I normally use pre-cut patches from either T/C or Traditions, and if not pre-lubed, I use wonder lube on them. I have had great success with these combinations with a .490 RB in my .50 cal T/C Renegade. I also have a combination I use for target shooting that uses an Ox-yoke pillow ticking patch with a .495 RB. This combination is a bit too tight for use in the field, and requires the use of a stout range rod to seat the ball. The above combinations I use for .490 RB are tight, but still easily loaded in the field with the original style wooden ramrod. The T/C patches I use mike out at approx .020, and work very well with a .490 RB.
I know that by playing around with different patches and powder charges you should get better than 5 inch groups off a bench at 75 yards. At least that's been my experience with older T/C muzzleloaders.
Maxi-balls can also be wicked accurate in these rifles as well, so you might want to give those a try as well. Casting your own projectiles will save a lot of the cost of shooting as well.