Gun silencers have been one of the most tightly regulated firearms products in the United States since 1934. Now Congress may eliminate those restrictions, which everybody agrees could mean millions more silencers in the hands of American gun owners.

The debate is whether the benefits of more silencers would outweigh the costs.

Silencers, also called suppressors, are restricted under the National Firearms Act, alongside weaponry like machine guns and sawed-off shotguns. Federal regulations impose a high barrier to purchase: Buyers must pay a $200 transfer fee, submit to fingerprinting and pass a federal background check, a process that can take up to nine months to complete.

Lawmakers say their push to end those requirements and thereby make silencers more easily available is about protecting the hearing of gun owners exposed to high-volume blasts while hunting or target shooting. They are calling their bill the Hearing Protection Act, and it is currently awaiting committee hearings in the House and Senate.

“This legislation is about safety ― plain and simple,” said Rep. Jeff Duncan (R-S.C.), one of the bill’s sponsors, in a January statement. “I’m very active in sport shooting and hunting, and I can’t tell you how better off the shooting sports enthusiasts would be if we had easier access to suppressors to help protect our hearing.”

A similar bill failed to make it out of committee in 2015, but now that Republicans are in control of the White House and both chambers of Congress, the measure has a much better chance of passing. Donald Trump Jr., the president’s son, has put his support behind the effort, saying in an interview with the CEO of manufacturer SilencerCo last fall that the current regulations were “just another rule the government wants to put in place for no reason.”

Advocates for gun violence prevention say the bill is a gift to the firearms industry, because it would massively expand the market for silencers, and to criminals, because it would make it easier to fire a gun undetected.

Silencers are “used to conceal the fact that you are firing a weapon,” said Sen. Chris Murphy (D-Conn.). “There will be more crimes committed, more people killed” if the current bill passes.

Illustration: HuffPost/Photos: Getty Images “This legislation is about safety -- plain and simple,” said Rep. Jeff Duncan, a sponsor of the Hearing Protection Act.

American engineer Hiram Percy Maxim patented the first silencer in the early 1900s, using technology that he would later apply in developing an automobile muffler. That basic concept hasn’t changed much since. The cylindrical device screws on to the barrel of a gun. Chambers within the silencer allow gases to dissipate and cool after escaping from the muzzle, which damps sound emissions.

Initial suppressor models were reportedly unpopular and controversial. Fearing they could encourage crime, states began cracking down on their use. The federal government placed them on a list of regulated devices under the National Firearms Act during the Great Depression, amid concerns that people might use them to avoid detection while illegally hunting for food.

Suppressor technology made substantial leaps in the Vietnam War era, thanks to a former CIA dark-ops contractor named Mitch WerBell. His silencers were more compact and effective than their predecessors. They attracted the attention of U.S. military and intelligence agencies, which reportedly began using them to carry out targeted killings. WerBell became known in some gun enthusiast circles as the “Wizard of Whispering Death.”

Most people today probably envision silencers based on their Hollywood depiction: An assassin fits the attachment to the end of his weapon, which he then fires with a muffled “pew” instead of a bang.

Silencer manufacturers emphasize this is an inaccurate representation. Depending on the weapon, unsuppressed gunfire typically ranges between 140 and 160 decibels ― volumes that can rupture eardrums and cause permanent hearing loss. Silencers make shooting quieter, but they don’t make it quiet, said Jason Schauble, chief revenue officer at Utah-based SilencerCo.

“Suppressors are really about taking shooting noise below 140 decibels, which is the OSHA hearing-safe level,” Schauble said. “Many suppressors end up around 130 or 120 decibels, so around the volume of a car door slamming.”

At the level, more hunters would likely choose to shoot without ear protection, making it easier for them to hear animals or have conversations with companions. Lowering the sound of gunfire would also reduce hearing hazards related to sport shooting and lessen noise pollution around shooting ranges.

Here’s a demonstration from SilencerCo:

Not everyone is convinced that shooting-related hearing loss is a problem that needs another solution.

“You already have the answer,” said Kris Brown, chief strategy officer at the Brady Campaign to Prevent Gun Violence. “There are things available on the market to protect hearing.”

The people who want to make silencers more easily available point to a range of other tactical benefits. Silencers decrease a weapon’s recoil and improve its accuracy, the American Suppressor Association says on its website. This lets shooters fire in rapid succession without losing track of the target, as silencer manufacturers note. Suppressors also reduce muzzle flash, allowing shooters to better disguise their location in low-light settings.

