A:
It would be nice if different diameters were offered in the other calibers.
Just like modern guns, you need to find out what shoots best with your gun. It would be wise to try diiferent diameters of round ball, different thickness of patching material as well as different amounts of powder. I have been hunting with a .54 cal flintlock for 15 yrs now. To date I get the best groups with a .530 ball, 70 grains of black powder (a traditionalist) and .16 patch.
Try both balls and vary your patch thickness and grains of powder. You can shoot all day and it won't cost you much. Shoot (2) 5 shot groups of each and find out which does best with your gun. Be mindful of ball and patch thickness. The greater they are the harder to load without cleaning. Good luck and have fun.