Cayugad as always is right on. Many moons ago when PA started a muzzleloader season you could only use flintlock and patched round ball. There were a few lymans around with a 1:66 twist but most of us had 50 cal T/C Hawkens or Renegades wit a 1:48 twist. And we did pretty good. We used to go out on Sunday afternoons and put plastic spoons, handle first, into the edges of cardboard boxes and shoot off hand at them at 50 yds. We hit them with much regularity too. And several of us managed to get deer with them too.
But as Cayugad suggests you are going to have to play around with your rifle and see what it likes. Try different bullets with different powders and different charges. Sooner or later you are going to find the 'magical mix' of bullet and powder for your rifle. Good luck.