A suppressor, sound suppressor, sound moderator, or silencer, is a device either attached to or part of the barrel of a firearm to reduce the amount of noise and flash generated by firing the weapon. Although suppressors are popularly known as silencers, no suppressor completely eliminates the noise of discharging a firearm.

It generally takes the form of a cylindrically shaped metal tube with various internal mechanisms to reduce the sound of firing by slowing the escaping propellant gas and sometimes by reducing the velocity of the bullet.

History

Early suppressors were created around the beginning of the 20th century by several inventors. American inventor Hiram Maxim is credited with inventing and selling the first commercially successful models circa 1902. Maxim gave his device the trademarked name Maxim Silencer. The muffler for internal combustion engines was developed in parallel with the firearm suppressor by Maxim in the early 20th century, using many of the same techniques to provide quieter-running engines. Indeed, in many European countries, automobile mufflers are still referred to as "silencers." The term silencer has since fallen out of favor among the firearms industry, being replaced with the more accurate term sound suppressor or just suppressor. Common usage and U.S. legislative language favor the historically earlier term, silencer. In U.S. law, the terms "firearm muffler" and "firearm silencer" are synonymous.

Suppressors were regularly used by United States Office of Strategic Services agents during World War II, who favored the newly-designed High Standard HDM .22 Long Rifle pistol. OSS Director "Wild Bill" Donovan demonstrated the pistol for President Franklin D. Roosevelt at the White House. According to OSS research chief Stanley Lovell, Donovan (an old and trusted friend of the President) was waved into the Oval Office, where Roosevelt was dictating a letter. While Roosevelt finished his message, Donovan turned his back and fired ten shots into a sandbag he had brought with him, announced what he had done and handed the smoking gun to the astonished president.

Design and construction

The suppressor is typically a hollow cylindrical piece of machined metal (steel, aluminium, or titanium) containing expansion chambers that attaches to the muzzle of a pistol, submachine gun or rifle. These "can"-type suppressors (so-called as they resemble a beverage can), may be detached by the user and attached to a different firearm of the same caliber. Another type is the "integral" suppressor, which consists of expansion chambers surrounding the barrel. The barrel is pierced with openings or "ports" which bleed off gases into the chambers. This type of suppressor is part of the firearm, and maintenance of the suppressor requires that the firearm be at least partially disassembled.

Both types of suppressor reduce noise by allowing the rapidly expanding gases from the firing of the cartridge to be briefly diverted or trapped inside a series of hollow chambers. The trapped gas expands and cools, and its pressure and velocity decreases as it exits the suppressor. The chambers are divided by either baffles or wipes (see below). There are typically at least four and up to perhaps fifteen chambers in a suppressor, depending on the intended use and design details. Often, a single, larger expansion chamber is located at the muzzle end of a can-type suppressor, which allows the propellant gas to expand considerably and slow down before it encounters the baffles or wipes. This larger chamber may be "reflexed" toward the rear of the barrel to minimize the overall length of the combined firearm and suppressor, especially with longer weapons such as rifles.

Suppressors vary greatly in size and efficiency. One disposable type developed in the 1980s by the U.S. Navy for 9 mm pistols was long and in outside diameter, and was designed for six shots with standard ammunition or up to thirty shots with subsonic (slower than the speed of sound) ammunition. In contrast, one suppressor designed for rifles firing the powerful .50 caliber cartridge is long and in diameter.

Components

Baffles are circular metal dividers which separate the expansion chambers. Each baffle has a hole in its center to permit the passage of the bullet through the suppressor and towards the target. The hole is typically at least 0.04 inch (1 mm) larger than the bullet caliber to minimize the risk of the bullet hitting the baffle ("baffle strike"). Baffles are typically made of stainless steel, aluminium, titanium or alloys such as Inconel, and are either machined out of solid metal or stamped out of sheet metal. A few suppressors for low-powered cartridges such as the .22 Long Rifle have successfully used plastic baffles (certain models by Vaime and others.)

Baffles are separated by spacers, which keep them aligned at a specified distance apart inside the suppressor. Many baffles are manufactured as a single assembly with its spacer, and several suppressor designs have all the baffles attached together with spacers as a one-piece helical baffle stack. Modern baffles are usually carefully shaped to divert the propellant gases effectively into the chambers. This shaping can be a slanted flat surface, canted at an angle to the bore, or a conical or otherwise curved surface. One popular technique is to have alternating angled surfaces through the stack of baffles.

