Pellets will not work in your gun unless you crush them at loading. Pellets are made for in-lines and some revolvers only. They are more expensive and less powerful than granular. Been there, tried that. Crushed one and dropped in # 2 and fired. #2 came out behind the bullet and looked like a roman candle.
Pyrodex can be a pain to shoot, however, run a patch and shoot a couple caps before loading will help or shoot a fouling shot (blank load). Duplex load with a couple of grains of Goex first will do wonders. Also a musket cap converter will give a hotter spark or a small rifle primer converter will also work. Winchester or Dixie makes hot magnum caps.
What are you trying to accomplish? My little group of mountain men have experimented with all sorts ideas for the past 30 years. Just ask.