Yeah I have given up trying to push the boundaries with heavier bullets in the 223, the juice isn’t worth the squeeze
77 TMK and 73 ELDM are the sweet spot
I had good luck with 75 ELD-Ms and N140 but I never shot them past 400 so it's hard to say definitively that they are that great. When I run out of TMKs and my new mags get here I'll go back to them though.