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Does barrel length affect suppressed sound levels?

I think I’ll do an experiment:

With hyper-velocity .22 lr ammo like CCI’s Stinger, I’ll shoot one shot thru a suppressed Ruger 10/22 with a 22” barrel, then move the can over to a 5” barreled Browning Buck Mark, and shoot the same Stinger ammo.

I’ll need to take a couple fouling shots first, to take away “first round pop”.

Or, let BOTH guns do one shot thru a cold can, with fresh air in it, so both shots will have some FRP.

Will the Stingers stay supersonic out of the 5" barrel?
 
I think they’ll be supersonic.
Many brands of 36-40 grain cheap high velocity .22lr come out supersonic. Some don't. For the normal "hi speed" or "high velocity" ammo, some give me the supersonic crack out of the BuckMark, and some will not.

The 30-grain Stinger with a published rifle velocity of 1500 fps should still go Mach 1.0 in five inches.
According to Ballistics by the Inch, with a CCI Stinger you have to go down to 3" of barrel to keep them subsonic.

So, I'll do this experiment with ammo that will be supersonic out of either host weapon.

I ALREADY KNOW that with subsonic stanrdard velocity target ammo, there is no difference that I can tell with my bare ears. Both sound like an AirSoft gun. Rifle or pistol both are nice and quiet, no matter whether the barrel is 3.2" (on my Walther P22), 5" (Buck Mark), 18.5" (standard Ruger 10/22 barrel) or 22" (Green Mountain barrel on the 10/22.)
 
I think they’ll be supersonic.
Many brands of 36-40 grain cheap high velocity .22lr come out supersonic. Some don't. For the normal "hi speed" or "high velocity" ammo, some give me the supersonic crack out of the BuckMark, and some will not.

The 30-grain Stinger with a published rifle velocity of 1500 fps should still go Mach 1.0 in five inches.
According to Ballistics by the Inch, with a CCI Stinger you have to go down to 3" of barrel to keep them subsonic.

So, I'll do this experiment with ammo that will be supersonic out of either host weapon.

I ALREADY KNOW that with subsonic stanrdard velocity target ammo, there is no difference that I can tell with my bare ears. Both sound like an AirSoft gun. Rifle or pistol both are nice and quiet, no matter whether the barrel is 3.2" (on my Walther P22), 5" (Buck Mark), 18.5" (standard Ruger 10/22 barrel) or 22" (Green Mountain barrel on the 10/22.)

Ok. I've never shot CCI Stingers and had to look up the velocity so yeah I think they will still be supersonic out of the 5" barrel.
 
The three main factors that affect noise levels are:
1/ Pressure at the muzzle
2/ Action noise
3/ Speed of the bullet

A suppressor only affects 1, the pressure at the end cap is significantly less than the pressure at the muzzle. A higher muzzle pressure will probably result in more pressure at the suppressor end cap, so all else being equal a shorter barrel will be louder even with a suppressor. Here's some info on that: https://ndiastorage.blob.core.usgov...0/armament/WednesdayCumberlandPhilipDater.pdf
This is why many suppressors are rated for a minimum barrel length.
The nice thing about 300 blackout is that it burns most of the powder within 9 inches of barrel, so a 10" barreled 300BLK won't be noticably louder than a 16" (both suppressed).

The action noise on a suppressed semiauto can still be quite loud, and on a direct impingement rifle (AR15) is also affected by the gas tube pressure. So all else being equal, a mid-length gas system will be slightly quieter than a carbine length gas system.
A suppressed 300 blackout AR15 has a lot of action noise, the main advantage being that it will cycle with subsonic ammo. It will still be louder than an unsuppressed subsonic 22lr though.

The speed of the bullet determines the magnitude of the sonic crack. A 22lr travelling 1200 fps will sound like a whip cracking, the crack of a .223 travelling 3000 fps is much louder.

If you want to be as quiet as possible, go with a bolt or lever action or single shot. If you reload you have lots of options. A subsonic 300 blackout is the same as a subsonic 308 - but a supersonic 300 blackout only has the energy of the supersonic 308 at 400 yards. If you want to load heavy subsonic bullets in a 308, make sure to get the fastest twist rate you can (1:10 or less).
 
A suppressed 300 blackout AR15 has a lot of action noise, the main advantage being that it will cycle with subsonic ammo. It will still be louder than an unsuppressed subsonic 22lr though.

I wouldnt say that a suppressed 300blk using subsonic is louder than an UNsuppressed .22. Subsonic 300blk suppressed with a decent can is mid 120db range. An unsuppressed 22 is around 155db. Suppressed a .22 pistol is anywhere from 115-120db. Even suppressed 5.56 rifles are quieter than 140db
 
I did the test.
3 different guns: a pistol with a 5" barrel, a rifle with a 22" barrel (and then an unsuppressed shot from an 18.5" barreled rifle).

