You can use both, I prefer the pellets they are quick and painless but if powder is the way you want to go it will serve you well to. Remember to by the proper measure if you use powder because black powder is measured by volume and not weight.
Pellets or loose powder each has its good and bad points. Just remember to clean you rifle up each time you take it out shooting. Don/t leave iot for a week before you clean it up or the bore will pit. Hornady SSTs seem to shoot okay out of most TC rifles.