Interesting note, Dan.
My .58 Zouave(Armi-San-Polo?), back in the 70's shot very well with patched round balls, but it needed 100gr. 2f to do shoot well enough to satisfy me. I did shoot mostly at 100yards, but now and then shot closer, ie: 50 yards. I used .575" balls and .022" 'brushed' denim patches with spit or Marmot Oil for lube.
Through the 70's, I'd worked up loads (and altered sights) for several guys who had the new Parker Hale Enfields, both 2 band rifles and the 3 band rifles, with .575" round balls and denim for patches. Snug going in, clean and accurate shooting coming out. One guy in particular, with a 2 band Enfield, was able to shoot several 2" 5 shot groups offhand at 50yards, back to back, when testing that rifle as I'd altered and developed the loads. He was quite happy with it.
My current Musketoon, with 24" bl. has a .574" bore and I found the .575's just a bit too snug so tried my .570 Lyman mould, which cast a .574"X.573" ball. Those too needed to much effort so now I use a DC Lee mould that casts .562"X.562"- same denim or heavy ticking patch. 3" for 5 shots at 100 meters off the bags is fair for such a short barreled rifle and 'fightin' sights.
I think if you give the military-type .58's a good test with different components, you'll find they are GREAT round ball shooters- even the Enfields with progressive depth rifling like mine. Incidentally, they badly need a nicely radiused and smoothed crown or you will NOT be able to start the patched ball without cutting the patch.
