Mr Berg, Welcome to TFL.
Can you please take a good photo of the lock side faceplate showing hammer, etc.? You stand a better chance of identification if there are any markings there or at least someone can note similarities with other percussion and/or modified actions in that manner.
and again, welcome. A lot of people here know a lot of useful information (I'm not one of them mind you
A free people ought not only to be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government." - George Washington, January 8, 1790, First State of the Union Address