I found such a cartridge, dummy. 20x110 RB, steel monolith inserted in a shortened case. In the place of the primer, screw. Additionally 3cm above the bottom, one crimp.
HS - 12 oclock - 1942
8 oclock - Oe Z
4 oclock - R G
I have found nothing about such a construction. Case typical Oerlikon, British, but the whole is unusual for me.
Does anyone have any idea for this?