With a good barrel, well cut chamber, and the right bullet you can get a .38-55 to work very well with black powder. I think you'll find that the Shiloh will out do your other .38-55 rifles by a considerable margin, as long as you are using the right bullet with the right brass.
As an example here is a target I shot with my CPA at 223 yards. Of twelve shots ( including a cold bore fouling shot ), nine of them went into under a minute of angle at that distance.
Mind you, this was a breech seated bullet which, most of the time, has a higher accuracy potential.
https://www.assra.com/cgi-bin/yabb/Y...m=1451950847/5
Chris.