That T/C .50 Black Mountain Magnum has a 1 in 28" twist rate. It should be able to shoot Maxi-Balls or Maxi-Hunters. I would definately be using Goex FFG real black powder to start with. Much more positve ignition than any of the BP substitutes. I would also start my loads at 80 grains, and work up, in 5 grain increments. Also IMHO loads over 100 grains in a sidelock are a waste of powder, as accuracy is more than likely to decrease. I would try a .50 T/C Maxi-Ball, 370 grain or Maxi-Hunter 350 grain, are also good. T/C says a felt wad (Bore Button) over the powder in fast twist barrels increases accuracy when using Maxi-Balls/Maxi-Hunters, but I have had good results without one. Oh, and Yes, Maxi-Balls/Hunters, are good deer killers. Good luck.