Jim,
the name "Suhl" rifle is not suitable to make any identification. Suhl is a town in Thuringia/Germany and was a kind of gun making centre during the 19th century (and in some instance till today), comparable perhaps with Liege. The stamp Suhl is found on many very different military arms of the numerous German states, including Prussia. Accompanied is the stamp mostly with some abbreviations for the maker (for ex. SP & SR for Spangenberg and Sauer). Most common Suhl guns in the CW are the Prussian models M 1809 (converted from flintlock) and M 1839 (percussion), both smoothbore muskets. In 1855 Prussia did some of both models rifle with an adjustable rear sight; there may perhaps found some the way across the ocean. Another one is the German Navy musket (of the shortliving navy of the German Federation 1848-1853), a shorter version of the Prussian M 1839 (also smooth), beside this it is anchor marked with a double eagle (the Federation symbol) and the stamp "City of Philadelphia-A.Wuerfflein".All have large calibre 18,5- 18,9 mm. You see, the .54 Lorenz rifle musket was far better than these "Pumpkin-slingers" and I guess Your gg-grandfather and uncles were happy to lay them apart. There are of course a lot of other Suhl guns,describing them would explode this mail. What I meaned with the M 1861 Suhl is the US M 1861 rifle musket, .58cal. Some were really produced by C.H.Funk, Suhl, Germany.
Best regards, Marc