Baffles usually last for a significant number of firings. Propellant gas heats and erodes the baffles, causing wear, which is worsened by high rates of fire. Aluminium baffles are seldom used with fully automatic weapon, because service life is unacceptably short. Some modern suppressors using steel or high-temperature alloy baffles can endure extended periods of fully-automatic fire without damage. The highest-quality rifle suppressors available today have a claimed service life of greater than 30,000 rounds.

Wipes are inner dividers intended to touch the bullet as it passes through the suppressor, and are typically made of rubber, plastic or foam. Each wipe may either have a hole drilled in it before use, a pattern stamped into its surface at the point where the bullet will strike it, or it may simply be punched through by the bullet. Wipes typically last for a small number of firings (perhaps no more than five) before their performance is significantly degraded. While many suppressors used wipes in the Vietnam War era, most modern suppressors do not use them to minimize disassembly and parts replacement.

"Wet" suppressors or "wet cans" use a small quantity of water, oil, grease or gel in the expansion chambers to cool the propellant gases and reduce their volume (see ideal gas law). The coolant lasts only a few shots before it must be replenished, but can greatly increase the effectiveness of the suppressor. Water is most effective, due to its high heat of vaporization, but it can run 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 and least preferable, as it runs while being as messy as grease, and leaves behind a fine mist of aerosolized oil after each shot. Water-based gels, such as wire-pulling lubricant gel, are a good compromise; they offer the efficacy of water with less mess, as they do not run or drip. However, they take longer to apply, as they must be cleared from the bore of the suppressor to ensure a clear path for the bullet (grease requires this step as well). Generally, only pistol suppressors are shot wet, as rifle suppressors handle such high pressure and heat that the liquid is gone within 1-3 shots. Many manufacturers will not warranty their rifle suppressors for "wet" fire, as some feel this may even result in a dangerous over-pressurization of the silencer.

Packing materials such as metal mesh, steel wool or metal washers may be used to fill the chambers and further dissipate and cool the gases. These are somewhat more effective than empty chambers, but less effective than wet designs. Metal mesh, if properly used, may last for hundreds or thousands of shots of spaced semi-automatic fire, however steel wool usually degrades within ten shots with stainless wool lasting longer than regular steel wool. Like wipes, packing materials are rarely found in modern suppressors.

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 instructions from several manufacturers state that their suppressors need not be cleaned at all. Furthermore, legal changes in the United States during the 1980s and 1990s made it much more difficult for end-users to legally replace internal silencer parts, and the newer designs reflect this reality.

Advanced types

In addition to containing and slowly releasing the gas pressure associated with muzzle blast or reducing pressure through the use of coolant mediums, advanced suppressor designs attempt to modify the properties of the sound waves generated by the muzzle blast. In these designs, effects known as frequency shifting and phase cancellation (or destructive interference) are used in an attempt to make the suppressor quieter. These effects are achieved by separating the flow of gases and causing them to collide with each other. The intended effect of frequency shifting is to shift audible sound waves frequencies into ultrasound (above 20 kHz), beyond the range of human hearing. Phase cancellation occurs when similar sound wave frequencies encounter each other 180° out of phase, canceling the amplitude of the wave and eliminating the pressure variations perceived as sound.

Utilizing either effect to an advantage requires that the suppressor be designed with specific properties of the muzzle blast in mind. For example, the velocity of the sound waves are a major factor. This figure can change significantly between different cartridges and barrel lengths. Thus, in order for maximum effectiveness to be achieved, the suppressor must be "tuned" for a specific cartridge/barrel length combination. This can be done through the use of either a fixed or adjustable baffle design.

However, these concepts are controversial because muzzle blast creates broadband noise rather than pure tones, and phase cancellation in particular is therefore extremely difficult (if not impossible) to achieve. Some suppressor manufacturers claim to utilize phase cancellation in their designs, but these claims are generally unsupported from a scientific perspective.

