An Introduction to Weapon suppressors and silencers.

Ben Broughton via google ^ | 2000 | 2000 Ben Broughton

[vannrox]

Suppression

Ah, suppressors and silencers. We Shadowrun players have all had a sneaky character or NPC whack a few people every once in a while. Using a suppressed firearm is a prime method of doing so. But if you've watched as many movies as I have, you may have a few misconceptions about suppression, or you may just be interested in how it works. That's what this file is all about.

If you would like to see simple rules and explanations for suppression, please visit the rules section of this site. If you want more details, keep reading...

The Intention of Suppression

First off, I'd like to clear up a little nit-pick of mine. There is no such thing as a "silencer". By definition, no firearm can be truly silenced; there will always be some sound associated with the discharge of a firearm. Therefore, use of the term "silencer" in context with firearms is a misnomer. The correct term is "suppressor" or "sound suppressor."

The intention of any suppressor on any firearm is to dampen the overall noise of the weapon being fired and make it harder to determine the origin of that sound. Some cartridge/suppressor combinations are so effective that you would associate the sound they make more with a stapler stapling a few pieces of paper together rather than a firearm being discharged.

An important parameter to understand when dealing with firearm suppression is the speed of sound in air. This can be between 1,080 and 1,120 feet-per-second (330 to 342 m/s) depending on local temperature, humidity and atmospheric pressure levels. Keep that in mind. We'll get to the implementation of that parameter in a second...

Which sounds are bad?

Any sound that seems to advertise that you're firing a gun! There are basically three types of noise that need to be considered in order to suppress a given weapon.

The first and loudest is muzzle blast. Muzzle blast is caused by the high pressure gases used to propel the bullet suddenly escaping into the atmosphere as the bullet exits the muzzle. Every type of suppressor works to reduce this pressure by increasing the volume that the gases are allowed to expand in, reducing the gas temperature (cooling), delaying gas exit through trapping and turbulence, or any combination of these methods.

The second is the shock wave created by a bullet in supersonic flight. When any object reaches the speed of sound in air, air molecules can no longer move out of the way of that object. Sound waves created by the bullet in flight build up upon each other, creating a shock wave. The pressure these waves create is eventually released, creating noise. The sound of an object the size of a bullet flying in excess of the speed of sound is usually not as loud as the muzzle blast, but is represented by a sharp "crack" similar to that of a bullwhip near the muzzle, or a tearing sound if there are surfaces for the sound to reflect off of along the bullet's flight path. It is extremely difficult for the human ear to determine a point of origin from this sound. In open areas or at longer ranges, it is nearly impossible.

In any case, the less sound there is, the better. For this reason, it is a desirable feature for a suppressed weapon to fire bullets that do not exceed the speed of sound.

The third is the sound of the weapon itself. On its own, the sound of the hammer or striker being released causing the firing pin to strike the primer cap of the cartridge is represented by a "click" sound, almost identical to that of a firearm being dry-fired. Louder still is the sound of an automatic weapon cycling ammunition. This is also a relatively quiet sound, but it may be necessary to keep those sounds from happening, if proximity is an issue. Some weapons have the ability to lock the bolt or slide closed, effectively neutralizing that sound. In that case, manually cycling the weapon is required to fire subsequent shots. As with a bolt-action rifle, for instance.

How does a suppressor work?

Have you ever heard a car without a muffler? The reason it was so much louder was because the expanding gases from the exhaust were escaping the tailpipe at velocities beyond the speed of sound. The gases were creating a supersonic shock wave while exiting the exhaust pipe. The main thing a suppressor is designed to do is to slow the escape of propellant gases, just like a muffler.

There are a lot of different suppressor designs out there. Some more efficient than others. But generally, there are two types of suppressors and a common mechanical process for each of them.

A basic type of Muzzle Suppressor.

The most common and oldest historically is the muzzle suppressor. Muzzle suppressors are usually detachable, and consist of a relatively large volume chamber at the rear of the suppressor just ahead of the muzzle which allows gases to expand quickly, followed by a series of baffles with a hole in the middle, through which the bullet passes. These baffles slow the forward motion of the expanding propellant gases, trapping them inside of the suppressor. This type of suppressor does nothing to slow the bullet itself. Therefore, if supersonic ammunition is used, a sonic "crack" can be heard as the bullet exits the muzzle.

The other type of suppressor is the barrel suppressor, or integral suppressor. This type of suppressor is built around the barrel of a firearm and incorporates characteristics of the muzzle suppressor, along with another feature: the barrel is modified for velocity control. This includes a series of perforations or ports in the barrel which are used to bleed some of the expanding propellant gases from behind the bullet, in order to slow it to subsonic speeds. Barrel suppressors are an integral component of a weapon, and are designed for use with marginally supersonic ammunition. (Such as the 9mm Parabellum or .22 Long Rifle cartridges.) Perhaps one of the most widely known weapons to have a suppressor integral to its design is the Heckler & Koch MP5SD submachine gun.

