I have a Centaure/Centennial 1860 Army that had 2 rusty cylinder chambers when I got it. I got a Pietta 1860 cylinder to replace the rusty one. It seems like it's almost a drop in fit. The notches on the Pietta cylinder are a little bit forward but they do just barely line up with the bolt and when I cock the gun the chambers seem to line up with the bore correctly. The only problem seems to be that it is a bit too long and when I try to put the barrel assembly on the forcing cone hits the cylinder face and leaves a small gap down at the frame pins.
It appears the only thing I need to do is sand down the cylinder face. The problem is I don't have a lathe so I would have to do this by hand. Is it feasible to just tape some sandpaper to something flat, like a piece of glass, place the cylinder face down on the sandpaper and grind it down by rotating the cylinder by hand? Is this likely to result in a non-square cylinder face?