Never used any hearing protection in Viet Nam, and even with today's advances, would not use any hearing protection in combat today. For training yes, for the range yes, for combat, NO.
In combat the noise is unbelievable, with peaks and valleys from intense fire to single fire to no fire, even hearing protection like my Peltor 7's which allow me to hear conversation at the range but block out loud noises like gunfire, with gunfire going on in a firefight, you need to hear voice commands, you need to hear the radio to call in fire missions or medivacs/dustoffs, you need to hear enemy movement and incoming versus outgoing rounds, an AK has a different cyclic rate and sounds different from an AR, etc.
So even today hearing loss and tinnitus, ringing in the ears, is just a part of the price we all pay for combat.
Combat does strange things to you, we went into a hot LZ once by helicopter and when I got off the bird I could not hear for about ten minutes, and it was terrifying, I was twenty years old then and there was nothing wrong with my hearing and I did not do it intentionally I just think subconsiously my mind shut down my hearing. I have also experienced tunnel vision and things happening at light speed but in slow motion to me, all these are real but caused by your mind as I did none of them intentional, out in the jungle I did not like to sleep at night or sleep very well, as your senses, sight and hearing are shut down during sleep, forget alcohol and drugs even if you could get them out in to the field, only a fool would use them and lose complete control of your senses.
I worked as a Veteran's Rep for most of my career, and filed many claims for Veterans for GI Bill, Home Loans, VA Health Care, Veterans Pension, and Service Connected Disability Compensation, two claims I filed before I retired are memorable, one was for a Navy World War II Vet who was in the Pacific firing those four Quad 40 Pom Pom guns at Japanese aircraft, the other was for a 11 Charlie Korean War Vet in artilley who fired thousands of artillery rounds, God Bless those Gentlemen and all the Veterans I was lucky enough to serve, both received small VA Compensation checks each month for hearing loss and ringing in the ears, fifty years after the fact.