Ask Foghorn: Does a Silencer Affect the Velocity of the Bullet?

I’ve had a number of people ask me the exact same thing after they learned I had recently received my first silencer. “Hey Foghorn, doesn’t a silencer slow down the bullet?” And to be honest, I had no idea. But I had a silencer, a chronograph and R loaded onto my computer and I was determined to find out.

While I was at AAC’s headquarters last year I learned about this idea that a silencer would slow down the bullet. Turns out that its based in fact — the early silencers used a rubber gasket (or “wipe”) at the end of the can that would contact the round and slow it down. The idea was that the gasket would contain the gases for a little longer as the bullet flew downrange quieting the gun even more, but the friction wore out the gaskets quickly and proved to decrease the velocity and accuracy of the rounds.

Modern silencers don’t use the wipes anymore. As AAC’s guys tell it, the silencers are machined to such precision that there isn’t much distance between the round and the baffles to begin with, and a wipe is unnecessary.

So what effect does a modern silencer have on ammunition velocity? To find out I headed out to the Bracken Range in San Antonio, Texas and set up a test.

Using the 762-SDN-6 silencer on a pair of upper receivers, I would fire 10 rounds with and without the silencer, recording the velocities for each round downrange. Then, using R I would plot those velocities and see if there was any distinct difference in the velocities observed between silenced and normal operation.

I used both 5.56 NATO and 300 BLK ammunition for this test, and while the 762-SDN-6 is indeed a 30 caliber silencer it is capable of suppressing the sound of 5.56 also — just not as well as a dedicated 5.56 can.

So what were the results?

For the 5.56 NATO ammunition there is an observed gain of about 20 feet per second with a silencer, but that gain is statistically insignificant. We’re talking about a 1-3% increase in velocity (which in the grand scheme of things is negligible), and R is telling me that the difference is more likely random sampling error than an actual difference. So, in short, nothing different.

For the 300 BLK ammunition there is no change in the velocity observed. The boxplot gets bigger for the silenced box, but it only does so because instead of firing 10 rounds like I was supposed to I fired 40 rounds. Why? Because it was a ton of fun, that’s why. Anyway, the difference in mean velocities is so small that I’m not even going to mention it. Again, statistically insignificant change in velocity.

So what’s the final word? According to what I’m seeing here a modern silencer does not change the velocity of the ammunition in any meaningful way. Sure it will throw your shots low, but that’s because the silencer is adding weight to the barrel and forcing it down. But that’s it.

[Email your firearms-related questions to “Ask Foghorn” via guntruth@me.com. Click here to browse previous posts]

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About Nick Leghorn

Nick Leghorn is a gun nerd living and working in San Antonio, Texas. In his free time, he's a competition shooter (USPSA, 3-gun and NRA High Power), aspiring pilot, and enjoys mixing statistics and science with firearms. Now on sale: Getting Started with Firearms by yours truly!

28 Responses to Ask Foghorn: Does a Silencer Affect the Velocity of the Bullet?

  1. avatarJames says:

    Wouldn’t it be correct to say that, in proper use of a silencer, subsonic ammunition – by definition, slower than standard ammunition – has to be used anyway?

    You don’t mention in the text, but was subsonic ammunition what was used to get your figures? Based on the FPS values listed, it doesn’t look like you did. Correct me if I’m wrong, but subsonic ammunition, ideally, should be in the 700-800 FPS range, not 2400 and 3000+ as indicated in your graphs.

    I mean, I see the question you were asked and the answer you’re offering. But isn’t that like asking the benefits of mid-grade or premium on engine performance over regular unleaded, and then using 120-octane avgas to derive an answer?

    • avatarry_ry says:

      .300 AAC/BLK is offered in both subsonic and supersonic rounds.

      I didn’t read where he stated he was using subsonic, although it’s logical to assume that he would with a suppressor.

      • avatarfrankgon4 says:

        The data displayed indicate 3000 fps which is more than twice the speed of sound. Looks like he used standard ammo and not subsonic.