A common technique used to aid sound suppression in both types of suppressors is the use of "wet technology". This consists of a suppressor made of a corrosion-resistant material (usually stainless steel) which, in addition to the features mentioned above, houses no more that a few cubic centimeters of water. The introduction of water to the system helps to reduce gas temperature and volume quicker. This technique can help reduce sound pressure levels by as much as 10dB, but does add a bit more weight to the weapon.

Which cartridges can be suppressed?

The answer is all of them. But as you might have guessed by now, some cartridges can be suppressed much easier and/or to a greater degree than others. To be more precise, when suppressed, some cartridges will retain ballistics closer to their original design specifications. I'll use two common handgun cartridges as a quick example: The .45 ACP, which is an inherently subsonic cartridge, and the 9mm Parabellum, which has a terminal velocity just above supersonic speeds in its standard loading.

Because the .45 ACP fires its bullet at subsonic velocities (855 fps for the US M1911 Ball load), there is no supersonic shock wave created during flight. Therefore, it is a relatively simple task to suppress the round when fired; only propellant gases need to be contained. Very little velocity and kinetic energy are lost in the process. Range is also not effected substantially.

The 9mm Parabellum (at 1150 fps), however, needs to be slowed to subsonic velocities or else the "crack" of air pressure rapidly decompressing behind the bullet will be audible. This can be accomplished in two ways:

1) The suppressor can be designed to bleed the excess propellant gases before the bullet reaches the muzzle of the weapon, in effect slowing the bullet to below supersonic speeds before it exits the muzzle. (See integral suppressors, above.)

2) The cartridge can be "cold-loaded", meaning less powder than normal is added in order to keep the bullet from achieving supersonic speeds. In this case, a heavier than normal bullet is usually used as well to help keep velocity low and striking energy high. (A muzzle suppressor can be used to great efficiency with any subsonic load.)

In either of these cases, the 9mm Parabellum's ballistics will be adversely effected, decreasing energy and range slightly.

Rifles and Suppression

Some cartridges aren't designed to be suppressed. All conventional rifle cartridges fall into this category, as well as some of the more powerful handgun cartridges. But unlike handgun cartridges, rifle cartridges are designed to send a bullet very long distances. For instance, according to the United States Marine Corps, the effective range of a 9mm Parabellum from an MP5 is about 100 meters. The 5.56x45mm NATO cartridge fired from an M16A2 is designed to be point-target effective at more than 500 meters.

Rifle cartridges accomplish this by packing a relatively large amount of powder behind a relatively light, aerodynamically efficient bullet. When it comes to suppressing a rifle cartridge, the problem is twofold:

1) Velocity. A bullet is usually designed to exit a rifle's muzzle at a velocity of two to four times the speed of sound, depending on the cartridge. This will obviously create a supersonic shock wave which will be audible and so limits our ability to suppress the weapon.

2) Suppressor size. The relatively large amount of powder being converted into propellant gases requires an equally large suppressor to contain them in order to keep the shot from making much noise.

With these two factors in mind, you can see that it is largely an impractical endeavor to fully suppress a rifle cartridge.

But what about the "cold-loading" I was talking about earlier? Well, that is a possibility, but one that's not as easy to accomplish with a rifle cartridge as with a handgun cartridge.

Rifle cartridges like the 5.56x45mm NATO produce most of their ballistic performance through the use of a very high velocity. (Almost three times the speed of sound. Remember, M/2*V²=KE.) "Cold-loading" a rifle cartridge to subsonic velocity would severely hamstring its performance, causing it to lose a very substantial amount of range and energy in the process.

Also, due to the larger powder capacity of their cases, rifle cartridges are particularly sensitive to the amount of powder used to propel the bullet downrange. "Cold-loading" rifle ammunition far below design specs will, in many cases, create very inconsistent ballistics from shot to shot. Therefore, it is not a practice many are in the habit of. However, there are two other ways to deal with this problem.

The first is to do what Knight's Armament Company did while designing a detachable suppressor for the SOPMOD M4A1 used by US Special Forces. They decided that full suppression wasn't needed. They designed a suppressor which reduces sound and flash signature as much as possible, but does not attempt to contain it wholly. Bullets fired from the SOPMOD M4A1 still travel from the weapon at beyond the speed of sound and the weapon still makes a significant amount of noise when fired. But not nearly as much as it does without the suppressor.

In close quarters, where the reverberation of loud sounds can cause pressure variations which can be disorienting, not to mention cause temporary or permanent hearing loss, this rather limited reduction in sound pressure can make a significant difference in the operator's performance. Therefore, it's beneficial to have this limited suppression available.

