With a set up like you have there, the best I can do at 50 yards from my Italian made .50 cal Hawken flintlock using 80gr 2F is having the shots hit within one inch of each other. But this is done after swabbing with a wet patch/dry patch between each shot. With muzzleloading, the key word is consistency. As for yardage? When I hunt with the flintlock, I like to keep shots under 75 yards, only because of limitations of the open sights.