Try any 55gr FMJ over 27 to 28 gr WW 748. I wound up at 27.5gr for 3075 fps from a 20" 1:7 Colt HBAR, and 3050 fps in an EA-15 with 20" 1:9 bbl. Set OAL from 2.225" to 2.235"
The old standby for the Sierra S69 MatchKing is 25.0gr WW 748 (or a little more if you are carefull) at 2.240" to 2.250" OAL. I used this load in NRA High Power in the late eighties before the heavier bullets came around. It went subsonic by 600, but kicked some butt at 200 and 300 if you did your part.
24 gr AA 2520 under a Sierra 77 is a good long distance load for the appropriate twist rate bbls. OAL for the S77 should be about 2.255" to allow it to feed from mags. RE-15 and Varget also work well under the S77 at around 24gr's.
Make sure cases are sized for proper headspace in your rifle. Best accuracy will be had if cases are uniformly trimmed to 1.75" and then get the case mouth deburred and chamferred on the inside and outside. I recommend a Dillon taper crimp die to just snug the neck up. These simple case prep steps will generate a noticeably more accurate round with minimal extra effort compared to all of the other rigamarole you may hear.
If you use ready to load commercial 100% processed brass, I have found that the case mouth de-durring still helps give more consistent chrono results because the seating and crimp tension will be more uniform if the typical ridge left on commercial case mouths is beveled off.
As always, scrub 10-15% of the charge weight anyone recommends and work it up 2/10's at a time over a chrono. Your mileage may vary
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