I haven't read every single post, but in scanning over this thread one factor I have not seen mentioned is that the caliber or bore size of any given barrel is the nominal size. Your .58 may not be .580". I have a CVA Big Bore Mountain Rifle which, as near as I can determine without unbreaching and slugging it, is about .572". The barrels from the now-defunct Green River Rifle Works were notoriously undersized. I have a Hawken John Bergman built for me around a NOS Green River barrel which was nominally .54 caliber, but appears closer to .53. These also had some choke built in, so it is even tighter than that near the muzzle.
I think you just have to try some different balls and patches and see what works. No need to fear shooting a smaller ball if it is hard to load, or a larger one if it feels too easy.
Notchy Bob
I think you just have to try some different balls and patches and see what works. No need to fear shooting a smaller ball if it is hard to load, or a larger one if it feels too easy.
Notchy Bob