My best mix ever for .223 was a 50 grain Hornady SX and a butt-load of H335. I was shootin' high .3s with a Ruger 77 Mk II RL and a 2.5-8X Leupold.
If you can get Varget or Win 748 they should be worth a try. You might want to try something like the Sierra 52 grain HPBT. Sometimes changing primers makes a huge difference. So can playing with OAL.
Are you using new brass or once fired? I had one rifle (not a .223) that wouldn't shoot better than maybe 2.5 MOA with new cases, but the same loads in once fired brass from it's chamber went half inch or better.
Factory rifle accuracy is a needle in a haystack search. The search with a rebarreled, properly assembled rifle is not guaranteed easy but often more predictable such that a more methodical approach gives satisfying results.
Not .223, but I had a 700 LVSF .22-250. That POS would not shoot under 1.5 MOA with anything I tried 'til I got aggressive and ran 37.5 grains of Varget under a 50 grain SX. 1 to 2.5 grains over max depending on your book. Quarter inch 5 shot groups. WTF? Go figure. Them thar primers were FLAT. Anything downrange got an a$$ beating and it's guts scattered.
Y' just never know what's going to work.
Tom
