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.