Suppressor
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. It generally takes the form of a
cylindrically-shaped
metallic tube that is fitted into the barrel of the firearm, with various internal mechanisms to reduce the sound of firing by manipulating the escaping
propellant gas, and sometimes by reducing the velocity of the
bullet.
The
internal combustion engine muffler or silencer was developed in parallel with the firearm suppressor, and applies many of the same techniques to engine
exhaust to provide quieter running engines.
Most suppressors work by allowing the pressurized
gases in the barrel to slowly expand before they exit the muzzle of the firearm, resulting in a "phum" sound rather than a bang. The process is comparable to slowly opening a soda can and hearing a hissing sound rather than a "pop". Some suppressors are also structured like
motorcycle mufflers for the sound waves to cancel as they reflect from the sides of the casing. Such suppressors are inherently more difficult to design and to manufacture since they require more precise cutting and assembly. For this reason, they are often bigger and are mounted on large-caliber rifles where the added sound suppression is needed most.
Motion pictures have produced the common misconception that sound suppressors ("silencers") completely silence the weapon's sound, which is in most cases very far from the truth.When mounted on pistols and
submachine guns with subsonic ammunition, a good suppressor can reduce the sound to a loud pneumatic clacking noise, roughly comparable to a stapler gun. Only on very small-calibre weapons, such as
.22 LR calibre ones, can the weapon's report truly be silenced. On rifles, the noise reduction is large but the sound is generally still loud enough to be heard hundreds of meters. The noise reduction is still often large enough to allow safe shooting without hearing protection. Another important factor in sound signature suppression is the muzzle velocity of the ammunition. In rifles, the supersonic bullet itself produces a noticeable crackling sound as it travels through the surrounding air. For this reason, it is more difficult to lower the sound signature of these firearms effectively. Subsonic ammunition reduces sound report, but has a lower velocity than supersonic ammunition and is thus less lethal and has a shorter range.
One solution is to lower the muzzle velocity of the cartridge. Some suppressor designs do this by allowing gas to bleed out of the barrel before the bullet exits; others do it with rubber "wipes" that use friction to slow the bullet. While this method is effective, it dramatically reduces the range, accuracy, and stopping power of the projectile. The wipes generally wear out and lose effectiveness after relatively few shots.
Most suppressors can be removed by unscrewing them off the barrel, but others, such as suppressors that bleed off powder gasses to reduce the ammunition velocity, are built into the barrel and can only be removed by removing the barrel. Integral suppressors are also more robust than detachable suppressors, because they attach to the barrel over much of the barrel's length, making them less susceptible to bending if subjected to torque, such as when the firearm is dropped. A detachable suppressor that is even slightly misaligned may come into contact with the bullet, significantly degrading the accuracy at best, and at worst resulting in the suppressor being ripped off the firearm when used.
Suppressors have other benefits besides reducing noise. A suppressor changes the sound report of a shot fired, spreading the sound and making the shooter harder to pinpoint. Most suppressors are effective recoil reducers. A suppressor also cools the hot gasses coming out of the barrel enough that most of the lead 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. In close quarters, a suppressor reduces a fired round's shockwave-like pressure effect on the shooter, hindering dizziness and disorientation.
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Diagram from Maxim's 1908 silencer patent 916,885 |
Early suppressors were created around the beginning of the 20th century by a number of inventors. inventor
Hiram Percy Maxim is credited with inventing and selling the first commercially successful models circa 1902. Maxim called his device the trademarked name
Maxim Silencer. Later this style device would be widely adapted to
internal combustion engines to generate the muffler, still called a
silencer in the UK. 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, in newsprint and in non-technical usage favors the technically inaccurate, but historically first term that was used,
silencer.
The suppressor was first introduced into the
United States Army Air Forces before
World War II.
Office of Strategic Services agents during World War II favored the newly-designed
High Standard HD .22 caliber pistol. The addition of a sound suppressor baffle to the barrel absorbed 90% of the noise.
William Joseph Donovan, Director of the OSS, demonstrated the pistol for
President Roosevelt while visiting the
White House. Donovan fired ten shots into a sandbag without interrupting the President as he dictated a letter.
Legal regulation of suppressors varies widely around the world. In some nations, such as
Finland and
Norway, some or all types of suppressor are practically 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. Interestingly, in many such countries the firearms themselves are strictly controlled. Other nations, such as
Canada, practically forbid their private citizens from owning suppressors, while yet others, such as the
USA, heavily tax and strictly regulate their manufacture and sale.
