The gun that comes to mind is a hammer double owned by a friend's grandfather. It had seen very hard times and was missing the underbolt that slides into the lump as well as the greener cross bolt. It was held shut by a large nail on a string (so you didn't lose the nail). He had lost one hammer screw so held that on with brazing and the little tit on the mainspring had broken off so the mainspring was welded to the sideplate. He had also bound a wooden rib to the top of the barrels (with string) and soldered a sheet metal (read bean tin) rifle type sight to the back of the barrels.
He apparently was an avid hunter and I am under the impression that he shot the gun a lot prior to his death of old age.

cheers Doug