Stevens New Model Pocket Shotgun No.39

Hello, this is my first post and I am trying to obtain some information about my Stevens New Model Pocket Shotgun No.39 "I think" that is the proper model............as this is what was told to me by a gentleman who is/was a Stevens collector and historian. I am going to proceed cautiously because there could be some issue about this gun which I shouldn't share until I know more. I guess it has to do with the caliber and the barrel. Here is what I know, or think I know.

My grandfather worked for Stevens eons ago and supposedly he made this gun. The collector slowly gathered some info from me and at the point I shared a few facts with him he said "I'm don't mean to be rude but that gun was never made in that caliber" I sent him pictures of the caliber stamp and informed him that my grandfather made it at which point he said "well if your grandfather made it, it may be a one-off"

Let's just say it looks a lot like this, physically, not condition. It is in a multi-fold felt-lined canvas pouch which holds the gun and stock.

This is a family heirloom and I would really like to put the endless stories to rest about exactly what it is.

https://live.amoskeagauction.com/ima...jpg?1578596525