I have a TC Firehawk that I bought new years ago. I have never been able to get it to shoot what I would call "good". The best I can do is about 3" group at 50yds. Less powder shoots better for me. I use 80gr of cleanshot powder, hornady sabots with .44 cal bullets. If I go up to 100gr the group is twice as big. I've tried patched round balls, maxiballs, maxi hunters, TC sabots, buffalo bullets. Nothing shoots "good" for me. I consider it a 50yd gun and hope I don't have to use it. Fortunately most years I don't, that's why I haven't gotten rid of it. This gun is has the twist for sabot bullets so that's what I have worked with the most, I hate it, I traded my .54 Hawken that would take out the 1" circle in the target at 50yds with 3 shots because I wanted a gun that didn't look stupid with a scope. Wish I had the Hawken back. You'll have a hard time finding .54 cal powder pellets, I've heard they have them but could never find any. I went to the clean shot powder because it shot as good as anything and really does "shoot clean". Someday I'll get a different muzzle loader, but I do like the way the firehawk carries. I've also wanted to get the 209 conversion for it, but haven't yet. Good luck.
For my 3006 I use 165gr nosler partions, I reload my own, but you can get them in the federal premiums. Do some research, 165gr is going to do everything you need it to, especially with a premium bullet. People are going to tell you you need at least 180s or even 200s, not so, check a ballistics chart, 165 is going faster and hits harder. Busting brush with a bigger bullet, no such thing, do some research.