An 80 grain boattail seated long and loaded single shot for slowfire prone at 600 yards pretty much rules the Highpower Service Rifle game. If you want to play Designated Marksman, a 77 gr at magazine length ain't bad.
A 90 grain .223 in a fast twist barrel has about the same trajectory and windage as a 175 gr .308; and is fun at 1000, if your target tender in the pit doesn't mind looking for the little bitty holes. Some folks find that difficult, resulting in slow pit service, so I just shoot the .308 at 1000 and save the .223 for 600 where there are plenty of others and nobody complains.