The Birminham proof marks on the barrels were in use from 1813 to 1855. The general look of the gun suggests it was made in the latter part of that period.
An interesting fact which was uncovered while researching this gun was that contemporay literature of the time talks of "lefts and rights" instead of "rights and lefts" pertaining to which barrel was fired first. That answered my question of why the cavity of the left hammer that struck the cap, on guns of that time, are more beat up than the right. Before finding that out, I found it was more confortable to pull the left trigger first, on the gun I had used on gobblers, so there really was a purpose in the way the length of pull and trigger set up was designed.
I am ordering some old catalogs from the site I posted above.
Bob, Please post some photos of your gun.
Ralph