It was restocked by me and father mate you are right smile. The gun has an unusual ejector system ( at least for me ) which is called Deeley ejector Mechanism. And the pin in the back lump might have something to do with that since the ejector is working fine we didn't have the need to dissasemble it. that 13/1 is the bore diameter 719" but i don't have any idea when it was nitro proofed.