My first MOS was 13B (Field Artillery Crewman), then OJT 13E (Fire Direction). Also 13C and 13D. Also Pershing Missile Officer and Cannon Officer. My Fire Direction Center was never more than 150 feet (50 meters) from the 155mm (M109 through A5) gun line. I always made a point of spending time on the gun line. Standing by the side of the M109 as it fired, riding the recoil inside the cab, feeling the over-pressure in my chest before the sound registered on my ears.
All we wore were plastic, triple-flange ear plugs. Same for the rifle range, M2, or gun line. In my FDC, we did not wear ear plugs. I also wore these when on the 8 inch howitzer gun line.
The VA says I've lost a little of my high frequency hearing, but no more than is normal for a man my age. I tell my wife it's the same frequency as the average American female voice.
Cannoneers know what loud is.