Effectiveness for volume

The portrayal of suppressed firearms in movies is not always accurate and could lead to the misconception that silencers are capable of completely eliminating the sound of firing, or reducing it to a quiet whistling or "phut" sound. This is because when a gun is fired, multiple sounds are made (in order of timing):

• the bolt/hammer sliding or pivoting forward to the cartridge
• the firing pin striking the cartridge
• the burn of powder and particulates, especially with larger calibers
• the violent expansion of gases coming out of the barrel
• the bolt/hammer sliding or pivoting back from the cartridge (in a semi- or fully-automatic firearm)
• the sonic boom created by common supersonic ammunition
• the rotating and locking of the cylinder (on revolvers), or the spring/gas powered loading of the next cartridge (on non-revolver firearms)
• the slide locking back when the magazine is empty (on non-revolver firearms)
• the bullet colliding with the target

Obviously, some of these sounds are much louder than others. The two loudest sounds in a gunshot are typically the expansion of gases and the sonic boom. Multiple techniques are used to address each of these sounds, but the suppressor itself usually only addresses the sound due to the violent expansion of gases and associated burn, although some suppressors address the sonic boom by reducing the speed of the bullet while traveling down the barrel.

Real world data

Live tests by independent reviewers of numerous commercially available suppressors find that even low caliber unsuppressed .22 LR firearms produce gunshots over 160 decibels. In testing, most of the suppressors reduced the volume to between 130 and 145 dB, with the quietest suppressors metering at 117 dB. The actual suppression of sound ranged from 14.3 to 43 dB, with most data points around the 30 dB mark.

Comparatively, ear protection commonly used while shooting provides 18 to 32 dB of sound reduction at the ear. Further, chainsaws, rock concerts, rocket engines, pneumatic drills, small firecrackers, and ambulance sirens are rated at 100 to 140 dB.

While some consider the noise reduction of a suppressor significant enough to permit safe shooting without hearing protection ("hearing safe"), noise induced hearing loss occurs at 85 dB or above, and suppressed gunshots regularly meter above 130 dB. However, the US Occupational Safety and Health Administration uses 140 dB as the "safety cutoff" for impulsive noise, which has led most US manufacturers to advertise sub-140 dB suppressors as "hearing safe."

Caliber versus volume

The caliber and power of the bullet/cartridge being suppressed is also an important factor. Generally, equal quality suppressors can quiet the report of a smaller caliber bullet more effectively than a larger caliber bullet. This is because the exhaust gases can move more quickly through the exit hole necessary for larger caliber bullets. Likewise, cartridges which produce higher pressures and more gasses, such as those used in rifles, will also generally be louder than those which produce less pressure and fewer gasses, such as handgun cartridges. In a gunshot, the sound of the report (the combination of the sonic boom, the vacuum release, and burn of powder) will almost always be louder than the sound of the action cycling of a auto-loading firearm. Alan C. Paulson, a renowned firearms specialist, claimed to have encountered an integrally suppressed .22 LR that had such a quiet report, although this is somewhat uncommon.

Because of the limited stopping power of less powerful cartridges, movie scenes in which an attacker fires a near-silent shot that instantly kills the victim are generally unrealistic.

Subsonic ammunition versus volume

In weapons firing supersonic bullets, the supersonic bullet itself produces a loud and very sharp sound as it leaves the muzzle in excess of the speed of sound and gradually reducing speed as it travels downrange. This is a small sonic boom, and is referred to in the firearm field as "ballistic crack". Subsonic ammunition reduces this sound, but at the cost of lower velocity, often resulting in decreased range and effectiveness on the target. Military marksmen and police units may use this ammunition to maximize the effectiveness of their silenced rifles. While the range may be decreased when using subsonic rounds, this may be acceptable for specialized situations, where the absolute minimum amount of noise is required.

However, the numeric effectiveness of subsonic rounds is, again, misrepresented by Hollywood. Independent testing of commercially available firearm suppressors with commercially available subsonic rounds has found that .308 subsonic rounds decreased the volume at the muzzle 10 to 12 dB when compared to the same caliber of suppressed supersonic ammunition. When combined with suppressors, the subsonic .308 rounds metered between 121 and 137 dB.

This ballistic crack depends on the speed of sound, which in turn depends mainly on air temperature. At sea level, an ambient temperature of 70 °F (21 °C), and under normal atmospheric conditions, the speed of sound is approximately 1140 feet per second (347 m/s). Bullets that travel near the speed of sound are considered transonic, 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.

