Have you got any pictures, particularly of the proofmarks? My books show August Friedrich Wilhelm Timner, of Coblenz, Germany, as having submitted a US patent for a breech-loading rifle design in 1875, but no info on any shotgun; you can see his patent at http://patft.uspto.gov/netahtml/PTO/srchnum.htm , if you enter 0165892 in the search box. Hope this helps.
