Each barrel is a bit different, I suggest that finding the sabot that matches the bullets to your barrel is the first and most important step.
Mine shoots many bullets well with the short [under 300 grain] black Harvester sabot. You should be able to tell a lot by just pushing the bullet and sabot through the barrel with the BP out to easy or to hard to push through wont shoot well.
What mine shoots well in bullets.
Shock Waves SST gold dot or Deep Curl and my hunting bullets are the Lehigh Bloodline all in 250 grain the 275 gr. shoot well to if you are after elk or larger game.
I also use the 50 /40 sabot and the 200 grain Shock Wave and the 200grain Lehigh bullets they are very flat shooting and do a good job on deer.
As for powder I use Blackhorn exclusively in my inlines I usually start at 90 grains and go up the groups will tighten the start opening up when this happens I check my saved targets and go with the consistently tighter group load. They usually tighten up at about 110 or 115 grains which is as far as most go.