I know this is an old thread. but my new favorite powder for my AR15 is AA2520. I taken to slinging heavy metal at critters now. 75 grain Hornady BTHP over 25.2 grains of AA2520 is may new favorite coyote load. If I'm hunting pigs I swap in the 75g grain Swift Scirroco II over the same load.
.308 Howa 1500 Varmint, EGW flat base, Medalist MkII stock
.223 Howa 1500 Varmint, EGW flat base, Medalist 6655 stock
RRA 20" predator pursuit, Magpul PRS, Vortex 6.5-20X44MM, SWFA SSALT Mount, ALG trigger.