How do gun silencers work?

Nice explanation of silencers. There is one more thing to add, however. TV and the movies often show people using revolvers with silencers and the sound is equally as quiet as when silencers are used with automatic pistols. Revolvers will never be as quiet as automatics because of the gap (albeit very narrow) between the cylinder and the barrel. That gap will allow some of the gases to escape before the bullet reaches the silencer. Using a silencer with a revolver will result in a quieter shot than without but there will be more noise than results when using an automatic.

Thank you.

I’ll keep that in mind.


Looks like someone beat me to writing that one… BTW, is it up yet? I can’t see it!

Incidentally, there is one revolver than can be effectively silenced- the Nagant M1895.

Bricker’s report is How do gun silencers work? You get early notification if you subscribe to the email.

Silly, but related question - my understanding is that the ‘potato silencer’ is usually effective in it’s goal of reducing or disguising the sound of a pistol being fired, with of course an effect on accuracy and distance of the projectile. Is this an accurate summary?

I believe that a Dan Wesson revolver with its barrel tightly screwed down to virtually eliminate its cylinder gap can be suppressed.

A few extensions to Bricker’s good but IMHO, slightly too brief Staff Report:

27CFR479.11 (warning: PDF) defines as a Class III (restricted) firearm “(g) a muffler or a silencer for any firearm whether or not such firearm is included within this definition.” As Bricker notes, such “firearms” are legal to purchase after filling out the necessary forms (ATF 4473) and paying for the tax stamp, state and local laws permitting.

Most handgun-caliber rounds have subsonic loadings which can generally be identified off the shelf by bullet weight; for the .45 ACP, it’s the 230 grain bullet, for the 9mmP it’s 147 grain bullet, for the .40 S&W, the 180 grain bullet is subsonic. Older rounds (.45 ACP, .38 S&W Spl.) are subsonic in all SAAMI pressure spec loadings, and many modern handgun rounds are only supersonic (.357 Magnum, .10mm Auto, .357 Sig, .400 Cor-Bon). With the advent of the .357 Magnum (which was essentially a lengthened and slightly thickened .38 Spl. case with higher pressure specs) the tendency was to go to lighter, faster bullets, which was accelerated with the adoption of high capacity 9mmP handguns as standard law enforcement duty weapons giving high “one shot stop” percentages in defensive shootings without undo overpenetration. However, the desire to use the 9mmP in suppressed submachineguns for tactical entry (more to protect the hearing of agents rather than to be stealthy), plus problems with underpenetration of light & fast rounds through sheet metal and windshields led to the development of subsonic rounds that expand reliably but offered better general penetration. The problem with such rounds, especially ones as small and high in sectional density as a 9mm bullet, is that they still don’t expand as reliably as lighter rounds, and therefore both have less of a stopping potential per shot and pose a threat to bystanders in the case of overpenetration due to underexpansion. The pendulum swung back to heavy rounds, and now again back to lighter rounds (.357 Sig). My personal preference is the lighter rounds which expand more reliably and have a generally less punishing recoil, but they are poorly suited for silencer use.

Virtually all centerfire rifle calibers are supersonic, and can’t readily be downloaded to subsonic levels. Using a silencer or suppressor on such a gun may muffle the report and muzzle flash sufficiently that it can’t be immediately localized, but as Bricker notes, it isn’t going to stop you from hearing the “crack” caused by the wavefront of the supersonic bullet. So, when you see some bad guy in a movie screwing a cylinder about the size of a 2D cell Maglite onto the end of his rifle, it’s just Hollywood bullshit. Real suppressors for .30 centerfire rifles are generally about the size of a couple of tennis ball cans end-to-end. In the United States, silencers are highly restricted or outright prohibited for most hunting purposes, in contrast to many parts of Europe, where they’re actually required to comply with noise abatement regulations.

Bricker mentions that the object of the silencer is to reduce the exit pressure, which is absolutely true, but another way to look at it that may be slightly more intuitive is that it slows the gases down, so that when they exit the silencer they’re moving at subsonic speed. Many older silencers used to have, in addition to or in place of baffles, a mesh of what was essentially steel wool (or occasionally some kind of fire-resistant fabric) and sometimes holes dotted around the circumference of the can to give additional routes for the gases to escape. The mesh would get compressed or burned with use, limiting the longevity of the silencer. All modern (within the last decade or so) silencers I’ve seen are strictly the baffle type, and many claim to be good for thousands or even tens of thousands of rounds. Some suppressers, called “wet”, used to use water or oil as part of the suppression mechanism. Obviously, these are only good for a limited number of shots before refurbishment. I think that these have largely disappeared from the market.

There are some firearm rounds that are designed to fire quietly without a suppressor, including at least one shotgun round. These are specialty items though, generally associated with espionage, and neither available to the general public nor terribly effective in comparison to unsuppressed rounds of similar caliber. I’m not clear on the legal status of such ammunition, but I think a reasonably restrictive interpretation of ATF regulations would regard each round as being a silencer, and thus requiring an individual tax stamp. So, no point in getting the high capacity magazine for those guns.

“Destructive interference” isn’t bullshit, necessarily, but making it work reliably would require extensive highly nonlinear computational fluid analysis, and very precise control over gas velocity and pressure to make the results reproducible. A silencer design would probably be restricted to a specific firearm, or at least highly dependent upon barrel length and the lockup time (before the breech is unlocked and the slide permitted to move) in order to function correctly. I strongly suspect that few silencer manufacturers have the skill or capacity to perform this kind of analysis, and simply play with the parameters of the design until they get something that sounds quiet. So at best, it’s marketing hype for emprical testing.

