Gun silencer sales in the United Sates are exploding as firearms owners are looking to accessorize.

Silencer sales to civilians shot up 37% in 2013 to nearly 500,000 units, increasing from 360,000 in 2012 and 285,000 in 2011, CNNMoney reports. There’s now a nine-month wait to register silencers with the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF).

The silencer buying frenzy is the second wave of gun-related purchases in the last two years. After the Newtown massacre, gun owners feared that a weapons ban would be enacted and rushed to buy assault rifles. Now that last year’s push for universal background checks has failed, gun owners have a lot of guns on their hands, and are outfitting them with gadgets including silencers, flashlights, laser scopes, stocks, pistol grips and rail systems.

“People have gone crazy buying guns, but they’re done buying them for the time being, so they’re buying accessories,” Ben Shim, a firearms instructor and gun industry analyst with CRT Capital Group told CNNMoney.

Silencers are regulated by the 1934 National Firearms Act, and are legal in 39 states. While purchasing a gun requires a photo ID and an electronic form submitted to the ATF, purchasing a silencer requires applicants to mail a photo and fingerprints to the ATF and pay a $200 tax. And they often cost more than guns, approaching prices over $1,000.

The thought of a silenced gun conjures up the image of a black-gloved hand wielding a smoking pistol in some grimy back alley, but advocates say they’re in demand because they allow hunters to fire multiple shots without frightening game. “Silencing is not a crime,” is the slogan of Georgia-based Advanced Armament Corp.

[CNNMoney]

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