Re: favorite Powder for 5.56 / 223 using 77 gr SMK
23.5 H4895
23.2 IMR 8208
24.5 Varget
24.0 RE15
24.5 N140
23.5 N135
That should get you started. Those are in order of accuracy for me in several rifles, the H4895 was best in everything. You can take it up to 24.0 as well as the 8208. Little warm in a 1/7.7 krieger CLE chambered AR, but wylde and NATO chambers were fine. With the 1/7.7 CLE 20 in the 23.5 H4895 gives me 2820fps and best accuracy over all. 24.0 matches Mk262 @ 2850fps and groups opened up very slightly. Do not use standard primers use a mil or mag that has a harder cup. The 8208 load for 24.0 is just as accurate as the 23.2 load and matches mk262 perfectly in the wylde and NATO chambers.
The Varget and RE15 loads are "standard" high power loads, just dirty and the Varget isn't very meter friendly for me, the RE15 is better.but dirtier. The N140 load is great just don't use that powder anymore. Pricey. The same for the N135
Hope this helps.