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.

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