Ditch the powerbelts and FFF powder. I have done extensive personal testing with different loads and bullets with the T/C Triumph, this is what I have found. 250 grain Barnes TSX bullets with 90 grains of Triple 7 Loose (not the pellets) is ideal. I have been able to maintain 1.5" groups at 150 (what I have sited in for) and good groups out to 300 yards. I personally took and antelope at 320 yards with this setup, although I would not condone this without lots of practice.
I tried the powerbelts at first, they just do not shoot well in this rifle, at least not anything close to what else is out there. If you must due to law shoot bore sized, try the other brands, Hornady FPD might be worth a try. They just did not fit snug enough in the barrel, imho, to shoot accurately.
Another powder worth considering, as I did like this one also, is Black horn 209. Close toss up between this and Triple 7, easier to clean so worth considering.