I own a 300 BLK AR and I get that one of the driving things behind the cartridge is the use of subsonic ammunition in an AR-platform carbine. However, I am still on the fence about using subsonics in a defensive role. At this point there might be one or two ammo offerings out there that provide reliable expansion at subsonic velocities but choices are limited.
My question is around the combination of a suppressor and supersonic ammunition. Obviously there will be more noise with supersonics, but I have read conflicting information about just how much. Some people say just the sonic crack will register 140 dB, which is right at the OSHA-stated hearing safe threshold (and I don't consider that hearing safe, especially for people like me who have hearing damage).
I bought a SilencerCo Omega for my gun which was just recently approved by the ATF (yay!). On their web page, SilencerCo rates this suppressor at the following noise levels at the muzzle:
300 BLK -- 119.5 dB (my assumption is subsonic ammo)
5.56 -- 130.1 dB
.308 -- 133.9 dB
This suggests the noise from the bullet breaking the sound barrier may be less than some suggest. I plan to use earpro when shooting anyway, but am trying to gauge how damaging it might be if I ever have to shoot non-suppressed. I would expect suppressed 300 BLK from a 16" barrel to produce slightly less noise than 5.56 because all the powder will have burned up inside the barrel. It will still be loud because of going supersonic -- but perhaps in the upper 120 dB range? Or does the sonic crack take it well over that?
Do suppressor manufacturers noise level ratings take the sonic boom/crack into account?
Even target pullers at Camp Perry have to wear earpro when working the pits -- this makes me wonder how the sonic crack works. Does it occur just at the point the bullet breaks the sound barrier or does a supersonic projectile continue to make noise as it travels? I always assumed it just occurs once as the sound barrier is broken. I realize this part is mostly an academic question.