It is called a riveting hammer. If you look in old tool and hardware catalogs you will see them listed. Some catalogs list them as being "Tinner's" riveting hammers. All the material missing from yours is also information missing. I would ask your friend where he found it and you could look up it's history and see what used to be there, maybe a farm or if a home was nearby you could see who used to live there and what they did for a living. If you are going to be collecting old tools you may as well start educating yourself and become your own expert. It is hard to date modern hammer types like this by material as cast steel and wrought iron both were in use all the way through the 19th century. Bessemer process steel was invented right before the civil war but it took WWII to end the general use of crucible/cast steels and wrought iron. Tools were expensive things through WWII and back in the day someone with the means and material may have made themselves a lot of the tools they needed instead of having to come up with money for manufactured ones. I have a lot of hand-made tools laying around here that are not that old, I am sure some of them are post WWII, but some are also definitely pre-1900, I am talking hammers, chisels, wrenches, and anything else you can imagine. So unless you can find a likely history of who threw or dropped your hammer where it was found, you may be out of luck.
