z Sold ~ Puzzling? Nickel plated 1851 with no marks

NICKEL PLATED 1851 NAVY NO MARKS OF ANY KIND. No manufactures name, no proof marks, does not say "Blackpowder only",and the cylinder has no naval scene.  No serial number. My instincts say this is very early import before all those marking were required. The hammer, cylinder, frame, barrel and loading leaver are all nickel plated. I believe the nickel is either factory or professorially done. The screws are all blue and in perfect shape. The grip frame is brass with no nickel finish? The grip look and finish is that of a factory done gun. The chambers, nipples and bore are unfired. The right side of the barrel and cylinder indicate this 51 was stored in a holster for a long time causing them to show moisture damage to the nickel. This gun is mechanically perfect.  This gun makes me wonder where it came from. Was it a kit gun nicely done by a professional?  Was it a factory prototype?