Although supporters of silencers tout these latter advantages in terms of sport shooting, the same characteristics might also appeal to a mass shooter or other criminal.

“There could be some instance where somebody uses it for nefarious purposes,” said Jack Rinchich, president of the National Association of Chiefs of Police. “They don’t want a loud report or a muzzle flash or a blast ― say a sniper or someone trying to shoot at police officers or other people from a distance ― and they want to suppress that noise.”

The National Association of Chiefs of Police has not taken an official position on the bill.

Not Popular With Criminals ― Yet

About 1.3 million silencers are currently registered in the U.S., the Justice Department said in February, which is nearly 400,000 more than in 2015. Buyers have to go through the federal registration process to purchase them in the 42 states where they are legal.

Some data suggest that silencers are rarely used in crimes. Over the past decade, the Bureau of Alcohol, Tobacco, Firearms and Explosives has referred very few silencer-related cases for prosecution, according to a white paper proposal written by the ATF’s second highest-ranking official in January.

“Silencers are very rarely used in criminal shootings,” states the paper, which The Washington Post obtained last month. “Given the lack of criminality associated with silencers, it is reasonable to conclude that they should not be viewed as a threat to public safety.”

Rinchich noted that in his four decades in law enforcement, he doesn’t recall ever finding a gun used in a crime with a silencer.

Gun control advocates argue those statistics are proof of the effectiveness of existing regulations, not a reason to undo them. They point to a handful of known crimes committed with silencers to show there is at least some risk of criminal behavior.

Jim Urquhart/Reuters SilencerCo CEO Joshua Waldron fires a rifle with a suppressor in West Valley City, Utah, on Feb. 23, 2016.

But gun lobbyists argue that suppressors will never be a natural choice for criminals.

“The majority of firearms used in crimes are small, concealable handguns,” said Knox Williams, president of the American Suppressor Association. “Folks want to be able to put something in a pocket or hide it in a waistband. When you add a suppressor to that, you’re generally adding 6 to 8 inches to the length of a gun.”

On top of being unwieldy, silencers are also expensive, ranging from a few hundred to more than a thousand dollars depending on the category of firearm and type of suppressor.

“People don’t buy a thousand-dollar thing to add to another thousand-dollar thing so they have a really nice gun-and-silencer combination to commit crime,” Schauble said.

If silencers become more easily available, however, supporters admit that the current low levels of related criminal activity could rise.

“There are always going to be a couple people who misuse any tool contrary to its intended use, whether it be sound suppressors, whether it be firearms, whether it be motor vehicles,” Schauble said. “It’s an emotional issue, and like most issues that are emotional, it’s emotional because no one really knows what will happen.”

Silencers could also prove problematic for gunshot detectors, which use decibel levels to identify the sound of firearms. And that troubles some law enforcement officials.

“Cities all over the country have invested a lot of money in gunshot detectors because people shooting firearms in a community is a problem, and it allows the police to know that’s taken place and to respond even if nobody’s called,” said Darrel Stephens, executive director of the Major Cities Chiefs Association.

Dreaming Of A Business Boom

With an estimated 300 million firearms in civilian hands in the U.S., silencer manufacturers see huge potential for their product. Even under the current restrictions, suppressors have grown more popular over the last several years.

SilencerCo’s business has increased 600 percent since 2014, with more than 100,000 sales last year, almost all to civilians, according to Schauble. He believes that with deregulation, the market could expand as much as tenfold, leading to the sale of more than a million silencers each year. After all, some 299 million guns don’t have silencers yet.

Lawmakers who oppose the bill say that is the real push behind the legislation. “The gun industry is faced with a declining number of Americans that are buying guns, so they have to target more weapons and more expensive weapons to that smaller number of Americans,” said Murphy.

That would fit a longstanding pattern of the gun lobby dismissing potential public safety consequences in its campaign to loosen gun laws, critics contend. Last month, congressional Republicans voted to repeal a measure that had blocked some Social Security disability insurance recipients from purchasing firearms. GOP lawmakers called it an undue infringement upon the rights of Americans with disabilities, but supporters said the rule was necessary to keep guns out of the hands of mentally ill individuals. In recent years, state and federal lawmakers have also offered a number of proposals to roll back permitting and training requirements for those who want carry guns.

“It’s a continual process of making guns ubiquitous in America,” said Stephens.

CORRECTION: Sen. Chris Murphy was previously misidentified as a member of the House of Representatives.