I run 24 gr of R 15 in Nosler (Norma) brass, Fed SRmatch primer with the Hornady 75 ELD-M. My COL is set and tested for my load/rifle, so it will be useless to you, but it is in the ballpark of Hornady data for your bullet. DO NOT LOAD THIS BULLET TO 2.26 AR magazine length. I don't have any benchrest targets with pretty groups, but I do have a couple of 600 yard cleans with 10 or more Xs. This load shoots through a RRA NM AR with a 1:8 barrel, it should do well in yours. On a good wind day, it's boring to punch 10s at 600 yards prone. On a bad wind day, I feel it performs better than the various 80gr HPBTs out there.
If you do not have R15, I would consider Varget, H or I 4895, I 4064 to be strong possibilities. Some of the ball powders might get you there such as BL-C2, CFE223, W748, or even H335.