Because merely reducing the propellant in a cartridge to get a slower bullet would lead to less stopping power, special cartridges have been developed specifically to maximize the energy available when used with a suppressor. These cartridges use very heavy bullets to make up for the energy lost by keeping the bullet subsonic. A good example of this is the .300 Whisper cartridge, which is formed from a necked-up .221 Remington Fireball cartridge case. The subsonic .300 Whisper fires up to a 250 grain (16.2 g), .30 caliber bullet at about 980 feet per second (298 m/s), generating about 533 ft·lbf (722 J) of energy at the muzzle. 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.

9x19mm Parabellum, a very popular caliber for suppressed shooting, can use almost any factory-loaded 147 gr (9.5 g) weight round to achieve subsonic performance. These 147 gr weight bullets typically have a velocity between 900 and 980 feet per second (275 and 300 m/s), which is less than the common 1140 ft/s speed of sound.

Instead of using subsonic ammunition, one can also lower the muzzle velocity of a supersonic bullet before it leaves the barrel. Some suppressor designs do this by allowing gas to bleed off along the length of the barrel before the projectile exits; others contain wipes that use friction to slow the bullet before exiting. However, wipes generally wear out and lose effectiveness after relatively few shots, and the bleed-off designs require periodic cleaning.

Identification

Aside reductions in volume, suppressors also tend to alter the sound to something that is not identifiable as a gunshot. This reduces or eliminates attention drawn to the shooter (hence the Finnish expression: "A silencer does not make a marksman silent, but it does make him invisible"). This is especially true in cases where there are other sources of ambient noise, such as in an urban environment. Suppressors are particularly useful in enclosed spaces where the sound, flash and pressure effects of a weapon being fired are amplified. Such effects may disorient the shooter, affecting situational awareness, concentration and accuracy, and can permanently damage hearing very quickly.

As the suppressed sound of firing is overshadowed by ballistic crack, observers can be deceived as to the location of the shooter, often from 90 to 180 degrees from his actual location. However, counter-sniper tactics can include Gunshot Location Detection Systems, where sensitive microphones are coupled to computer algorithms, and use the ballistic crack to detect and localize the origin of the shot. The U.S. Boomerang system is currently the only deployed example.

Handgun versus longarm

The type of firearm to be suppressed also affects suppressor efficiency. Guns with the least gas leakage are best, so a sealed breech (e.g. bolt action or lever 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 semi- and fully-automatic firearms still produce a significant amount of noise from the gun cycling and the leak of high-velocity gas from the breech. Revolvers, due to the gap between the cylinder and barrel, cannot be made quiet. There are however, a few exceptions: The Nagant M1895 revolver uses an unusual cylinder that moves forward upon firing, and a special extended cartridge case which seals the gap between cylinder and barrel, making it suitable for use with a suppressor.

While it seems that any semi-automatic pistol can be fitted with a suppressor, it is not as simple as threading the barrel and installing a suppressor. Most semi-automatic pistols of 9 mm Luger caliber or larger use a short recoil action. In this system, the slide and barrel both recoil for a short distance before the slide unlocks from the barrel and opens the breech. This keeps the breech sealed until the chamber pressure drops to a safe level. Adding the mass of a suppressor to the barrel/slide combination will significantly alter the operation of the gun; in most cases, the added mass stops the slide from unlocking at all, and effectively turns the semi-automatic pistol into a single-shot weapon. This is not always undesirable, as the sound of the action cycling is often louder than the suppressed report. Nearly all short recoil designs are based on the John Browning-designed tilting barrel lockup, as used in the M1911, Browning Hi-Power and Glock pistols. This system uses a tilting barrel, which means that in addition to adding mass, the suppressor also adds rotational inertia, greatly resisting the force that tilts the barrel. Special mechanisms, called recoil boosters or Nielsen devices (shown in the photo gallery below), are used to decouple the mass of the suppressor from the barrel. These devices consist of a sliding piston 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 a recoil booster increases the complexity and cost of the suppressor, but enhances its ability to function in the semi-automatic mode. Many companies include an indexing system in the design of the Nielsen device which allows the suppressor to be oriented in a number of different longitudinal positions. This allows the user to fine-tune the weapon's point of aim; typically the user selects the setting which minimizes the impact shift between the suppressed and unsuppressed states.

