I'd recommend Blackhorn 209, with 90 grains to start, with a 250 grain bullet. If you're not getting the accuracy that you like at first, move up in 5 grain increments. Make sure to use CCI magnum primers, as they will burn the Blackhorn the best.
For bullets, I would recommend the Barnes SpitFire T-EZ's. They load really well, and they have great groupings out of pretty much every rifle. If you can't use a sabot, I would try the Barnes Thor, which is the same bullet, but without the sabot.
If you prefer to use pellets for powder, then just use 100 grains, and you should have decent groupings at 100 yards. It is very rare for someone not to have a decent group with 100 grains of powder. I recommend the loose powders like Blackhorn or Goex for dialing in your loads to shoot longer distances.
Good luck!