Andy,
As brother
@necchi pointed out, almost everyone recommended .454” balls. There are reasons for that.
Cap and ball revolvers are supposed to be loaded with
soft, pure lead balls or bullets. With your experience hand loading for modern guns, you may have some knowledge of lead alloys for bullets. Put that aside. You need pure lead.
The reason for “shaving a ring” when you load is to demonstrate that the ball is achieving a complete circumferential seal within the chamber. Without that, you run the risk of chain fire, which is what we call it when chambers other than and in addition to the one you are shooting go off unintentionally. Fire from the chamber mouth goes in all directions when a round is fired, and if the balls don’t seal the adjacent chambers, the charges in those chambers can ignite. That’s why you want to use oversized balls… that and the fact that you need the ball to fully engage the rifling in the barrel.
One other thing… if you “mike” your chambers with a caliper, you are just about guaranteed an undersized measure. Depending on your skill, the error may be slight, but it can potentially be significant. If the caliper jaws are even
slightly canted or off center, your measure will be undersized. Even with the best technique, if the caliper jaws have flats on them, you will be measuring a small chord on the edge of the circumference of the chamber, resulting in an undersized measure. Your best option is to have the chambers measured with plug or pin gauges. Another option which is more work but avoids the cost of plug gauges is to slug the chambers. Remove the nipples and then load oversized pure lead balls without powder. Find a hardwood dowel or brass or aluminum rod that will slide in the nipple seat and use it as a drift to drive the slugs back out the front of your cylinder. Use a wood, plastic, or rawhide mallet for this. Then, mike your slugs. Getting an outside measure in this way will be much more accurate.
Or, just buy some .454” and .457” balls and shoot them.
Good luck!
Notchy Bob