The deadliest mass shooting in modern American history has stalled a Republican proposal that would make it easier to buy gun suppressors.

The bill's author, Rep. Jeff Duncan (R-S.C.), had said a vote on the Hearing Protection Act, wrapped into the broader Sportsmen's Heritage and Recreational Enhancement (SHARE) Act, would happen soon.

But that timeline changed after a gunman opened fire on a concert from a hotel window in Las Vegas last Sunday night, killing dozens of people and injuring hundreds more.

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Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.) told reporters on Tuesday that he doesn't know when the legislation will be scheduled for a floor vote.

It’s the second time the bill has been delayed by a mass shooting.

The day the House Natural Resources subcommittee was expected to hold a hearing on the bill in June, a gunman opened fire on Republican lawmakers who were practicing for a charity baseball game in Alexandria, Va.

The bill eventually made it before the full committee for a hearing on Sept. 12. It advanced the following day by a vote of 22-13.

Here are five things to know about the bill.

It makes buying a suppressor easier

The legislation removes suppressors from the purview of the National Firearms Act (NFA) and allows a buyer to undergo an instant background check at a gun store through the National Instant Criminal Background Check System.

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The legislation also does away with the $200 transfer tax fee that’s now required on top of the price of the suppressor.

The broader sporting bill the Hearing Protection Act has been attached to expands access to hunting on federal lands, allows for the lawful import of any firearm or ammunition not already regulated by the NFA and prevents the government from reclassifying popular bullets used in hunting rifles as “armor-piercing” ammunition.

Buying a suppressor now takes months

After selecting a suppressor, a buyer has to fill out an application and registration form, known as a Form 4, at a gun store.

In addition to the form, which asks for your name, address and Social Security number, buyers have to provide two FBI fingerprint forms, a passport style photo and their $200 transfer tax. Two copies of the form are submitted to the Bureau of Alcohol, Tobacco, Firearms & Explosives (ATF) and a third is sent to the local chief law enforcement officer to notify them that you've purchased an NFA item.

Most shops also ask for an up-front payment for the suppressor, which can run anywhere from a few hundred dollars to over $1,000, depending on the quality and type of gun it’s for.

Robert Marcus, co-owner of Bob’s Gun Shop in Norfolk, Va., said that under the Obama administration it was taking anywhere from four months to a year for the ATF to approve an application.

“At four months we were selling about 150 a year,” he said. “At 12 months, it’s less. I’d say it’s been cut by almost a third.”

A suppressor can only muffle a gun’s sound

Knox Williams, president and executive director of the American Suppressor Association (ASA), describes a suppressor as a muffler for a firearm.

“The exact same science behind a car muffler is at work,” he said. “It’s allowing the hot gases being expelled to slowly cool in a more controlled environment.”

Think of the sound an inflated balloon makes when it’s popped with a needle, Williams said. Now take the same balloon, untie the end a little and pop it with the same needle.

Williams said a suppressor reduces the sound of a gun by 20 to 35 decibels, on average, depending on the type of gun. It doesn’t silence the gun. That, he said, is “physically impossible.”

The bill is controversial

Gun control advocates claim the gun lobby is pushing the legislation to increase the sales of suppressors and say their widespread use will ultimately lead to deadlier mass shootings.

Though the legislation requires buyers to pass an instant FBI background check, Andrew Zucker, a spokesman for Everytown for Gun Safety, said that step can be avoided if a suppressor is purchased online from an unlicensed seller or at a gun show.

“When silencers fall into the wrong hands, they can have incredibly dangerous consequences,” he said.

“Distorting the sound of a gun makes it more difficult for people near a gun to respond and also law enforcement and civilians to know where gun shots are coming from. It puts people’s safety at risk.”

On Twitter this week, Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE said the shooting in Las Vegas would have been worse had the gunman used a suppressor.

"The crowd fled at the sound of gunshots. Imagine the deaths if the shooter had a silencer, which the NRA wants to make easier to get," she tweeted, referring to the National Rifle Association.

The NRA declined to speak to The Hill about the events in Las Vegas or the fate of the bill. James Ouimet, NRA’s director of federal affairs, was originally scheduled to testify in support of the legislation at the June hearing that was postponed. When the hearing was later held on Sept. 12, Ouimet was no longer among the witnesses.

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In addition to the support of the NRA, the bill has the backing of the ASA. In a blog post at the end of 2016, the association credited its outgoing general counsel Michael Williams as the “lead author" of the text of the bill.

Williams told The Hill on Wednesday that it's disingenuous for people to say suppressors will lead to deadlier mass shootings.

“I can understand why they would think that would be the case, but that’s simply not true,” he said. “Anyone around a suppressor understands they are not quiet, especially semi-automatic rifles that use them are still incredibly loud.”

There’s no guarantee it can pass Congress

The standalone bill gained the support of 161 Republicans and four Democratic co-sponsors, including Reps. Gene Green Raymond (Gene) Eugene GreenTexas New Members 2019 Two Democrats become first Texas Latinas to serve in Congress Latina Leaders to Watch 2018 MORE (Texas), Henry Cuellar (Texas), Colin Peterson (Minn.) and Peter DeFazio (Ore.).

But DeFazio, who sponsored the bill in June, withdrew his support on Wednesday.

In a statement to The Hill, DeFazio said he withdrew his support for the bill in light of the "horrific events" in Las Vegas.

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"I believe that Congress should focus on bipartisan efforts to investigate the causes of and lessen the potential for gun violence in America, rather than the Hearing Protection Act," he said.

"I’d like to see what the investigation into the shooting in Las Vegas reveals and whether a suppressor would have allowed this monster to create even more carnage."

On the floor Wednesday, DeFazio said he believes the Republican leadership should formally withdraw the sportsman bill, which he said has "many objectionable provisions."

The SHARE Act passed the House last session, but that was without the inclusion of the Hearing Protection Act.

While the bill could still pass the House, the Senate could prove difficult.

If the bill were to pass out of committee, it would still need the support of at least eight Senate Democrats to overcome a filibuster.

Sen. Mike Crapo Michael (Mike) Dean CrapoBottom line Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump Top GOP senator urges agencies to protect renters, banks amid coronavirus aid negotiations MORE (R-Idaho) said he hopes to get a committee hearing on the companion bill he offered in the Senate earlier this year and then see the legislation move to the floor.

But Crapo wouldn’t guarantee the measure could get the necessary 60 votes on the floor.

“I hope so, but I’m not going to predict,” he said.

Still, he pushed back against Clinton and other critics who claim suppressors will make shootings like Las Vegas more deadly.

"I know the people have tried to tie the two together, but I don’t think it’s a legitimate point,” he said.

“The notion that a sound suppressor, which is to protect the hearing of the individual who is engaged in shooting sports, is somehow able to do the kinds of things you see in movies where James Bond can silently move through the night just isn’t actually accurate.”

Sen. Chris Murphy Christopher (Chris) Scott MurphyDemocratic senator calls for 'more flexible' medical supply chain to counter pandemics The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon GOP chairman to release interim report on Biden probe 'in about a week' MORE (D-Conn.), who has been leading the push to expand background checks for gun sales, doubts the bill will pass through Congress.

“I don’t think it had much chance before Las Vegas and I think it has even less chance now,” he said.

“The NRA clearly wants something for their support of the president and Republicans in Congress, but I’m confident we can get the votes to stop that,” he said.