Knights are all good rifles by all accounts, so I wouldn't worry from that aspect. You will get about 100 different thoughts on the powder thing, so I'd see what's available in your area and what works for your gun. I've had good accuracy from Pyrodex R and P and select, American Pioneer and Jim Shockey's Gold, 777 but after trying all the subs I'm back to just using Goex FFFg in mine.
Any muzzle loader can shoot round balls, so don't be told otherwise, it's just a matter of how fast. Most fast twist cannot shoot it with more than 60 to 80 grains of powder without losing accuracy from stripping the ball through the rifling. In my fast twist I get 3" 100 yard groups with 80 gr. Goex FFFg. I personally like pure lead great plains bullets, but ballistically if you need to take longer shots and don't mind using them, the pointies usually win out, like the SST's etc. If you have a slower 1:66 or so twist, roundball does much better and can be pushed a little faster. I still use 80 gr. in my Hawkin 1/2 stock though because it's plenty of power for BP range.
