HI John send me a picture of the shotgun hammer as I may have something that could work for you (no promises just a maybe). I also have a box of rimfire ammo that came with a similar Mauser, can't tell you the brand offhand but it is European and contemporary with the rifle. I need to get it out of my ammo collection and will take a few pictures, which may be a few weeks as reorganising the gunroom and currently buried. You are welcome to have the box/ammo should it be of any interest to you.

Steve