Why Are .22 Rifles So Quiet?

Ryan has this nice video up of shooting an old Remington 514T .22

Now there might be some other things at work here, but I suspect the key is the barrel length. Today most .22 rifles have a 16″ barrel, sometimes a little more just to make sure things stay legal, I’m not familiar with this rifle but some listings on gun sights have said it has a 23″ tube. I have an old Glenfield branded Marlin Model 60 that has the 22″ barrel with the 18-shot tube magazine. That gun is very quiet, and if I’m shooting it like Ryan is, alone on a private range, I don’t even bother with my ears. Ryan says the same thing, but doesn’t recommend it. I’ll go a step further after my little physics talk.

So first let’s talk about sound suppressors and how they work. The bullet exits the barrel and enters the suppressor, here the gasses start expanding in the baffle system, and when the cartridge exits the suppressor the gas slowly bleeds out into the atmosphere.

How this makes the gun quiet is when the gas exits the gun it expands to ambient atmospheric pressure. This is the same mechanic as when a balloon pops. That rubber party balloon feels hard to the touch because the gas is compressed. When you pop it, it rapidly expands to the ambient pressure, and this creates a shock-wave. I remember a kid in school who was a tinkerer, and he ended up tying off a 2 liter soda bottle to an air compressor and let it run. When the bottle gave way it left him with his ears painfully ringing. I’ve done a similar trick stuffing a drink bottle with dry ice and sealing it tightly. The bottle is stronger than the rubber balloon so the pressure difference is greater, and so the shock wave is greater. Scale that up to the gas pressure behind a bullet and we have the reason why you should wear ear protection on the range.

Now if you had a magic suppressor that reduced gas pressure behind the bullet to one atmosphere, your muzzle report would be zero. Now if the pressure inside the gun is 1 atm, and outside is 1 atm, the bullet will be experiencing as much pressure pushing it INTO the gun as outside the gun. This would probably work in a suppressor as momentum would probably carry the bullet out of the can. Still velocity would be low, and I wonder if the round would still have stable flight, or if you might start getting baffle strikes.

One other thing to note is that the suppressor working does make noise, as there is expanding gas. Still the shock wave created by this expansion is mostly containing inside the can. Still a thicker outer wall of the suppressor would make for a quieter can.

But let’s get back to the talk of the gun barrel. When people are discussing what barrel length for a gun it’s generally a game of weight/size/handling to muzzle velocity. A 10″ AR-15 is super handy, small, and light, but with that you have lower muzzle velocity. Incidentally you also have a louder gun with more pronounced flash. This is because more of the propellant gas is expanding outside the barrel than inside.

See where I’m going?

Now this isn’t a limitless property. If you stuck a 6′ barrel on your 10/22 you wouldn’t suddenly turn those CCI Mini-Mags into 5.56x45mm ammo. Eventually all the propellant will burn up, and the gas inside the barrel will expand to 1 atm, and if there is more barrel to go, air outside will push the bullet back and you’ll get a stuck round. Still moving backward from these numbers you will get more muzzle velocity and more noise coming out of the barrel, but for a while you’ll be getting a REALLY slow bullet until you reach a maximum, then you start losing velocity again, but instead of barrel friction and loss of gas pressure you’re losing velocity because you are essentially wasting the energy of the gas making noise.

So a longer barrel .22 is essentially acting as a suppressor, but rather than expanding the gas behind the bullet in baffles perpendicular to the plane of the barrel, you’re simply expanding gas directly behind the bullet in the ever growing barrel volume. Also given that gun barrels, even light weight ones, are MUCH thicker than the outside wall of a suppressor it actually does a more efficient job of keeping the gas quiet. Further the gas is expanding much slower because you don’t have the interface between the tight barrel and the more expansive body of the suppressor the sound of the expanding gas is less dramatic.

Also doing a little research to find the sweet spot for a .22 Barrel I found this forum post:

Supersonic speed is bad for .22 accuracy – if the bullet slows back below the speed of sound before it gets to the target (and it does) and is destabilized by the turbulence as it passes through the trans-sonic zone. So benchrest .22 target shooters shoot subsonic ammo. (Centerfire starts out supersonic and stays there.)

Target rifles don’t have long barrels just because of sight radius. Slowing the bullet a little by using a long barrel helps guarantee that the bullet does not reach the speed of sound.

In this thread and a few other pages I’ve read that maximum .22 LR velocity is reached somewhere between 14 and 18 inches of barrel length. This of course is highly subjective to the quality of the barrel (less friction, better velocity over longer lengths), the load used (more gas created, the more barrel that load will push the bullet through the barrel), and local weather conditions (the lower the air pressure the less the bullet will be pushed back into the barrel by outside air).

Either way a barrel over 20 inches is actually SLOWING the bullet down, and while it does that the gas behind it is decompressing. Further the barrel is soaking up the heat from the gas, making it lose pressure, and possibly the bullet is slowed enough that it isn’t breaking the sound barrier, which we haven’t discussed, but this also makes noise.

And there you have it!

Now I’ll take a step beyond what Ryan says. There is some debate on this, and sometimes you’ll see people shooting suppressed guns with ear protection, and sometimes you see them shooting without. When I’m at my gun club I’m ALWAYS shooting with eyes and ears because you never know when somebody with a .44 Mag, or an AR-15 with a muzzle break will start shooting next to you. Still when the range is strictly controlled I shoot suppressed guns and .22s with longer barrels without ears. They’re considerably quieter than when the train goes by my house, or a motorcycle downshifts as it passes me on the sidewalk, so I see no point in diminishing my hearing with ear protection. And for 20″+ .22s you’re essentially shooting a .22 pistol with a suppressor on it, or even better.

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6 Responses to Why Are .22 Rifles So Quiet?

  1. Alan says:

    When I’m shooting my Marlin 39a the shock wave from the supersonic bullet is louder than the sound from the shot.

  2. Ryan Michad says:

    Thanks for the post Weerd! Like Alan says above, the shot was actually louder when the sound of the bullet breaking the supersonic barrier was echoed back to us, reflecting off the hills around my range. It was the most strange thing. Me and the Mad Aussie have been shooting for years, and the rifle didn’t even trip his electronic muffs to shut them off when we fired. That was the first indication that something was up.

    • Weerd Beard says:

      So they were still going supersonic. That’s also an interesting fact given that standard velocity .22 is generally JUST supersonic out of a rifle. So you had enough barrel to eat up most of the gas pressure, but not enough to drop the velocity low enough to subsonic.

      Yeah sonic booms without the muzzle report are very interesting. I was shooting with Wally once in Maine and he had an M16 with a belt-fed .22 conversion upper with one of his .22 Cans on the muzzle. All you really could hear was the reciprocation of the action and the rounds breaking the sound barrier in a Doppler effect as they went down range. VERY cool.

  3. McThag says:

    I guess that would explain the excellent results from my Remington 341 that’s nearly Mosin long with its 27″ barrel.

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  5. Anonymous says:

    I’ve seen on the old guns.connect.fi web page the observation that, at least with some types of .22 LR ammunition, the propellant gasses are expanding at less than the speed of sound with a 28″+ barrel, as we see on some older target rifles.

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