I once put 6 rounds through a big ole' Colt .357 (custom loaded pretty hot....we were bored late at night) without plugs. The upshot is that the shockwave from missed rounds was strong enough to crumple aluminum cans. The down shot was that I couldn't hear voices right next to me for 3 hours, and the ringing / itching / pain didn't go away for almost a week. I don't know if there is any real long term damage from that session as I have not been tested recently before or since, but I will never fire anything bigger than a .22 without muffs or plugs after that experience. I can only imagine that combat soldiers take a serious auditory beating.
Sharp as a cue ball...but moving faster.