AR Hillbilly,
Good Morning. I second Hawg on that. Definitely .454 ball. When you drive it home into the cylinder it should leave a a small ring of residual lead on the top of the cylinder thus assurring a very snug fit. There are some who prfer a .457 round ball (of late difficult to find). I have never used them but some swear by them. Obviously a little more force is needed to drive a .457 home. As far as the different larger nipple hole sizes? I'm not sure why that might have happened.
I will have to defer to others, like like Hawg, Shotgun Dave for a possible reason. Also, if by chance you are not aware, avoid using any petroleum based cleaning and or lube products with you BP revolver. This can cause very bad fouling in a relatively short amount of time. I've never used Gun Scrubber so I don't know if it's petroleum based or not??
I use "Ballistol" myself. A non petroleum product. Some hate it and others swear by it. It's okay once you get past the smell they say.
Just make sure the cylinders and nipples are good and dry before you load your BP. Are you using a lubed wad or some type of filler? Good hearing from you AR and thanks for the questions and keep bringing them on. I wish you great luck on the range!! Man, I gotta tell ya, I am envious my friend.