I'm trying to figure out just what this critter is!  It is marked Navy Arms - Ridgefield, NJ, made by Pedersoli.  The caliber is stamped as 50 Sharps.  A quick check on the chamber and it seems to be over 3" from the face of the breech to chamber step (max. case length?).  The sights are missing.  It has dovetails for the front and rear sights.  It has been drilled and tapped on the barrel for what appears to be scope mounting and the tang is drilled and tapped at approximately 1.5" hole spacing.
QUESTIONS:
1) What is the actual caliber? 
2) Where to get ammuntion, brass, bullets, load data, etc....
30 Sights: A Lyman 17 seems to fit the front OK, what's some sources for a rear tang sight?

Thanks in advance for you help,
Roger D.

SWAG would be one of the big Sharps cartridges.  The 50-140 is listed as having a case length of 3.25", so at 3", you've got a very slightly less obnoxious flinch-maker.  Buffalo Arms is the place to go for brass, dies, bullet molds, sights, etc.  The 50-140 is shown in the Accurate Arms Loading Guide if you want to run low pressure smokeless powder loads, otherwise you're looking at less than 70 shots per pound of black powder.  Have fun!

David
Montezuma, IA