can be used to make semiautomatic weapons capable of firing hundreds of rounds per minute.

"Fully automatic weapons have been banned for a long time," the Wisconsin Republican said. "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."

Since the December 2012 Sandy Hook massacre, the gun violence debate in Washington has been caught in a now-familiar cycle: a call for restrictions on access to firearms, followed by politicians saying the wake of a tragedy is not the time to discuss politics and then opposition to any infringement on Second Amendment rights. Bills to change laws – close background check loopholes, reintroduce a ban on assault weapons – are floated and voted down, or more often, never see a vote at all.

A similar cycle appeared to be underway following Sunday's shootings in Las Vegas. But the scale of the destruction – with at least 58 dead and 500 wounded, the incident set a new high water mark for the deadliest mass shooting in modern U.S. history – and the shooter's use of the bump-stock device, seems to have opened a narrow avenue for bipartisanship.

The apparent bipartisan momentum around an issue of gun control is exceedingly rare – and could still be easily tripped up over disagreements about the scope and details of a ban.

In addition to California Sen. Dianne Feinstein's legislation, which has 29 cosponsors, 140 House Democrats led by Rep. David Cicilline of Rhode Island introduced a companion bill in the lower chamber. A spokeswoman for Rep. Carlos Curbelo said the Florida Republican plans to introduce a bump stock ban of his own in the coming days.

Before Sunday's shooting, bump-stock devices were relatively obscure. Law enforcement officials said the Las Vegas gunman had outfitted 12 firearms with the devices, allowing him to spray thousands of rounds onto a crowd of 22,000 at a music festival Sunday night.

While automatic firearms are strictly regulated and require special licenses to own, "bump stocks" are seen as a workaround and can be purchased for about $200. The device uses the gun's recoil to "bump" the trigger against the shooter's finger in rapid succession; the gun still technically qualifies as semi-automatic under the legal definition that requires the trigger be pulled for each round fired.

Feinstein's bill would ban the sale of such devices.

"I know what guns can do," Feinstein, the author of the now-expired assault weapons ban of 1994, said in introducing the bill. "This is taking it into war."

On Wednesday, the proposal seemed to gain steam, with a number of Republicans expressing support of at least discussing such a ban.

"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, the No. 2 Republican in the Senate. "It seems like it's an obvious area we ought to explore and see if it's something Congress needs to act on."

He found company with Sen. Ron Johnson, R-Wis., chairman of the Senate Homeland Security Committee, who on Wednesday told reporters he would "have no problem banning those."

"To me that's already illegal," he said of unregulated sales of machine guns. "So you shouldn't have anything that facilitates that so easily."

Sen. Lindsey Graham, R-S.C., said a bump stock ban is "something I'd be interested in looking at to see if you a law change would matter… I'd be willing to look at that."

Texas Rep. BIll Flores told The Hill he believes bump stocks "should be banned."

"There's no reason for a typical gun owner to own anything that converts a semiautomatic to something that behaves like an automatic," he said.

Democrats on Thursday sought to encourage their Republican colleagues.

"We take an oath to protect and defend the American people," House Minority Leader Nancy Pelosi, D-Calif., told reporters. "We're not protecting them by not having the gun laws that are suitable."

"Hopefully we can bring that to the floor and ban something that enables a shooter to spread murderous fire on innocent people," she said.

And Senate Minority Leader Chuck Schumer, D-N.Y., called on President Donald Trump to come out in support of the measure.

"President Trump, are you going to wait to hear what the NRA says first? Are you going to wait for the NRA to give you the green light?" Schumer said Thursday on the Senate floor. "You ran your campaign saying you were beholden to no one. You fashion yourself as a s strong man, well, are you going to show that now?

"You know what the right thing to do is," he said.

But even as the proposal gains momentum, lawmakers who oppose gun control measures were adamant that they would not support the measure.

"I don't think we ought to punish 80 to 90 million gun owners who have a right to own a weapon under the Constitution because of the act of one idiot," Sen. John Kennedy, R-La., said Wednesday. "Just like I don't think we ought to condemn all Muslims because of the act of one jihadist."

And Rep. Steve Scalise of Louisiana, the House majority whip who returned to Congress this week after surviving a shooting in July, said he opposed new gun control measures.

"I think it's a shame that the day somebody hears about a shooting, the first thing they think about is, how can I go promote my gun-control agenda, as opposed to saying, how do I go pray and help the families that are suffering?" he told The Washington Post Wednesday.

On Tuesday, Senate Majority Leader Mitch McConnell, R-Ky., declined to answer reporters' questions about whether he would be amenable to bringing the measure up in the Senate, telling reporters that it's "completely inappropriate to politicize an event like this."

But on Thursday, the National Rifle Association -- which bans bump stocks at their own firing range -- weighed in on the debate.