When I got my White Oak Upper, (20 in. 1:7) John recommended WW brass and 24.1 grs to 24.4 grs of R-15 for both 77 SMKs (200 & 300) and 80 SMKs (600 & 1000 yards).
I went with that and it works quite well for me. I've played with other bullets but keep coming back to these.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071