In the
United States, it is legal in most states for an individual to possess and use a suppressor that often can be manufactured for less than $10; however, one must go through the
National Firearms Act process administered by the
BATFE. Such transfers also require a federal tax payment of two hundred and a thorough
background check. Some states, however, explicitly ban any civilian possession of suppressors.
In the
United Kingdom, the sale of "sound moderators" is unregulated, however attatching it to a rifle is considered breaking the law. As such, persons in posession of rifles must apply for a separate slot on their Firearms Certificate for a sound moderator.
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
World War II.
The suppressor is typically a hollow 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 reference to old-fashioned collapsing
telescopes). The outer casing of the suppressor is typically referred to as the
can.
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. The trapped gas can cool and expand, reducing the pressure and velocity as it exits the suppressor. The divisions between these chambers are called baffles or wipes (see below). There are typically at least 4 and up to perhaps 15 chambers in a suppressor, depending on intended use and design details. The engineering design of modern suppressors is analogous mathematically to the design of electrical filters, and many of the same design techniques may be used to design either.
Often, a single, larger
expansion chamber is right at the barrel's muzzle, which allows the propellant gas to expand considerably and slow down before most of it begins to encounter the shaped baffles or wipes section of the suppressor.
Suppressors vary greatly in size and efficiency. One disposable type developed in the 1980s by the US Navy for 9 mm pistols is 150 x 45 mm (5.9 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 350 mm (13.78 in) long and 75 mm (2.95 in) in diameter and will work effectively for hundreds of shots with standard ammunition.
Baffles
Baffles are inner walls which separate chambers and are designed not to touch the bullet as it passes the baffle, typically by having a circular hole at least 0.05 inch / 1 mm larger than the bullet caliber. Baffles are typically metal, either machined solid shapes or stamped sheet metal. A few suppressors for small calibers (such as
.22 LR) have successfully used plastic baffles.
Baffles are separated by
spacers, which keep them aligned at the intended distance apart inside the suppressor can. Some baffles are manufactured in one piece with their spacers being part of the baffle.
Modern baffles are usually carefully shaped to divert the gun 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 slanted surfaces, angled to one side, then the other, back to the first side, and so on through the stack of baffles.
Some suppressors use a single, helical baffle which winds around the bullet hole in a single piece throughout the baffle length.
Baffle lifetime
Baffles usually last for a significant number of firings. They are heated and slightly eroded by the gun's propellant gas rushing past them, and over time erosion will damage the suppressor. Damage happens slowly with steel baffles and slow single shot firing, happens rapidly with steel baffles and fully automatic firing, and happens extremely rapidly with aluminum baffles and rapid fire. Some modern suppressors having steel baffles can be fired for extended periods of time on fully automatic without damage, and other modern suppressors use high temperature alloys such as
inconel or
titanium for longer life and reliable service with automatic fire. The highest quality rifle suppressors available today have a service life of greater than 30,000 rounds.
Wipes
Wipes are inner dividers intended to touch the bullet as it passes. Wipes are typically rubber or plastic or foam. They may have a hole drilled in them before use, or a pattern cut through at the point the bullet will strike them, or they may simply use the bullet's energy to punch a hole.
Wipes typically last for a small number of firings, perhaps no more than 5 before their performance is significantly degraded.
Liners
Various materials may be used to line the chambers and dissipate or cool the gases; these include metal mesh and steel wool. These are more effective than empty chambers, but less effective than wet designs (see below). Steel wool degrades very rapidly (ten shots or so); metal mesh may last for hundreds or thousands of shots of semi-automatic fire, or somewhat less for fully automatic fire.
Suppressors and Silencers
No suppressor can completely eliminate the sound of firing a firearm. Even subsonic bullets make distinct audible sounds simply flying through the air and hitting targets, and supersonic bullets produce a sonic boom shock wave as well with a much louder crack. Semi-automatic firearms also make a distinct noise as their action cycles, ejecting the old empty cartridge and loading a new one.
Some suppressors do an extremely effective job of quieting the muzzle blast sound from firing, to the point that the action and bullet sounds are as loud or louder than the muzzle blast escaping the suppressor. These are often inaccurately referred to as silencers; however they do not completely silence the shot's other sounds.
Very effective suppressors either take large total suppressor volume, 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 4-5 shots and typically no more than a few magazines of ammunition. Larger wipeless (baffle only) pistol or rifle suppressors may be nearly as effective for long lifetimes (hundreds or thousands of shots) but are relatively bulky, clumsy, and heavy.
Most suppressors designs trade reduced total volume and weight for somewhat louder noise, which is still significantly tactically useful. The optimum point for any particular design depends on the suppressor's intended usage.
