I believe that's a British Tower.
definitely not a Tower gun with Suhl on the lockplate and a Charleville style nosecap. It is not inconcievable that it was used in the US civil war because both the north and the south had buyers in Europe looking for anything that would shoot
cheers mooncoon
Looks like a Prussian M1809/39 with barrel shortened 4". Large numbers bought by USA/CSA 1861-2.



























