2-Piper. Yes, it was just my crude way of trying to describe how the firing worked to prevent normal ammo being used. I also have some Mark I and Mark II cartridges but they are all brass and without the recess around the primer but of a two stage tapered design.

fallschirmjaeger, the case hardened ones seem to be the scarcest and out of the many GP's I've seen only a couple have been colour hardened so they may have more collector appeal. Lagopus.....