Due to the difficulties of suppressing short recoil designs, suppressors are easier to add to smaller-caliber pistols, such as those chambered in .380 ACP, .32 ACP and .22 Long Rifle (.22 LR). Pistols using these cartridges are usually blowback designs with fixed barrels, which are easier to suppress. The most commonly suppressed firearms are .22 LR semi-automatic pistols and rifles, which allows them to be fired without the use of hearing protection, even with supersonic rounds. Specially-designed firearms with integral suppressors (e.g. the Welrod or De Lisle Carbine) 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. The .45 ACP is an excellent choice, since the standard 230 grain (15 g) loading is both powerful and subsonic.

Image:Nielsen_device_area_of_YHM_Cobra_.45_suppressor.jpg|Rear of a suppressor with the Nielsen device protruding (completely assembled).Image:Nielsen_device_of_YHM_Cobra_.45_suppressor_partially_removed.jpg|Retaining ring unscrewed and Nielsen device partially removed.Image:Nielsen_device_of_YHM_Cobra_.45_suppressor_completely_disassembled.jpg|Nielsen device completely removed and disassembled.Image:Rotational_indexing_system_of_YHM_Cobra_.45_suppressor_Nielsen_device.jpg|Rear of suppressor showing the rotational indexing system incorporated into some Nielsen devices.

Other advantages

There are many advantages in using a suppressor that are not related to the sound.

Hunters using centerfire rifles find suppressors bring various important benefits that outweigh the extra weight and resulting change in the firearm's center of gravity. By reducing noise, recoil and muzzle-blast, it enables the firer to follow-through calmly on his first shot and fire a further carefully-aimed shot without delay if necessary. Wildlife of all kinds are often confused as to the direction of the source of a well-suppressed shot. 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, and many users cover them with neoprene sleeves.

Suppressors can increase the precision of a rifle, as they strip away hot gases from around the projectile in a uniform fashion. The suppressor can reduce the recoil significantly as it traps the escaping gas. This gas mass is a little less than one-half the projectile mass (approximately 1.6 grams vs 4 grams for 5.56x45mm NATO ammunition), with the gas exiting the muzzle at about twice the projectile's velocity, thus giving a reduction in the felt recoil of approximately 15%. The added weight of the suppressor — normally 300 to 500 grams — also contributes to the reduction of the recoil, though a significantly heavy suppressor would unbalance a weapon. Further, the pressure against the face of each baffle is higher than the pressure on its reverse side, making each baffle a miniature "pneumatic ram" which pulls the suppressor forward on the weapon, which can contribute an immense force to counter recoil.

A suppressor also cools the hot gases coming out of the barrel enough that most of the lead laced vapor that leaves the barrel condenses inside the suppressor, reducing the amount of lead that might be inhaled by the shooter and others around them. However, this might be offset by increased back pressure which results in hot gas blowing back into a shooter's face.

Regulation

Legal regulation of suppressors varies widely around the world. In some nations, such as Finland, Norway and France, some or all types of suppressor are essentially unregulated and may be bought "over the counter" in retail stores or by mail-order as they are considered a great help, along with hearing protection, to preserve the hearing of the user and any onlookers. In these same countries, however, the firearms themselves are strictly (by US standards) controlled.

Asia and Oceania

In Hong Kong, "any accessory to such arms designed or adapted to diminish the noise or flash" is within the definition of 'arms' under the Firearms and Ammunition Ordinance (HK Laws. Chap 238). As such, a permit is required (as with firearms and ammunition) for possession which would otherwise be illegal and carries penalties up to a fine of HK$100,000 and 14 years in jail.

New Zealand does not require permits for the manufacture, sale, possession, or use of a suppressor.

In Turkey, civilian purchase, sale or possession of suppressors are strictly prohibited, with possible jail terms of up to 25 years for if convicted. Suppressors can only be purchased by military personnel when approved by the officer in charge of the base armory. Individual law enforcement officers are not eligible to purchase or possess suppressors unless these are issued by a local agency, in which case these would be registered to the General Directorate of Security in Ankara.

Europe

In Austria, the purchase or possession of a suppressor is prohibited according to §17 of the Austrian Weapons Law.

In Norway, silencers can be bought without any permits or registration.

In Denmark, the Danish Weapons And Explosives Law makes the unlicensed possession of a suppressor illegal. A permit may be acquired from the local police, but permission is almost always denied. Only police and hunters with special permission for the emergency slaughtering of livestock inside buildings are allowed to use them.

Italy prohibits the purchase or possession of a suppressor except for military personnel.

