At the indoor range during cease fire a shooter had an accidental discharge with his .357 magnum, I was standing only a couple of feet next to him with my earmuffs off. I couldn't hear anything for the rest of the day and on the next day it was like having water in my ears.
The second loudest noise I ever heard was shooting a short shotgun without ear protection, but this time outdoors. It was really painfully loud, even with standard pressure 00 buck. It wasn't a loud BOOM, it was an earsplitting ''crack'' that would totally blow my eardrums out indoors.
Last but not least a 8mm Mauser K98k without earmuffs outdoors, even though that round had much MUCH more pressure (and with 200 grains @ 2600 fp/s it was a hot load) and a much bigger powder charge than the 357 or the shotgun round the sound was...bearable.
Not something I'd recommend doing but I think touching off a couple of rounds outdoors does no result in complete deafness or ringing ears for hours. Its more of a loud boom that hurts a little bit.
I think the volume of the sound depends on the powder burning rate, according to my experiences the faster powder is louder and pressure or charge weight has nothing to do with. Shotguns use the fastest powder, flake powder, next his handgun ball powder and the slowest is the rifle using stick powder.
Unless muzzle brakes are involved, they make all guns extremely loud.
YMMV
Oh, and for the record, I got my hearing checked, my ears are still as good as when I was 7 years old.