That slotted key goes through a staple-looking protuberance affixed to the bottom of the barrel. Not really necessary with the Mauser system and its action screws. Kind of a "belts and suspenders" arrangement.
I'm surprised nobody commented about those early version of see-through mounts. Without altering the angle of the bolt handle to clear a low mounted scope, they had to use really high rings. I guess they figured since they were doing that they might as well put some peek-a-boo holes in them. Or maybe it was simply a tiny weight saving feature.
It would appear too that the trigger guard on Don's rifle started out as a military one with the sling hole in the leading edge that the gunsmith filed away to make it more svelte. I've done two like that and in the end the front of the trigger guard gets pretty thin. Compare that to the Krieghof below it which sports the commercial Mauser trigger guard.
Last edited by gnoahhh; 05/23/16.
