Under 3000 is a good rule of thumb for AR500. Even below 3,000, you may see some dimpling with ball ammo. I've dimpled AR500 at 200yrds with 223rem FMJ, at the same hanger and on same target where thousands of expanders had never made a scratch. For 1/2" or 3/8" AR500, as a rule, the energy should be under 3,000ft.lbs. as well, to keep the plate happy.