.308 Norma Magnum at age 16, it's the only Hi-power rifle I've ever fired (only once

) w/o hearing protection. My ears rang with a painful squeal not allowing me to hear people talk for 40 minutes.
It did damage my hearing permanently, but fortunately not in a functional way as I'm still able to pass professional hearing exams, although it is noted (every time I get my ears tested) that I've been exposed to an explosion or other very loud noise that has caused an impairment.
Needless to say I've never forgotten my hearing protection since.
Cheers D