    • In this case supersonic / subsonic ammunition doesn’t matter. If the velocity of a supersonic round would be impacted then the velocity of a subsonic would as well, and vice versa. Supersonic rounds don’t have some strange quality that makes them impervious to the laws of physics.

      • avatarJames says:

        True, but I would think that the slowdown would be greater on a subsonic round, as the forces acting on it are of higher proportion than when acting on a supersonic round.

        While the affect isn’t as pronounced with supersonic ammo, giving what appears to be a 20-40 FPS average slowdown, might be more noticeable on a round that’s moving two to four times slower to begin with – such that

        20fps slowdown/2400fps base speed = 0.83% slowdown

        …and, assuming you can expect a .83% percent slowdown on all your rounds

        .83% * 800fps base subsonic speed = 66.4fps
        800fps base subsonic speed minus 66.4fps slowdown = 733.6fps after-silencer speed

        Again, probably not very noticeable to the shooter, but definitely a more pronounced effect.

        • Which would be true if the ammunition was slowing down. On the contrary, the ammunition appeared to be speeding up with the silencer attached. Not a statistically significant speed-up, but its there in the chart.

          I get what you’re saying, and I’ll be perfectly happy to re-try with subsonic ammo later this week.

        • avatarDaver says:

          You have it backwards. The common knowledge on the silencer gun boards has always been that suppressors give you (if anything) a slight velocity *boost* due to more efficient use of the powder. So the results here are perfectly in line with what everyone reports. And yes, that trend holds true for sub sonic ammo as well: suppressor=greater average velocity.

        • avatarMark says:

          James, your math is wrong. 20fps is .83% of 2400fps. But .83% of 800fps IS NOT 66fps. it is 6.6fps. so the first would have an after silencer of 2380 fps and the subsonic would have a speed of 793.4 fps. Keep track of the decimal points…..

        • avatarJames says:

          I see what I did – .083 instead of .0083

          Decimal points, indeed.

    • avatarLia says:

      When was the last time the barrel was clneead to remove the fouling?With .22s they often build up a lube track from the lead deposits. If the lube track is getting heavy enough the standard and low velocity rounds may be going slow enough to not be stable. Another option is at the slower speed the bullet may pick up excess deposits or shed more weight throwing off the center of gravity.The high velocity rounds may be going fast enough and have enough pressure to not have a problem with the lube track.If it has been clneead, I would do it without the can on and see what happens. If it still tumbles break out a chrono and make sure you’re getting expected velocities. It is a mysterious problem keeps us updated. I’m interested in hearing what the final root cause is.

    • avatarShonatay says:

      So, they caught a cpluoe of criminals selling illegal firearms. What does this have to do with the vast majority of decent, law abiding gun owners who not only did not do anything illegal, they wouldn’t even contemplate anything like this? But then, the ATF has to point to the odd criminal to justify ts own miserable existence, and its own history in trafficking arms to the worst killers in North America the Mexican drug cartels in a patently hairbrained scheme that left at least two Federal officers and likely hundreds of innocent Mexicans dead. If anything, the entire outfit deserves to be institutionalized for mental retardation considering what it has Achieved on the whole.

  2. avatargreat unknown says:

    and being a pedant, I would appreciate if you would edit the Headline to read “affect” instead of effect. as long as we’re talking about “final words”

  3. avatarfrankgon4 says:

    Appreciate the data. I do have some questions about using a “silencer”.
    How quiet is a 5.56 or 300 Black when using a silencer with bullets that travel faster than sound? Is there a loud crack as the bullet breaks the sound barrier?
    Is it standard procedure to use rounds faster than the speed of sound or does it not make a difference?
    I never wanted a ‘silencer’ as I thought you had to use subsonic bullets and felt the trade off of power would be too great. If these work with standard ammo, I would take another look.

    • Supersonic rounds will still be “hearing safe” with a silencer. The supersonic crack is mainly an issue downrange, so you standing behind the gun won’t have much of an issue.

