When I first read the question, my reponses were "Alliant RELODER 15 and Hodgdon Varget". If you can't find one or the other of those, and your rifle won't print reasonable groups with 68-69gr bullets with one of them, I don't know what else to tell.
My one suggestion, and I hate to go counter to Lovesbeer's notes, because I agree otherwise, is to avoid 748 with heavy .223 bullets. Pierced primers result on warm ways with safe loads. Actually, I was piercing primers with 748 and 69gr bullets with loads that were only running 2600-2700 fps from my 20" AR. For reference, using Varget or RL 15 I can hit 2800 with ease with the same bullet and not burn my firing pin and bolt face. 748 is just too spooky on hot days for my tastes.