Your padlock appears to be a Wilson Bohannon US Lock made under an 1873 patent. It is pictured in an article by Robert Dix entitled “US Armed Forces Locks” in the Jan.-Mar. 2012 issue of Journal of Lock Collecting. You can contact Mr. Dix through his email address dixlock@aol.com. If you are a new collector of locks, you may want to subscribe to the Journal.
Scott