Mid 19th century based on it's shape would be my guess.
Fullstock, Congrat's to you on one very nice relic. I found one almost exactly the same as the one you found. The one I found had the little brass slide cover for the lock frozen in place of course. Barely seen on the front of the little cover is stamped U.S. I did some research and found this to be a CW period piece. I found my lock behind an old church that was used as a hospital by both armies during the CW. Your lock appears to be of the same period, in nice shape too. Well Done.