That is why the bullets were quiet. Thanks so much for giving me such great information.
I don't know why the bullets were quiet for you. For me, and everyone else I've done it with, .308, .223 and several other calibres went 'crack' at every range from 200 up to 800 yards. As a result, hearing protection was required by range rules. 45-70, otoh, was as you described. More of a whisper and then thunk.
You are, however, still incorrect re: supersonic booms. I look forward to your eventual graceful acknowledgement of same.