Most important feature is the Noise Reduction Rating (NRR). According to my Audiologist, the minimum rating is 23 decibles - NRR 23. Hope the information helps.
I shoot 72.3 grains of H-1000 in my 7 LRM @ 3027 fps with 1/4” groups at 100 yards. After 1063 rounds fired, the rifle maintains its precision. My bullet of choice is Berger 180 grain Hybrid Target. Hope this helps.