Suppressors only really suppress subsonic ammo. They take the bang of the rifle out, but the supersonic flight of the bullet still produces a sonic boom that is loud. IMO it isnt worth having a suppressor and shooting full power ammo. They only work very well for what they arent intended for - subsonic ammo...
And ill reinterate.. with full power loads, yes the bang of the rifle is quieter, but as a whole its all still loud.
This isn't true at all. A good suppressor will knock .223 down from 175dB to 135dB. A change of 10dB is about halving or doubling the perceived loudness. So that .223 is SIXTEEN TIMES LOUDER without a suppressor.
A suppressed 300 Blackout or 22LR subsonic is about 115dB, or FOUR TIMES quieter than the suppressed .223 supersonic ammo. That's a big difference, but the huge step is from un-suppressed supersonic down to suppressed supersonic.
Put another way - great earplugs give you about 33dB attenuation. An average centerfire suppressor gets you 30dB. A great one gets you 40dB. They are more effective than earplugs. This is awesome on a hunting gun - I use a suppressor on my 17 HMR, and it lets my son and I walk around after woodchucks with no ear pro, without me worrying about damaging his young ears. It's still loud enough for the neighbors to hear, but it's very comparable to a firecracker - not painful or damaging.
A semi-auto, especially a gas gun like an AR-15, will not quite see those reductions at the shooter's ear. My 6.5 Creedmoor with Omega would probably meter about 140dB using the mil-standard test, 1m to the side of the muzzle. My 11.5" AR-15 with the same suppressor meters about 135dB in the same test. But, at my ear, the 6.5 is actually a little bit quieter. Why? Because the can is on the end of a 24" barrel, not an 11.5" one, and there's no gas and action noise right next to my ear.
Also, a suppressor decreases felt recoil, while making the gun quieter. A brake makes a gun LOUDER, which is lousy for everyone on the firing line, although they are more effective than a suppressor.
A few more anecdotes to provide people with an idea of what to expect:
Suppressed sub-sonic bolt guns are really James Bond quiet. I literally shoot my suppressed .22LR handgun with my youngest asleep nearby. He doesn't stir. Being able to shoot behind my garage without bugging anyone in the house is really a game-changer. I get so much more practice in now.
A suppressed 17 HMR is pretty quiet, about like a firecracker. A full-size rifle can with large baffles is highly ineffective, but a rifle can with .22 baffles can be very good.
Suppressed super-sonic 22LR is quieter, and comfortable to shoot, but very similar to .17 HMR. Lots of crack.
Suppressed super-sonic centerfire guns are as loud as subsonic 22LR ammo with no suppressor. It's more of a "boom" than a "pop" in tone, but sound levels (and hearing damage or lack therof) is very similar.
It's about the same as shooting the same gun with a single layer of ear pro, in terms of SPL. It's different because you hear the crack more clearly, and the echo of the blast, but peak levels are similar. I still run ear pro for range sessions, but firing a good centerfire suppressor is under the OSHA standards - if someone was firing a centerfire rifle every hour on the hour at your workplace, OSHA would have no problem with employees not wearing ear pro.
Being able to wear electronic muffs with only 22dB of reduction and still adequately protect my ears is awesome. And being able to hunt with zero protection and not hurt my ears is a game-changer.
Plus, my range is in the middle of a 600-acre farm, but on a hilltop. There are at least 6 neighbors than can hear me shoot un-suppressed. A long range session might eventually grate on them if I'm booming away with a 300 WSM or short-barrel AR, while they try to nap on the porch. With a suppressor, all they hear is the ring of steel.
So to summarize:
Suppressed sub-sonic ammo is awesome. It's quieter than a high-powered pellet gun and massively more powerful.
Suppressed supersonic small-caliber stuff like 17 HMR still cracks, but makes blasting critters with a centerfire a no-earplug experience. I muff up for long range sessions.
Suppressed centerfire is a real game-changer. I still wear pro for range sessions, but it lets me shoot or hunt in places that I couldn't otherwise, and makes all my range sessions more pleasant. I used to feel wrung out after a long .308 or 300 WSM session, and blamed it on recoil - but I think it was blast. I can shoot hundreds of centerfire rounds in a session and not feel beat-up after. I'll never own another centerfire without a threaded barrel (except a real light hunting gun).