In movies you sometimes see characters using a variety of household implements as improvised silencers. (I won’t go into detail out of respect for SDMB guidelines for not discussing illegal activities, but you can use your imagination.) First of all, as with many firearm-related urban legands from the entertianment industry none of these methods would really be effective for anything larger than a .22LR, and second, putting anything on the barrel of your gun in an effort to reduce the muzzle report is, as previously noted, considered a Class III firearm and must be taxed as such. So don’t do this at home without getting your stamp and checking local regs. Or better yet, don’t do it at all. A pair of earmuffs are much cheaper than a tax stamp and probably more effective.

Potato silencers are ineffective and also ill-advised from both a safety and legal point of view. Don’t even bother trying this out.


Thanks. I searched for it, but I guess it doesn’t turn up in the search engine until its due date.

How about the sound-is what you hear in the movies (and like the Wilhelm Scream I suspect
they all use the same sound clip)-that “fhhtt” sound-what you would actually hear in real life?
Could someone fire off a silenced round (subsonic) that nobody in an adjacent room would
ever hear?

There’s also the 1-liter pop bottle seen on CSI and ye olde pillowe from classic Perry Mason days.
If those work, who needs a licenced silencer?

The sounds you hear on t.v. and in films isn’t terribly accurate. The noise from a good silencer sounds like kind of like a barking cough, or scraping a metal comb over a plate of steel combined with a popping sound. I’ve seen an silenced .22LR (owned, as I recall, by a Treasury agent) built off of a Ruger Mark II pistol that was quiet enough that distinctive sound of the action was considerably louder than the report, and I’ve seen 9mm handguns (Beretta, Browning Hi-Power) where you could definitely hear the action over the report, though it certainly wasn’t quiet enough not to be heard in the next room.

I’ve read anecdotes of integrally-silenced .22LR pistols (custom, or in the alleged case of Mossod agents, built off of a .22LR Beretta Model 21 Bobcat) with a locking action (making them essentially single shot guns with a manually cycled action) in which you can actually hear the firing pin hit the cartridge over the report, but have never personally witnessed such a thing. Similarly, there are eyewitness and forensic reports of single shot “zip” guns being pressed up against the target with the muzzle gases being entirely contained in the body of the target, presumably making little or no noise. This would risk having the pressure back up in the barrel, however, and possibly damage the firearm and/or your hand.

It’s interesting and/or amusing to note that most of the time when you see a silencer being used on t.v., the barrel is not threaded to accept a silencer. So basically the actor is picking up the prop silencer and spinning it around the muzzle (presumably there’s a dowel that goes inside the silencer and the bore to keep it from just falling off) to make it look like he’s threading it on. In the place I like to call “reality” a firearm typically has to have a threaded extension to accept a silencer, a detail Scorsese gets right in Goodfellas:
Henry Hill: (v.o.) I only bought the damn guns because he wanted them and now he didn’t want them.
Jimmy Conway: (Trying to screw a silencer onto an unthreaded barrel) What the fuck are these? None of them fit. What’s the matter with you? What, do you want me to pay for this shit? I’m not paying for it!
Henry Hill: (v.o.) I didn’t say a thing. He was so pissed off, he didn’t even say goodbye.
Jimmy Conway: Stop with those fucking drugs. They’re making your mind into mush. You hear me? Take’em back!

They don’t work, or not very well, and don’t go giving anyone ideas. Again, sticking anything in front of a gun muzzle, even a pillow, to muffle the sound, is a Federal crime unless you’ve filled out the paperwork and obtained a Class III tax stamp. It is seriously not worth the risk.


You don’t want me to give them ideas? Hey, watch it! One of us has never seen a gun other than on screen, much less thought about them at all until some gun nuts start going on and on about the fine points of spies and assassins. If it were up to me all guns would be melted down and silencers would be for cars.


One of us–I’ll leave it to the reader to figure out which–didn’t implicitly advocate manufacturing and using an illegal silencer. (Hint: see the person who wrote, “If those work, who needs a licenced silencer?”)

And there is a distinction–I’d like to think it’s a pretty clear one, but perhaps in what passes for your cognitive capability not quite so deliniated–between qualified information and the rantings of “gun nuts”, and certainly as distinguished from “something I remember from an episode of a notoriously technically inaccurate t.v. show.”


I had the opportunity once to fire a (lawfully owned) full auto suppressed Uzi with subsonic ammo. It was somewhat similar to the sound of an air ratchet (removing a nut from a bolt as opposed to free spinning) and you could clearly hear the sound of the action cycling as well as the bullets thudding into the mud and tearing through the vegetation. I would guess that someone unfamiliar with the sound would not recognize it for what it was if they did not see the firing.

Stranger, the whole reason I’d asked, here, was because there’s no way, absolutely none, that I’m going to fire any firearm through an improvised silencer that’s being held in my all-natural, orginal equipement, hand.

Thanks for the answer.

Glad to hear it. One of the rules strongly drilled into me during my otherwise mispent adolescence was “Don’t let an arm or a leg extend out past your muzzle,” the point being that it would be very easy for you to carelessly let a limb cross the muzzle line and therefore violate Rule #2: “Never let the muzzle cover anything you are unwilling to destroy.” Those guys on Miami Vice running around with their guns pointing straight down can look forward to losing a toe or a kneecap if they ever stumble while chasing a suspect.


Not to turn this into a debate or anything, but if silencers are legal (if controlled), I assume there must be some kind of non-spy non-assassin non-other-shady-purpose reason to have one. What’s that reason?

Noise control. Gunfire is very loud, and can spook both animals and the neighbours.

Silencers are completely legal in New Zealand and several European countries for this very reason.

During hunting, or at the shooting range, or what?