In Sweden, suppressors for specified calibers are legal for hunting purposes. A license is required, but is normally always granted.

In Finland, suppressors are not classified as "weapon parts". Therefore, they are completely legal in all calibers, requiring no registration or permit. As a somewhat generalized rule of thumb, Finnish gun law classifies only parts subject to firing pressure directly involved with firing the cartridge as weapon parts; barrels, bolts, and any part with a chamber. These are restricted to owners with a valid permit. All other parts and accessories are not weapon parts under this classification. This would include parts like magazines, various sights and scopes, and also suppressors.

In Poland, suppressors are not classified as "important weapon parts". Therefore, they are completely legal in all calibers, requiring no registration or permit. However using suppressors (even installing) with firearm is prohibited. Only police and military are allowed to use them.

In the United Kingdom, sales of suppressors fall into four categories of use. For replica and air weapons, the purchase of a suppressor requires no license and in most cases, no identification requirement. For shotguns, these will probably require the presentation of the buyer's shotgun certificate but will not be recorded. For a small- or full-bore rifle, the firearm certificate (FAC) will need to show permission for the purchase of a suppressor and also the gun for which it is intended. All firearms certificates have the firearm and caliber approved by the police and annotated to the document before a suppressor may be purchased. Police forces usually approve applications for a suppressor for hunting and target shooters, as the risks of litigation for personal injury, especially high-tone deafness resulting from shooting-induced hearing loss, are significant; and noise pollution in general is a problem for shooting sports.

North America

In Canada, a device to muffle or stop the sound of a firearm is a "prohibited device" under the Criminal Code. A prohibited device is not inherently illegal in Canada but it does require an uncommon and very specific prohibited device license for its possession, use, and transport. Suppressors cannot be imported into the country.

The United States taxes and strictly regulates the manufacture and sale of suppressors under the National Firearms Act. They are legal for individuals to possess and use for lawful purposes in thirty-eight of the fifty states. However, a prospective user must go through an application process administered by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), which requires a Federal tax payment of USD 200.00 and a thorough criminal background check. The USD 200.00 buys a tax stamp, which is the legal document allowing possession of a silencer. The market for used suppressors in the U.S. is consequently very poor, which has driven innovations in the field (buyers want the height of technology, because they are basically "stuck" with the purchase). Primitive suppressors are available in other countries for under USD 40, but they are usually of crude construction, using cheap materials and baffle designs that were obsolete in the United States by the 1970s. While suppressors in the US are more expensive (hundreds to thousands of dollars), they are generally built with highly advanced baffle stacks and exotic materials like Inconel and high-grade heat-treated stainless steels. Several states and municipalities explicitly ban any civilian possession of suppressors.

The Federal legal requirements to manufacture a suppressor in the United States are enumerated in Title 26, Chapter 53 of the United States Code. The individual states and several municipalities also have their specific requirements.

Naming

Many users prefer the term "suppressor" to "silencer", as no firearm suppressor is truly silent. Others believe that "suppressor" is more politically correct, and does not carry the same "hitmen and mobsters" stigma that the general public has applied to "silencers".

UK police forces use the term suppressor while the United States Department of Justice, Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) refers to these devices as "silencers".Functionally, a suppressor is not meant to completely silence a firearm, but to make its sound unrecognizable. Even subsonic bullets make distinct sounds by their passage through the air and striking targets, and supersonic bullets produce a small sonic boom, resulting in a "ballistic crack". In addition, the sounds may reflect off adjacent structures or terrain. Semi- and fully-automatic firearms also make distinct noises as their actions cycle, ejecting the fired cartridge case and loading a new round.

The ideal suppressed weapon would therefore be either a single-shot or a manually-operated repeating firearm such as a bolt action rifle (see Firearm types above). Effective suppressors either use a large total suppressor volume, or a moderately large volume plus many baffles, or wipes. It is possible to design a very small and compact suppressor with wipes which effectively silences a pistol; these suppressors have a lifetime of as few as five shots and typically no more than a few magazines of ammunition. Most suppressor designs trade reduced total volume and weight for somewhat louder noise, which is still tactically useful. The optimum point for any particular design depends on the suppressor's intended use.

See also

• OTs-38 Stechkin silent revolver
• Sound Blimp

References

External links

• Howstuffworks article - How does a gun silencer work?
• legal GunTrustlawyer.com Silencer legality - Legality and ownership of silencers for each state