I'm no weapons expert, but, if this was cut down as a training example...why take the time to shape the front of the stock like that? It has many marks on it like it was tooled by hand.
Were these not typically made from walnut? To shape walnut like that would be a serious pain in the ass. It looks like it has been shaped for the other hand, so it would have been held by two hands. I agree that holding this like a pistol would have seen nothing but broken wrists and thumbs.
Could this have not been hip fired with the .410 shotgun shells?
I'm just guessing.
..and I have to say, this is one interesting discussion here