If you hear the "crack of a supersonic bullet", YOU'RE STANDING IN THE WRONG PLACE.
Yup, and if you "heard" it, you probably ought to get down.
So, we don't hear the crack standing behind the bullet/gun??
Yes and no. You will hear it, but it will be downrange awhile when you do, and not an issue to your hearing.
I have a suppressor for my AR, and can shoot it in the carport without hearing protection, something I cant do with a .22LR. Same goes for my Glock with its suppressor when super sonic ammo is used. Its the muzzle blast thats bad for your ears.
“The enemy is anybody who's going to get you killed, no matter which side he is on.” ― Joseph Heller, Catch-22
Beware of associating with "Cheap" Squirrels. They tend to be very narrow minded, hypocritical, and will gag you if you question or disagree.