MachIVshooter
Member
But I would disagree, based on my experience having to play tight "man coverage" as an RO to keep the timer working on some of these guys, that blowback 9mm PCC's are inherently louder.
Unsuppressed, certainly not. The muzzle noise will be higher than port noise on an unsuppressed carbine, say 155 muzzle and 140-ish port. But suppressed, you increase backpressure, so port noise tends to creep up a few dB, while muzzle end will likely be in the arena of 120-125 with subsonic loads and mid-130s with supersonic rounds. Conversely, locked breech 9mm pistols are gonna run in the high 150s/low 160s muzzle and but mid-high 120s with subsonic ammo through your average full size 9mm can, while shooter's ear numbers tend to still be sub-130.
Gas guns are a mixed bag, but most will have piston pop in excess of 140 dB, regardless of muzzle SPL. ARs with properly tuned gas systems & buffers can get shooter's ear numbers into the high 130s.