Different caliber, but here is a big clue, a .44 Hawes with similar markings, pretty nifty looking, assuming the old finish was intentional. It is at $101 on Gunbroker with no reserve. How does the condition of your friend's gun compare"
http://www.gunbroker.com/Auction/Vie...Item=307534441
And here's a pair of unfired .36 cal ones, at what appears to me to be an unrealistic price unless they were made in Germany. Hawes had a lot of stuff from Germany but I don't know if any of it was percussion.
http://www.gunbroker.com/Auction/Vie...Item=307807209
In the try-to-be-positive sense, if the one you're looking at will fire OK and is dirt-cheap and if you have a club with BP shooters and if you can buy a small quantity of ball ammo and pay the other shooters more than cost for the remaining supplies (powder, wads, caps) for a nominal number of rounds to fire, you can decide whether you are going to like BP before laying out a lot of money for the equipment and supplies you'd need.
This past year I bought a 1970s Italian .44 Magnum that was in similar condition to what you described, minus a base pin, for $50. The base pin will cost me $30 delivered. I figure the gun then will be worth just about the $80 I have in it.
There are a few posters here who know way more than I do about these, but I suspect they are going to tell you that this is not a Rembrandt at a garage sale. Didn't want you to feel too lonesome while waiting for an expert response, which mine is not.
If your friend will let you take the gun apart, look for either Uberti, Perdersoli or Pietta marked anywhere, including under the grips. If you see one of those, you might have a decent chance of finding replacement parts for the same model marketed under their own brand. Most good gunsmiths should be able to keep it running, but you have to question the total investment you want to risk having in this piece.