In general because all rifles are different, the optimum sabot/bullet size for 1-28"s appears to be 300 grains for barrel sizes 22" to 28" -- yardageranges between 50 & 100 yards. A majority of 28s will shoot any sabot well with the right powder/primer/dry barrelload from 180-400 grains real well - if the rifle is solidly constructed.

Conicals are different thou. I'm assuming you are shooting sabots - so I'll end the discussion here.