BTW, it is unclear whether the gun is a 10 or 12 bore very similar to what was going on in this post:

http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=334170

The barrels are marked 12B and 13M (seemingly indicating a 12 bore), but a modern 12 gauge shell seems loose in the chamber (although it does seat properly).

Does anyone know anything about "oversize" 12 bore Greeners from this era?