Although I've had the T/C .56cal. SB for a while (I got it "used," but essentially never fired), I never summoned the resolve to test it at anything beyond 25 yd. That changed today. Past experience has shown it to be accurate at 25 yd. when fed the proper combination of ball, patch, and OP wad. More about that in a bit. Btw, the gun hasn't enough drop to fit me, so offhand shooting is awkward, to say the least. Shooting from a rest, which I did today, is worse since the comb smacks me squarely in my face (cheek bone). I cured that by making a pattern and then cutting & sewing several layers of synthetic sheepskin to the stock: problem solved! Resting the gun exactly as I would when shooting offhand (front rest + rear bag), I managed to shoot a group that was 2 5/8" x 2 3/4" with 2 shots in essentially the same hole and 2 more touching. These were shots 3 to 7 as the first and second were foulers, which is something I want to bring up in the 3rd paragraph. In short, they were wide of 3 -> 7, but still on paper, but not the outer scoring ring (6 1/8" in diameter). As happy as I was with that rifle-like group, it was a bit to the right of center, and in trying to adjust the rear sight, messed things up a bit. A trip to the 25 yd, range with a fresh target (also 6 1/8" dia.) got things back to normal, with 3 shots in 7/8" (edge to edge) and one 3/4" away, also edge to edge.
The load I used today was 80gr. Diamondback FFg with a .550" ball cast from a Lyman mold. The OP wad was 1/4" thick wool felt that I cut prior to heading out to the range. Btw, the felt came from Duro-Felt, which is wonderful to deal with. I didn't have time to lube those wads today, but they work better with lube (I use 1 beeswax : 6 white Crisco): less breech fouling and no bunt wool stink! The patch is some tightly woven 100% cotton material similar to pocket drill that I picked up at Jo Ann Fabrics and mic's @ .010", compressed. As thin as it is, it is a tight fit with the .550" ball, but it has never burned through when I didn't use felt OP wads. The patch lube was 1 Ballistol : 6 H20.
In both my trade gun and the T/C Renegade SB I've noticed that I get tighter groups when I use an OP wad, either felt or cardboard, with a patched RB. I'm also finding that a slightly tighter ball - patch combination, though a bit harder to start, may positively effect accuracy albeit to a small degree. Lastly, having fired the trade gun last week and the Renegade today, I'm finding that it takes 2 - 4 shots for the bbl. to settle in and produce tighter groups. Has anyone else experienced this too? One last point, I read over on the Traditional ML Forum that the T/C .56cal. SB can produce "rifle like" accuracy with a .535" RB and an appropriately thicker patch. Maybe in some guns, but trust me, not in mine. I tried it several times with a .535" (.537" in fact) RB + a .022" and .024" denim patch + OP wad with the same 80gr. charge mentioned earlier: No dice! The smaller ball + thicker patch resulted in groups at least 50% larger than the .550" ball + .010" patch I'll continue to use.
Hope this gives you smoothbore shooters some heart: Those guns can group!