Thought I may put my .02 in afterall, Round Ball shooting is a passion with some of us.
I also like the .570 rb, and I use a .015 (compressed) patch in my 1861 Colt Musket with a 1:72 twist. The gun really likes a round ball, and does quite well out to 100. Even better than my Penn Hunter in .50 cal with a 1:66 twist.
Most of my patch lube is done using BeesWax, and Mutton. I've tried several homebrewed concoctions, and most seem to work pretty well. I have never used Bore Butter, or T/C 1000....I probably would if I had it on hand, Most users don't complain about them, but I honestly can't say anything one way or the other.
I "probably" prefer a minie in the .58 Musket, when I can get one shooting just right. Right now I'm playing with a 575213 Parker Hale that is showing promise,I just wish it was .578 instead of .575. I believe it would do better. However, the minies do kick a heck of a lot more. and that makes the round ball a little dream to shoot. Some may even say "it's the only way to go".....Can you hear me now rollinb?
The whole secret, if such can be said, to shooting a round ball....with about any "reasonable" diameter, is a tight fitting patch. You don't want it so tight you have to pound on it to get it down, but you do want a slight resistance when pushing it home with the ramrod. That's it! Just push it down, good and firm, on top of the powder. Some say "don't bounce the rod off the ball once it's down", and others say it's okay. You be the judge. I'm of the opinion the bouncing rod thing does nothing except perhaps "pinch" a bit of patch into the ball causing it to hang on a little longer and perhaps destroying the groups. I don't know, but, I don't bounce. Seems this is something everybody has to work out for themself.
Russ