Thread: Noise level of subsonic calibres

Fellas from your relevant long guns, how do you rank the noise comparitively.

Say between calibres, 38, 357, 44 mag, 45 acp, 45 colt, and rifle barrels, not pistols, subsonic loads and lets say for the argument, not with supressor, just the bare rifle noise. Bigger calibres are always noisier?

Pressure at the muzzle is the main factor for peak noise. Sounds is exactly that - pressure waves. Bigger pressure differential = louder noise. When suppressors come into play, all else being equal, smaller bore is quieter as it's easier to capture the gas.

Of the ones you listed, my guess is 45ACP will be the quietest without a can. Small amount of powder, and pressure has plenty of barrel to drops off in before reaching the muzzle. It has the benefit of being so far below the sound barrier that the air it's displacing doesn't go supersonic either.

Ok interesting. But I think all else being equal 38, 45colt and 44 magnum subsonic, say pushing them to 1000fps, you can always get lower pressure as they are bigger cases for their calibre. Checking hodgon reloading data and 38 sp are running about 17000PSI max, 45 and 44 can be running as low as 14,000PSI, the 45acp is 20,000PSI with factory. Will it still be quieter? My only experience is 38/357 so I cant compare ito the others.

i wouldnt bother with subsoincs without a suppressor

shorter barrel = louder without suppressor

smaller bullet pushes less air out of the way the same way a slippery road bike does compaired to a mac truck

Originally Posted by sixtus

Ok interesting. But I think all else being equal 38, 45colt and 44 magnum subsonic, say pushing them to 1000fps, you can always get lower pressure as they are bigger cases for their calibre. Checking hodgon reloading data and 38 sp are running about 17000PSI max, 45 and 44 can be running as low as 14,000PSI, the 45acp is 20,000PSI with factory. Will it still be quieter? My only experience is 38/357 so I cant compare ito the others.

The figures you see online are a measure of chamber pressure not muzzle pressure. The 20k psi of the 45acp is only within the confines of its little case.

E.g. 300 blackout and 308...

The blackout with a much smaller case will create much higher peak pressure (accelerating the bullet very nicely), but with less powder there's less total gas volume and by the time it's expanded all the way down the barrel, the will be very little muzzle pressure. Exhibit A:



308 with a much larger case, needs more powder to generate enough pressure to accellerate the bullet. Chamber pressure might be lower, but the extra gas created by the powder results in more pressure at the muzzle. Exhibit B:

.45/70 through long barrel with mild load isnt unpleasant on ears at all....mates rossi .45long colt is somewhat like but less than .410 shotgun (which Ive always said has weird sound,almost like its being shot down a drain pipe)subsonic .22lr through long barrel is ALMOST as quiet as with suppressor.

Originally Posted by PommyMcPomFace

The figures you see online are a measure of chamber pressure not muzzle pressure. The 20k psi of the 45acp is only within the confines of its little case.

E.g. 300 blackout and 308...

The blackout with a much smaller case will create much higher peak pressure (accelerating the bullet very nicely), but with less powder there's less total gas volume and by the time it's expanded all the way down the barrel, the will be very little muzzle pressure. Exhibit A:

Attachment 123548

308 with a much larger case, needs more powder to generate enough pressure to accellerate the bullet. Chamber pressure might be lower, but the extra gas created by the powder results in more pressure at the muzzle. Exhibit B:

Attachment 123549

I understand that but the point is whether for 38, 44, 45 colt, 45acp etc the breech pressure would correlate to the drop in muzzle pressure as they are all running fat pistol bullets and tiny charges of powder. Similar expansion ratios? Or would the 45 ACP starting out at 20,000PSI finish hotter than the others at the muzzle as well?

I guess the easy way to work out breech pressure it to plug the data for these calibres into quickload, wish I had a copy

Originally Posted by Bill999

i wouldnt bother with subsoincs without a suppressor

shorter barrel = louder without suppressor

smaller bullet pushes less air out of the way the same way a slippery road bike does compaired to a mac truck

Im in Australia, no supressors, well none people admit to anyway. Its more of a general question and applicable to something like say cowboy shooting. aka which pistol calibre firing tiny sub charges generates the most noise.

in that case the bigger the hole the bigger the noise.......it even works that way suppressed. think its the tone as much as the volume.

Originally Posted by sixtus

Im in Australia, no supressors, well none people admit to anyway. Its more of a general question and applicable to something like say cowboy shooting. aka which pistol calibre firing tiny sub charges generates the most noise.

So you can shoot cowboys over in Aussie but you can't have suppressors?
Strange country.

Originally Posted by sixtus

Im in Australia, no supressors, well none people admit to anyway. Its more of a general question and applicable to something like say cowboy shooting. aka which pistol calibre firing tiny sub charges generates the most noise.

The only way to tell is to use a Decibel meter to measure the sound level of each calibre the human ear is crap at telling the sound level, any Health a safety company will have them
you maybe able to rent one.

yeah but then I need all the calibres present to test. Could possibly do it at a cowboy action shoot if I can find one...