This is a post-war farm grade shotgun put together from parts. Bridesburg only delivered M-1861 muskets in 1862. The hammer and barrel are am-1863. These mixed parts exist because of the interchangeability of parts. I can't see from the photo whether there is a band spring, or not, so it is hard to tell any more. I will respectfully disagree with Johan's assessment of the only value being in the sum total of the parts. That is correct regarding sales, but I see another value in this arm, which is as a representative piece of American History that shows the end use of thousands of ACW muskets. A number of well known gunsmiths also converted muskets into high grade fowling pieces! These cut-downs were sold also commercially by the likes of Sears & Roebucks and Woolworth's well after the turn of the century. They stayed in use on the farms for quite a few years. So many of these arms have been cannibalized for parts that they are now no longer common to find. All of this is why I feel they deserve a place in a Civil War arms collections. Just my thoughts on cut-down muskets!
J.