Need info on a manhatten Arms 12 gage, Barrel marked Fine Damascus, receiver side plate and barrel is engraved.

Manhattan Firearms Co. was principally noted for making pistols when it started out. (It wanted to capitalize on Samuel Colt's patent on the revolver scheduled to expire in 1856-1857)- a rather dubious beginning for a company that apparently started out as a bunch of quick money opportunists trying to cash in. I have never seen a shotgun with that company's name but I would urge you to get expert advice because bad beginnings can often be the source of real gold and this piece of yours sounds like a real relic of yesterday that can be worth real money to you. (The side plate engraving does impress me as indicating a shotgun sold to people with money)

Pictures?