I shot the pistol and the 22" rifle with the same silencer, an AAC "Pilot" on it. Cold, minutes between each shot, with fresh air in the bores and between the baffles. So there was first round pop.

RESULT: The pistol seemed louder, but not by that much. Not enough to make one acceptable for backyard pest control or plinking while the other barrel length would be unacceptable.
But the rifle barrel was definitely quieter.

ONE OTHER OBSERVATION: Both guns were pretty loud, even suppressed. I think that's due to a combination of First Round Pop (FRP) and the supersonic muzzle velocity (1600 f.p.s.)
And I think that's my perception because I did this test off my back deck (with a safe backstop), and I don't normally shoot here. I'm not "used to" hearing gunshots in my backyard.

Just for comparison, I brought out a different rifle, 18.5" barrel unsuppressed, and shot one Stinger through it.
It was only marginally louder than the .22 pistol with the suppressor in place. Not really a big, order-of-magnitude difference.

REMINDER: My test involved dramatically different barrel lengths. If you're trying to decide between a centerfire rifle round fired out of a 12" barrel vs. a 16" barrel, or the difference between a 16" AR carbine upper vs. a 20" AR barreled upper, I don't think those two or four inches would mean much --when using a suppressor, or when not.
 
The three main factors that affect noise levels are:
1/ Pressure at the muzzle
2/ Action noise
3/ Speed of the bullet

A suppressor only affects 1, the pressure at the end cap is significantly less than the pressure at the muzzle. A higher muzzle pressure will probably result in more pressure at the suppressor end cap, so all else being equal a shorter barrel will be louder even with a suppressor. Here's some info on that: https://ndiastorage.blob.core.usgov...0/armament/WednesdayCumberlandPhilipDater.pdf
This is why many suppressors are rated for a minimum barrel length.
The nice thing about 300 blackout is that it burns most of the powder within 9 inches of barrel, so a 10" barreled 300BLK won't be noticably louder than a 16" (both suppressed).

The action noise on a suppressed semiauto can still be quite loud, and on a direct impingement rifle (AR15) is also affected by the gas tube pressure. So all else being equal, a mid-length gas system will be slightly quieter than a carbine length gas system.
A suppressed 300 blackout AR15 has a lot of action noise, the main advantage being that it will cycle with subsonic ammo. It will still be louder than an unsuppressed subsonic 22lr though.

The speed of the bullet determines the magnitude of the sonic crack. A 22lr travelling 1200 fps will sound like a whip cracking, the crack of a .223 travelling 3000 fps is much louder.

If you want to be as quiet as possible, go with a bolt or lever action or single shot. If you reload you have lots of options. A subsonic 300 blackout is the same as a subsonic 308 - but a supersonic 300 blackout only has the energy of the supersonic 308 at 400 yards. If you want to load heavy subsonic bullets in a 308, make sure to get the fastest twist rate you can (1:10 or less).

300blk subs and 308 subs cant be the same pressures. if so why would the tirant 45m or any 300blk subsonic only suppressor not be able to be used on a 308 with subs ? AAC told me the pressures are too high. I was going to just use my 308 and do just that but instead ill be looking for a 300blk as well. Dont you want a slower twist rate for heavier bullets ? the sig rattler for instance is 1:5 its way faster of a twist, and aac states 1:8 is the fastest twist recommended to prevent spinning a heavy bullet out of control and causing a baffle strike . so it should read, if you want to use heavy subs, make sure to get the slowest twist rate you can, 1:10 or more , or am i wrong ?
 
300blk subs and 308 subs cant be the same pressures. if so why would the tirant 45m or any 300blk subsonic only suppressor not be able to be used on a 308 with subs ? AAC told me the pressures are too high.

Too many variables to say definitively. With the availability of powders we have I don't see why not though. I think AAC's comment would likely be driven by commercial/warranty concerns than actual technical ones, which is what I would expect from a manufacturer.

Dont you want a slower twist rate for heavier bullets ? the sig rattler for instance is 1:5 its way faster of a twist, and aac states 1:8 is the fastest twist recommended to prevent spinning a heavy bullet out of control and causing a baffle strike . so it should read, if you want to use heavy subs, make sure to get the slowest twist rate you can, 1:10 or more , or am i wrong ?

For a given diameter, the heavier a bullet gets, the longer it gets. Longer bullets need to spin faster than shorter ones to be stable once outside the barrel. (it isn't so much the length as opposed to the ratio of length to width... ideally 1:1 ratio is best, which would give you a round ball). Slower and faster are relative terms, so you really need to crunch the numbers to determine the best twist rate. Typically a .30 cal like .308 win or .30-06 will be 1:10 or 1:12. Ideal for .300BO is 1:8

The faster you spin a bullet, the thicker you have to make the jacket to make the bullet hold together, otherwise it will pull itself apart once it leaves the barrel on the way to the target.

Here's a tool you can play with to see the effects - http://www.bergerbullets.com/twist-rate-calculator/
 
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