  4. avatarJWhite says:

    But in Call Of Duty silencers only reduce damage. I mean, I’m pretty good at that game, I could be special forces or something.

    *eye roll*

    Damn vid-ya games

  5. avatarIdahoPete says:

    OK, I will type this post v-e-r-y slowly – - -

    Did you notice any change in bullet group impact with and without the silencer? I have noticed a change in impact with some of my rifles with/without the flash hider and/or compensators, and wonder if a silencer changes the point of impact.

    • avatarDaver says:

      He already said: “According to what I’m seeing here a modern silencer does not change the velocity of the ammunition in any meaningful way. Sure it will throw your shots low, but that’s because the silencer is adding weight to the barrel and forcing it down.”

      • avatarIdahoPete says:

        As a general rule, you adjust your sights based on groups fired from a rest, not offhand. That would not allow the silencer weight to force the barrel down. If he is testing it from a rest and the shots are grouping lower with the silencer than without, that represents a change in the bullet impact. If Mr. Leghorn is testing from an unsupported position, that is information I did not see in the post. I can’t tell if the rifle had a bipod, and no sandbags are visible in the photo of the bench. I would also note that this report concerned velocity, not accuracy – my question was specific to group size and location.

        • avatarBen says:

          “I would also note that this report concerned velocity, not accuracy – my question was specific to group size and location.”

          Then perhaps you could have considered asking in a less-dickish way? Since per your own admission, that wasn’t part of the initial test.

          I’ll type this very slowly, to make sure you follow:

          You’re right, shooting from a rest means the weight shouldn’t matter, but at the bottom of the article Nick does mention that the gun shoots low with the suppressor attached. Since the velocity is the same (and quite consistent) the bullets are following the same ballistic path once they leave the barrel. So if they’re hitting differently it’s because the can altered their course in some way before they left the gun. My guess is the can changes the harmonics of the barrel – just like shooting an old WWII rifle with and without a bayonet attached. The barrel flexes during firing and the extra weight changes the frequency. The bullets still leave the gun in a consistent way and still group just fine, but with a different point of impact. One quick adjustment to the sights and you should be as good as ever.

  6. avatarKendahl says:

    The verb should be “affect”, not “effect”. (I know; I’m just being picky.)

  7. Where did you measure from when you tested it while silenced? The end of the silencer or the end of the barrel?

  8. avatarMike Settles says:

    I doubt that the weight of a suppressor would “throw the bullets low”. Instead, it’s probably a change in barrel harmonics.
    Several months ago I tested the myth that a rifle would shoot differently if you fixed bayonet: It’s true. I used my Bushmaster AR15E23, 20 inch barrel with 1:9 twist, firing two groups (one with, one without the pig-sticker) using Federal XM193 ammo. The result: “With bayonet” grouped about four inches low at 100 yards. No real change in group size. I discussed the results with several of the gray-hairs on the range, and they suggested barrel harmonics as the source of the change.

  9. avatarJuan says:

    I’d say fouling is liekly, made more liekly by the can. You could have had a baffle strike and the can is causing the key holing. First step is to get the can off and clean both the can and the gun. If you can take the can down, do it and check each baffle. Check the crown on the barrel (very common source of key holing) You could spend a lot of time trying to figure out why it’s key holing, but I can almost guarantee you that once you have everything torn down, the answer will be obvious.Or you can send it to me and I’ll fix it for you

  10. avatarEJ says:

    A slight (but insignificant) boost in velocity is just about right. Think of it this way- by adding the suppressor to the barrel, you’ve added barrel length: the bullet is being pushed from behind by combustion gases longer. However, since the suppressor has room for those gases to expand into, the gas pressure in it is much lower than if it were simply added inches of normal barrel, and so the boost in velocity is only slight, e.g. it’s like adding an additional amount of normal barrel a fraction of the length of the suppressor.

    Another slight effect is that the bullet goes a little faster simply because the gun looks cooler with a suppressor on it and the bullet wants to live up to that coolness by improving its own performance :)

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