I have an email in to them since Thursday(because of pictures), but I figured I might get lucky here before they get a chance to respond. I've been told it's original Krieghoff accessory from the 60's, but I always thought differently(for the reason Jim Watson gave) so the US part of Krieghoff might have to figure it out. We'll see what they say when/if they get back to me.
Thr maker seems to be a machinery company at this point, not sure they can help at all...but .22 mag would be latter half of the century I think.