curt - This would be better asked in the blackpowder forum but I can probably help you out. When I had my inline, I called the manufacturer and he told me that although the rifle can easily handle a 150 grain charge, 100 gr is plenty. With 150 gr you will just be wasting powder.
And if the 100 gr charge is working for you that is plenty for deer or black bear with the 250 gr bullet. No, IMO, although the pellets are OK, you may be better served with the loose powder and a volumetric measurer. With these, you can adjust your powder in 10 or 5 grain increments until you find the most accurate charge for your rifle/bullet combo. Start with 80 gr of 777 and work up. I would say to no more than 110 or 120 grs.