doesn't also depend on how deep the rifling is in the barrel? My Lyman has fairly deep rifling and it is pritty tight with a .490 ball and 18thou blue pillow ticking and pritty darn accurate for how small the barrel is
Depending on the groove depth and land width, some times a slightly smaller ball does better. At 25 yds offhand, whether you shoot a 487 vs 490 vs 495 really matters very little for 99 % of shooters. Some rifling is a little "tighter" than other and it may be easier to use a smaller ball, or thinner patch. In my shooting, the target pretty much has to be 75 yds or more, before the patch ball combo makes a significant difference.
All depends on how the bore is cut on the barrel.I have a 36 cal that likes a .360 ball and a .010 patch and one of my 45's likes a .451 ball and a .015 patch.I have tried .455 in this one and its not too tight.Just another varible to try in the never ending quest for accuracy!