WASHINGTON (Reuters) - A backlash against “bump stock” gun accessories, which enable rifles to be turned into rapid-fire guns, grew in the U.S. Congress on Thursday as House Speaker Paul Ryan opened the door to possible debate on controlling the devices.     “Clearly that’s something we need to look into,” Ryan told radio talk show host Hugh Hewitt, referring to the accessories. He added that many lawmakers in the Republican-controlled Congress had not been aware until now that such devices existed. An excerpt from the interview aired on MSNBC. The National Rifle Association, a powerful opponent of most gun control initiatives, so far has been silent on whether it would support or oppose efforts in Congress to ban or control bump stocks.  A shooting rampage on Sunday night in Las Vegas that killed 58 people and wounded nearly 500, the most deadly mass shooting in modern U.S. history, has reignited debate around regulation of firearms. Officials said 12 of the rifles authorities recovered from a hotel suite in Las Vegas used by gunman Stephen Paddock were fitted with bump stocks, allowing the guns to fire almost as though they were automatic weapons.  “I didn’t even know what they were until this week,” Ryan said, referring to bump stocks. “I think we’re quickly coming up to speed with what this is.” Ryan and other leading Republicans have not embraced specific legislation, however.  The House speaker’s remarks followed a call on Wednesday by the U.S. Senate’s No. 2 Republican, John Cornyn, for lawmakers to investigate bump stocks, as Democrats pushed for a ban on the devices. On Thursday, Republican House Judiciary Committee Chairman Bob Goodlatte also said the matter should be looked into. House Democratic leader Nancy Pelosi said at a weekly press conference that Congress should promptly pass legislation toughening background checks on gun buyers. She also touted Democratic legislation stopping bump stocks. “Hopefully we can bring that to the floor and at least pass a bill that bans, something that enables a shooter to spray murderous automatic fire on innocent people,” Pelosi said. Republican Representative Carlos Curbelo was preparing his own measure to ban the ownership, manufacture and transport of the devices. While he said there was growing bipartisan consensus, he cautioned against assuming that a legislative win was certain.  “Let’s not get ahead of ourselves. We hope that there will be a breakthrough,” Curbelo told reporters, adding, “But I think this is just such a blatant exploitation of the law, a circumvention of the law.” Indeed, Republican Senator Dean Heller, who could face a tough re-election fight next year, told Fox News, “We’re going to have this conversation, but let me be clear, I’m not interested in watering down the Second Amendment.” Republicans, and some Democrats, are generally reluctant to push for tighter controls on firearms ownership, which is protected by the Second Amendment of the U.S. Constitution.  Automatic weapons have been largely illegal for decades,  but bump stock devices offer a way around that. Democratic Senator Dianne Feinstein has called for bump stocks to be banned.  Representative David Cicilline, also a Democrat, has proposed a ban too, with a House bill that he said has 148 co-sponsors. None are Republicans, he told CNN, although he is talking with about five or six conservatives to seek their support.  In the interview with Ryan aired by MSNBC, the top House Republican gave no other details about what action the Republican-controlled House might take toward bump stock devices, or what the timeline would be for any legislative steps. Republicans also control the Senate and the White House. 