update: My Standard AR10 rifle likes 168 grain BTHP. I shoot mostly reloads, over M80 Brass with 42 grains of Reloader 15. For store bought, I reserve the M118LR, because it is pretty hot, but it works well. So does FGMM 175 BTHP.
My AR10T likes a diet of 175 grain Sierra BTHP over 41 grains of RE15, in M118 brass and it also likes Lake City M118LR.
I shoot a lot of M80 surplus in both just to get the brass for reloading. Definitely notice the degradation in accuracy when I do.
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