A suppressor, also commonly known as a silencer is a device attached to a firearm to reduce the amount of noise and flash generated by firing the weapon. Suppressors work much like an automotive muffler, reducing the amount of audible noise caused by the release of high pressure gas when the bullet exits the barrel (see internal ballistics). The term "silencer" is inaccurate as suppressors lessen the sound of a firearm's muzzle blast only, the cannot completely eliminate the sound of firing. The near silent suppressed firearms seen in movies and television is pure fabrication; the most effective suppressors at most reduce sound to the level of a cough, and for all but the smallest rimfire calibers, those suppressors are far larger than those depicted.
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History and legal status
Early suppressors were created around the beginning of the 20th century by a number of inventors. American inventor Hiram P. Maxim is credited with inventing and selling the first commercially successful models from around 1902.
Legal regulation of suppressors varies widely around the world. In some nations, such as England or Finland, they are practically unregulated and may be bought "over the counter" in retail stores. Other nations, such as Canada, practically forbid their private citizens from owning silencers, while yet others, such as the USA, tax and regulate their manufacture and sale. In the United States, it is illegal to make, possess, buy, sell, or trade a silencer except to other Category III firearm license holders; such transfers also require payment of a $200 tax and a significant background check. The effect is to practically ban such items, for an item that might cost less than $10 to manufacture. Some states go further, and explicitly ban any civilian possession of suppressors.
Despite common misconception that suppressors violate the laws of war, special forces have made use of suppressed firearms in warfare worldwide since their invention. One of the more famous, and most effective, suppressed firearms was the British De Lisle carbine developed in WWII. During the late 1950s the PLA procured millions of domestically produced clones of the PPSh submachine gun with integrated silencer for infantry use.
Suppressor design and construction
The suppressor is typically a cylindrical piece of machined metal that attaches to the muzzle of the pistol or rifle. Some others are designed as an integral part of the weapon, and may include an expansion chamber that partially surrounds the barrel (these are often called "telescoping" designs, a referece to old-fashioned collapsing telescopes). The suppressor reduces noise by allowing the rapidly expanding gasses from the detonation of the round to be briefly diverted or trapped inside a series of hollow chambers called baffles. Some advanced designs use baffles to shift the frequency of the remaining sound beyond the range of human hearing, further reducing noise. Other types, called "wet" suppressors or "wet cans", use a small quantity of water, oil, or grease in the first chamber to cool the powder gasses and reduce the volume (see ideal gas law). The coolant lasts only a few shots before it must be replenished, but while it lasts it can greatly increase the effectiveness of the supressor. One manufacturer claims a 30% improvement in sound suppression for "4 magazines" (32 to 68 rounds) with the addition of 5 ml of water or light oil to their suppressor. Water is most effective, due it its high heat of vaporization, but it can leak or evaporate out of the suppressor. Grease, while messier and less effective than water, can be left in the suppressor indefinitely without losing effectiveness. Oil is the least effective, as it leaks like water and is as messy as grease, leaving behind a fine mist of condensed oil after each shot.
Suppressors vary greatly in size and efficiency. A type developed in the 1980s by the US Navy for 9 mm pistols is 15 cm by 4.5 cm (5.9 in. X 1.77 in.) and is good for six shots with standard ammunition or up to thirty with low-powered, subsonic ammunition. The British Sterling suppressor is 35 cm (13.78 in.) long and 7.5 cm (2.95 in.) in diameter and will work effectively for hundreds of shots with standard ammunition. Generally the longevity of a suppressor is based on the material used for the baffles. Rubber baffles that are smaller than the bullet diameter are best, as they trap the most gas, but they wear quickly and lose effectiveness. Steel or aluminum baffles last far longer, but are less efficient to begin with.
Suppressors can be improvised with any baffling material (pillow, potato, plastic bottle etc); these are only marginally useful.
Ammunition for use with suppressors
Suppressors are most effective when the bullet's velocity does not exceed the speed of sound. A bullet that breaks the sound barrier creates loud flight noise, or a "sonic boom". As velocity increases further beyond the speed of sound, flight noise does not increase significantly. Supersonic flight noise may be reduced somewhat by using a projectile of smaller caliber. Bullets that travel near the speed of sound are considered transsonic, which means that the airflow over the surface of the bullet, which at points travels faster than the bullet itself, can break the speed of sound. Pointed bullets which gradually displace air can get closer to the speed of sound than round nosed bullets before becoming transonic.
