You're doing fine Yogi000. I'm glad you're having success with my methods or suggestions.
: The shot/cup base is excellent in holding the ball centred, seated cup-up underneath the ball - spot-on.
: 40 points of choke which is the old designation for standard full choke brings the full choke diameter to .689" from .729". Many full choke shotguns measure an even .690", while .702" is improved modified, .715" Modified, etc.
: Lyman and now Lee both have .690" round ball moulds due to this normal full choke size. Lyman even has loading data in their shotshell manuals for loading this .690" ball and other projectiles too, along with wad recommendations and different hulls and primers being used.
: Any side by side can be made to shoot accurately with round balls, however, one tube might not shoot in line with the other. You absoltuely need sights, a front and a rear that give a good sight picture. Once one has one tube shooting perfectly, great groups, in line with the rib, etc, tweeking that load can sometimes bring the other tube in. Juggling loads (if you are capable and understand what you are up to) can be effective in regulating the loads so the barrels shoot together.
: Use of the cup underneath the ball, holds it in the centre as it travels down the bore due to the "G" force of accelleration. It matters not if the bore is modified, full or cylinder. The ball is held centred. My double allowed me roughly 10" at 100 meters, 2 lefts and 2 rights, using a .684" ball at 1,550fps in it's cylinder bored .725" tubes. It was tight for a 12, while many today are way oversize. With a modern gun that is 'back-bored' to, say, .735", be aware that Lyman sells a .735" mould that casts around 600gr. in WW metal. I don't know if the doubles are 'bck-bored' or if that's only in pumps and autos. Lyman also sells, or used to sell a .715" mould. Currently, they have a .690", like Lee, for loading ball loads in 12 bore shells for an gauge shotgun.