The second option - one that is becoming more and more popular due to the practicality of it - is to use specialized rifle cartridges that remedy the issues created by "cold-loading" rifle cartridges. These specialized rifle cartridges (called "Whisper" cartridges by their inventor, J.D. Jones) fire heavy, ballistically efficient rifle bullets at subsonic velocities from a case with a powder capacity comparable to that of some pistol cartridges, solving the rifle case "cold-loading" problem. Essentially, what happens is that the bullet loses energy from wind resistance much slower than a pistol bullet would, attributing to better range and striking power, while ballistics are held to match-grade accuracy and round-to-round consistency. Even with a bit more arc in the trajectory and flight time limbo, these cartridges do have the longest range of any subsonic cartridge developed thusfar.

You can read more about rifles and sound suppression by clicking here.

Side Effects of Suppression

1) Altered zero. Any weapon with a suppressor attached will have a substantially different zero (point of impact) from when the suppressor is not attached. Luckily, the suppressed zero is usually repeatable. This cannot be avoided. Tandem aiming devices or a device which can calculate two points of impact will be necessary if the weapon is to be used both with and without the suppressor attached.

2) Higher cyclic rate. Any automatic weapon with a suppressor attached will have an increased rate of fire, due to the fact that a suppressor is designed to contain propellant gases, therefore, pressure is held within the system longer. This has the effect of increasing pressure within the weapon's operating system, so increasing ROF. Some types of operation (particularly blowback operations) are more sensitive to this effect than others.

3) Increased heat retention. Because a suppressor contains propellant gases, it also contains and absorbs heat. As a consequence, barrel heat dissipation happens at a slower rate. In conjunction with side effect #2, these effects translate to increased barrel wear.

4) Increased fouling. Suppressed weapons need to be cleaned more often due to the fact some of the propellant sedement is forced back into the weapon's action by the suppressor.

Suppressor Maintenance

After a certain amount of usage, all suppressors get fouled by propellant gas sediment. Most modern suppressors are easily maintained by a complete or partial submersion in a liquid solvent designed to break up fouling. This should be done after each use. Other cheaply designed suppressors (such as some designed for the Russian PSM pistol) are actually disposable.

Also, water is a byproduct of gunpowder combustion. Because a suppressor is designed to contain this combustion, water tends to accumulate inside the exapansion chamber of a suppressor. For this reason, most modern suppressors are coated inside and out with a corrosion-resistant finish. An effort should be made to remove all water from the suppressor unit after each use.

I've heard a few people talking about "blowing out" a suppressor. Basically, the only way something like this could happen with a modern design is if the suppressor were seriously neglected or maliciously tampered with. I personally have never heard of this happening to a well-designed suppressor. The term "blowing out" suggests that the suppressor has failed to contain the pressure created by the expanding propellant gases inside of it and has literally exploded. While very unlikely, this could happen for a number of reasons, the most likely being some kind of obstruction in the bullet's path.

Please see rules for suppression.

© 2000 Ben Broughton

[Octar]

Bump

[MadRobotArtist]

The internal combustion engine makes noise because each cylinder houses a small explosion which drives the cylinders down, which in turn powers the car, and makes it go. The exhaust you hear are those little explosions. The tailpipe, and muffler keep it quiet. It has nothing to do with velocity or any of that.

[MadRobotArtist]

My wife is a gaming geek, and we actually have this book. The majority of the stuff in it is crapola, but you can find some nuggets of truth in it.

[AAABEST]

When I was stationed at Ft. Benning, we did a lot of range duty. Many days in a pit changing targets.

Good training to be on the receiving end of weapons fire.

[elmer fudd]

The supersonic crack of bullets overhead is loud, as loud as a child's cap pistol. Also, you hear it before you hear the sound of the muzzle blast.

Suppressors and sonic booms are an interesting subject. You hear a sonic boom relative to what it passes, not from where the bullet came from. Basically you'll hear it crack when it passes you, and you'll hear the echo of it's boom as it passes other objects. You still hear a gunshot, but it doesn't sound like a gunshot and you can't pinpoint it's origin. Silencers are also much more effective outdoors than they are inside. I'm not exactly sure why that is, but it's true.

[elmer fudd]

I fooled around once shooting arrows out of a double barrel shotgun. I'd only use a little powder and I used two wads, one in the cartridge and one at the base of the arrow immediately after the chamber. When you got the powder charge just right you could launch the arrows at about 500 fps and in almost total silence. I probably could have perfected it if I had had reloading equipment. As it was though I was measuring my powder charge with an old .22 casing and cutting open shotgun shells with a carpet knife and it was hit or miss. Sometimes the arrow would barely make it out of the barrel and other times it sounded like a .45.

