My .45 GM barrels, most accurate loads are .0235" railroad ticking patch(mattress), a .445" cast ball and 75gr. 3F GOEX or 85gr. 2F GOEX. Identical shooting- only at 50 meters - I haven't shot it at 100meters - yet. Held well on a 4" black bullseye & double bagged, I've managed 1/2" (some better) 5 shot groups with these loads at 50 meters. I have no reason to believe they will not hold 1 1/2 to 2 MOA at 100meters in good conditions - without wind, off bags.
When using heavy powder, high velocity loads in any rifle with patched round balls, the load MUST be larger in diameter (as measured) than the groove diameter of the rifle, OR - the load will not provide it's best accuracy. That is what I've found in my testing and what all the ACCURACY shooters have found in their rifles as well. Find me a chunk-gun or BR shooter who uses only his thumb to start the ball and that will be the picture of a shooter who has never won a match - nor even placed unless he was only 1 of 3 shooting.
Guess I feel quite strongly about this - that's who I am. No offense meant. These are the facts for accurate shooting at the longer ranges.