Wet suppressors
Some suppressors, 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 suppressor. 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 (and least preferable, as well), as it leaks while being as messy as grease, leaving behind a fine mist of condensed oil after each shot.
Advanced types
In addition to attempting to initially contain and slowly release the pressure associated with muzzle blast or reducing pressure through the use of coolant mediums, the properties of the sound waves generated by the muzzle blast are considered and dealt with in advanced suppressor designs. In these designs, effects known as frequency shifting and
phase cancellation are used to make the suppressor quieter. These effects are achieved by separating the flow of gases and causing them to collide with each other again.
The intended effect of frequency shifting is to shift audible sound waves freqencies 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, cancelling the amplitude of the wave and so eliminating the pressure variations perceived as sound. However, because muzzle blast creates
broadband noise rather than
pure tones, complete phase cancellation is very difficult to achieve, though any degree of
destructive interference may be considered beneficial.
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 a fixed baffle design, or an adjustable baffle design.
These design concepts have been used successfully but are still relatively rare in common suppressor designs.
Improvised
It is widely believed that suppressors can be improvised with any baffling material. Such attempts are only marginally useful, have a very short lifespan even if effective, and are often dangerous to the user. In areas where suppressors are regulated, such improvised suppressors are usually illegal regardless of whether they actually reduce the sound of a firearm. Even suppressors intended for paintball guns, while providing no functionality for firearms, are illegal in the United States. Nonfunctioning or dummy silencers are available for replica enthusiasts and are generally legal in most states in the United States.
The overwhelming majority of improvised suppressors popularized by movies and television (plastic bottles stuffed with insulation, potatoes, pillows, etc) do nothing to dampen a gun blast.
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". For any further increase in velocity higher than 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
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.
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 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·lbs (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.
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Line drawing of De Lisle carbine, A .45 ACP carbine fitted with a very effective suppressor |
The type of gun also affects 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 is not as easy as just threading the barrel and screwing one on. Most semiautomatic pistols in larger calibers,
9 x 19 mm Luger 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 attaching a suppressor 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
John Browning designed tilting barrel lockup, as used in the
M1911. 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. 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, but perhaps also efficiency.
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. The small powder charges of the .22 Long Rifle keeps suppressors small; many, like those available for the
Ruger 10/22, are no larger than a heavy barrel.
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The MP5SD5 (with integral suppressor) being fired |
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. The
.45 ACP is an excellent choice, since the standard 230 grain (15 g) 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 (see above).
While suppressors are most effective 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 muzzle blast sound location. 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 increase the difficulty of location from the area of the target.
Due to their associations with organized crime and intelligence operatives, suppressors are commonly encountered in fiction. In addition to traditional suppressors, such as the ones used by
John Clark in
Tom Clancy's
Without Remorse, or by many characters in
James Bond books and movies, mention is often made of improvised suppressors. In
Chuck Palahniuk's
Fight Club, Tyler Durden describes a dubious method to silence a gun by drilling holes in it. Various fictions, like the recent film
Lady Killers, and the 1998 film portraying the life of Irish criminal Martin Cahill a.k.a "The General", mention the use of a regular
pillow for noise suppression, a technique also used by the character Dina Araz in the TV-series
24. In
Lawrence Block's
short story collection
Hit Man, the main character wraps
insulation material around a pistol's barrel as a makeshift suppressor. According to the novel
Hannibal a soda bottle taped to the muzzle of the gun will reduce the sound of the report. In the game
Postal 2, the player can use a live
Cat as a silencer on their weapon. None of these methods are effective in real life. Suppressors in fiction often completely silence even powerful rifles or change the sound to resemble a "pew-pew" noise, which is wholly inaccurate.
*
Flash suppressor*
Howstuffworks article*
Bowers, US suppressor manufacturer
*
Advanced Armament Company*
Ase Utra, Finnish suppressor manufacturing
*
Gemtech Military & Civilian U.S. Suppressor manufacturer
*
Husssh Innovative suppressor design from New Zealand
*
Image of a suppressor for the
Heckler & Koch submachine guns
*
Maxim Silencers, a company making industrial sound suppression devices for engines, compressors, and other applications under the Maxim name.
* Paulson,
Silencer History and Performance, Vol 1: Sporting And Tactical Silencers, ISBN 0873649095
* Kokalis, Parker, and Paulson,
Silencer History and Performance, Vol 2: Cqb, Assault Rifle, and Sniper Technology, ISBN 1581603231
* Parker,
Firearm Supressor Patents: Vol. 1 United States Patents, ISBN 1581604602