[Squantos]

There used to be a barrel one could buy that fit a ruger 10-22 and Model 77/22 that allowed a standard easton aluminum arrow without the fletching to be fired in total silence using a small .22 blank like the ones used in the power drivers/hammers. It had a small barrel within a barrel....was real quiet

I have looked for one of those but they seem to have quit making em.

Stay Safe and thanks for the info.......

[Joe 6-pack]

"You ain't been corking off that M256 in a residential area again, have you, Joe? ;-)"

What? who? Me? Naaaah....

[xm177e2]

The supersonic crack of bullets overhead is loud, as loud as a child's cap pistol.

Also, you hear it before you hear the sound of the muzzle blast.

Can you still tell the direction it came from, or is that much more difficult when the weapon is suppressed?

[HP8753]

Or you can just use some CB's... .22 ammo made for indor shooting by CCI.
750ft /sec w/ 29 grain bullet.

The CB's used with a bolt action rifle are quieter than my pellet gun.And you can see the bullet going down range.Packs more punch than my pellet gun does also.

CCI CB AMMO

[2nd_Amendment_Defender]

Why is it we are only good enough citizens to own suppressors if you pay a 200 dollar tax.

When did these regulations start by the B.A.T.F. ?

[ctdonath2]

1934, with the National Firearms Act (NFA). All downhill from there.

[sit-rep]

bttt

[spunkets]

" a car without a muffler?"The velocity of sound in air is about 1125ft/sec. The velocity of the gases exiting a gun following the bullet is ~3000 ft/sec. Whether it's black, or smokeless powder that velocity doesn't change much and can be used to calc. recoil from conservation of momentum.

In an IC engine the cam opens during the power stroke. ~7-15in into the pipe, depending on the cam, the the flame temp is about the same as a rifle shot. If the pipes are ~20in, as on a dragster yellow flames fly out, the sound is definetely supersonic at ~<3000ft/sec. Otherwise with full pipes, it then decreases rapidly as it goes through the pipe.

Headers and the stock cast manifolds are setup so there's a reverberation in the tubes so the momentum of the exit gases leaves a lower than atmospheric pressure in the cylinder. That condition then exists when the intake valve opens. That causes a higher velocity during cylinder filling. There's some overlap in valve opening, so intake mix is going out the exhaust pipe. The exhaust pulse spreads backward quickly and shoves what mix is in the exhaust pipe back in the cylinder before the exahust valve closes. That backward pulse is quite a bit lower temp and corresponds to the slowing wavefront. The longer the pipe the slower it goes at the exit.

At any rate, if the sound has a definite crack w/o a muffler and sounds more like an airplane engine, it's supersonic. If it's a booming rumble it's subsonic.

[boris]

"the sound is definetely supersonic at the ~<3000ft/sec.

I don't know what you meant to say, but what you did say is nonsense.

--Boris

[boris]

Sorry, a spurious "the" crept into the quote.

Still nonsense without the "the".

[spunkets]

What I meant is the wavefront is at 3000ft/sec. The speed of sound is ~1100ft/sec.

[Gil Lindsey]

Great read. I would also stress the importance of the cleaning ritual with respect to matter forced back into the chamber due to backpressure from the suppressor, I own a semi-auto Ruger Mk.II with a Hammerli barrel liner and a Bentz chamber. This piece is very prone to extraction and ejection problems possibly because of the tight chamber, if not kept spotless (as all firearms should be kept!). However, with a VERY EFFICIENT integral suppressor, the debris is forced back into the chamber,evidently as the pressure curve drops off, as I realize no "breech pop". The same level of efficiency in a suppressed bolt action action rifle with a "factory" chamber does not seem to need as much attention. Needless to say, both require cleaning after a long day at the range, but the semi is more demanding. A solution I use is 90% Kroil and 10% G.M. Top End engine cleaner. After I remove the bolt with the "speed strip" conversion, I use a soft rubber plug in the muzzle of the suppressor, suspend it vertically, muzzle down, and fill the integral unit to the chamber. It loosens the crud, and I clean the lower unit as usual. The "speed strip" kits makes all of this a short task. I think we all would agree that extreme accuracy and reliability comes with a price, but with suppressed weapons the cleaning cycles can be very short. I feel the trade off is worth it. I also use lithium grease as an ablative material in the rear chamber, though the integral unit is extremely impressive without it (110-113db) because the manufacturer emphasized the benefit of a grease getting into all of the nooks and crannies sometimes occupied by moisture and corrosive elements. I will be happy to share with you the manufacturers of my units, as I have seen many, yet none finer. E-mail me and I'll give you the addresses.
Gil
gillindsey@hotmail.com