Silencer (firearms)

A typical silencer is a metallic (usually stainless steel or titanium) cylinder containing numerous internal sound baffles, with a hollow bore to allow the bullet to exit normally.

During firing, the bullet passes through the bore with little hindrance, but most of the expanding gas ejecta behind it is redirected through a longer and convoluted escape path created by the baffles, prolonging the release time.

[11] Silencers were regularly used by agents of the United States Office of Strategic Services, who favored the newly designed High Standard HDM .22 LR pistol during World War II.

OSS Director William Joseph "Wild Bill" Donovan demonstrated the pistol for President Franklin D. Roosevelt at the White House.

According to OSS research chief Stanley Lovell,[12] Donovan, an old and trusted friend of the President, was waved into the Oval Office, where Roosevelt was dictating a letter.

When Roosevelt finished, Donovan turned his back and fired a shot into a sandbag he had brought with him, announced what he had done and handed the smoking gun to the astonished president.

[25][26][10][20] The Oxford, American Heritage, and other dictionaries apply the term suppressor to such contexts as electromagnetic shielding devices, genetics, and censorship, but not firearms.

[31][17] Along with state and federal legislative lobbying efforts, the NRA and ASA began public information campaigns designed to change the perception of silencers from their association with espionage, assassination, crime or military special operation use, to instead show that silencers can have health and safety benefits, primarily protecting the hearing of shooters and people in the vicinity, and to debunk the perceived myth in popular television, film and video game media that silencers are so effective that gunshot sounds can go totally unnoticed, such as by people in the next room of a building.

[33] Gun control advocates have said that changing the name from "silencer" to "suppressor" is semantic propaganda similar to the efforts to avoid terms like "assault rifle" or "assault weapon" in favor of friendlier-sounding language like "modern sporting rifle", while gun-rights advocates make essentially the opposite argument, and also that the widespread term silencer reflects technical ignorance and is poorly defined.

A gunshot (the combination of the sonic boom, the vacuum release, and hot gases) will almost always be louder than the sound of the action cycling of an autoloading firearm.

Alan C. Paulson, a renowned firearms specialist, claimed to have encountered an integrally suppressed .22 LR gun that had such a quiet report.

[34] Properly evaluating the sound generated by a firearm can be done only with a decibel meter in conjunction with a frequency spectrum analyzer during live tests.

[35] Both types of silencers reduce noise by allowing the rapidly expanding gases from the firing of the cartridge to be decelerated and cooled through a series of hollow chambers.

Often, a single, larger expansion chamber is located at the muzzle end of a can-type silencer, which allows the propellant gas to expand considerably and slow down before it encounters the baffles or wipes.

Some modern suppressors using steel or high-temperature alloy baffles can endure extended periods of fully automatic fire without damage.

[38] Wipes, packing materials, and purpose-designed wet cans have been generally abandoned in 21st-century suppressor design because they decrease overall accuracy and require excessive cleaning and maintenance.

The Russian AN-94 assault rifle has a muzzle attachment that claims apparent noise reduction by venting some gases through a "dog-whistle" type channel.

However, these concepts are controversial because a muzzle blast creates broadband noise rather than pure tones, and phase cancellation in particular is therefore extremely difficult (if not impossible) to achieve.

[46] The large calibre allows the bullet to be fired at subsonic speed, eliminating a major source of noise, while retaining accuracy, range, and effectiveness.

Semi-automatic and fully automatic firearms also make distinct noises as their actions cycle, ejecting the fired cartridge case and loading a new round.

Such effects may disorient the shooter, affecting situational awareness, concentration and accuracy, and can permanently damage hearing very quickly.

However, counter-sniper tactics can include gunfire locators, such as the U.S. Boomerang system, where sensitive microphones are coupled to computers running algorithms, and use the ballistic crack to detect and localize the origin of the shot.

Hunters using centerfire rifles find silencers bring various important benefits that outweigh the extra weight and resulting change in the firearm's center of gravity.

In the field, however, the comparatively large size of a centerfire rifle suppressor can cause unwanted noise if it bumps or rubs against vegetation or rocks, so many users cover them with neoprene sleeves.

While this is similar to the energy available from the .45 ACP pistol cartridge, the reduced diameter, and streamlined shape of the heavy .30 caliber bullet provides far better external ballistic performance, improving range substantially.

[35] Live tests by independent reviewers of numerous commercially available suppressors find that even low-power, unsuppressed .22LR handguns produce gunshots over 160 decibels.

[63] The De Lisle carbine, a British World War II suppressed rifle used in small numbers by Special Forces, was recorded at 85.5 dB in official firing tests.

[65] For additional comparison, chainsaws, rock concerts, rocket engines, pneumatic drills, small firecrackers, and ambulance sirens are rated between 100 and 140 dB.

[16] Traditional measures of suppressor noise reduction have focused on the change in the peak sound pressure level between suppressed and unsuppressed conditions.

In MIL-STD 1474D, materiel that produced peak levels below 140 dB were not subject to a requirement to wear hearing protection devices that could affect a person's situational awareness.