Firearms for use with suppressors
The type of gun also effects suppressor efficiency. Guns with the least 'leakage' are best, so a sealed breech (e.g. bolt action) is preferable and can be suppressed to the point that the "click" as the striker or hammer falls is the loudest sound of firing. Most autoloading firearms still produce a significant amount of noise from the gun cycling (a video is available here) and the leak of high velocity gas from the breech. Revolvers, due to their 'loose' structure, cannot be made quiet, with few exceptions: the Nagant M1895 revolver, used an unusual gas-sealed cylinder that made it suitable for use with a suppressor.
While it seems that any semiautomatic pistol could be fitted with a suppressor, it's not as easy as just threading the barrel and screwing one on. Most semiautomatic pistols in larger calibers, 9 x 19 mm Parabellum and larger, use a short recoil action. This means that the slide and barrel both recoil backwards for a short distance before the slide unlocks from the barrel, allowing the round to be ejected. This is done to keep the breech sealed until the chamber pressure drops to safe levels. Adding the mass of a suppressor to the mass of the recoiling parts means that it will significantly alter the operation of the gun; in most cases, it stops the slide from unlocking at all, and effectively turns the semiautomatic pistol into a bolt action. This is not always a bad thing, however, as the sound of the action cycling is often louder than the suppressed shot. In addition to this, nearly all short recoil designs are based on the Browning tilting link action, as used in the M1911. This system uses a tilting barrel, which means that in addition adding mass, the suppressor also adds rotational inertia, greatly resisting the force that tilts the barrel. Because of the high pressures and close tolerances required, the suppressor cannot be allowed to bend at the joint, or the bullet would hit the baffles rather than passing through the middle. Special mechanisms, called "recoil enhancers" or "Nielsen devices", are used to decouple the mass of the suppressor from the barrel. These consist of a sliding baffle in the rear of the suppressor that is forced back under the pressure of the powder gas, thus forcing the barrel backwards and unlocking the short recoil mechanism. Adding one of these mechanisms increases the complexity and cost of the suppressor.
Because of the difficulties of suppressing short action designs, suppressors are easiest to add to smaller caliber pistols. .380 ACP and .22 Long Rifle are both usually blowback designs with fixed barrels, and are easy to suppress. The most commonly suppressed firearms are .22 Long Rifle semiautomatic pistols and rifles; suppressing the firearms allows them to be fired without use of hearing protection. Subsonic rounds are readily available in .22 Long Rifle, and even with supersonic rounds the crack of firing is not uncomfortable.
Specially designed firearms with integral suppressors provide the best overall result, as the suppressor can be fully telescoped to reduce the overall length of the gun, and the caliber can be chosen for maximum performance with the suppressor. .45 ACP is an ideal choice, since the standard 230 grain loading is both powerful and subsonic. Special cartridges are also available designed for use with suppressors. The .300 Whisper is probably the most common of these. It is made by cutting a 5.56 mm NATO cartridge down to a shorter length, then increasing the neck to accommadate a .30 caliber (7.62mm) bullet. It is loaded with a heavy bullet (over 200 grains) at subsonic velocities. This gives it the muzzle energy of the .45 ACP with a far better ballistic coefficient (see external ballistics) for better long range performance. The use of the 5.56mm NATO as a base case means that it can be chambered in M-16 derived rifles with a simple barrel change. In addition to special applications in suppressed firearms, the .300 Whisper has become popular with metallic silhouette shooters due to its low recoil, good long range performance, and very good accuracy.
While suppressors are most accurate with subsonic cartridges, they can be used effectively with supersonic cartridges. The crack of the supersonic bullet cannot be avoided, but the suppressor will reduce the sound of the muzzle blast, and make it more difficult to locate the source of the shot by sound. Suppressors are most effective to the side and rear of the shooter, so a suppressor could be used by a sniper effectively. Observers not in the target area would hear the least, and the crack of the arriving bullet will tend to obscure the location from the area of the target.