RE: 12 gauge. round ball loads
While true the bore of the 12 is .725 - .730 depending on who you ask. So I am guessing the .690 ball with a thick patch would work just fine. I shoot a .62 smoothbore and shoot a .600-.610 ball with a patch and it is accurate enough for me out to about 45 yard. After that I kind of loose faith in the accuracy, but I have a few more idea I want to try to see if I can stretch that distance a little.