I will concur with Fede, this method of production was very much the standard on early cases. My understanding is that is was done as a means of ensuring a good fit of the cartridge in the chamber as at this time holding exact tolerances was “not” readily achievable, so the head was given an inner raised area (ring). This was the high point so that when the gun was shut with a maximum depth chamber flange the cartridge was at worst a slightly lose fit in the chamber but on a minimum depth the breech face would compress the rim and deflect the base enough that the gun would still close properly. It had a secondary use too, in that it helped to seal the cap chamber and to some extent stop the flash back onto the breech face and achieve a better gas tight seal.



Shown are a few variations of this on some Kynoch cases.
Whereas the Greener Police Gun had two pins that protruded from the breech face this would certainly stop the gun from closing on a standard headed cartridge but the Greener principle had a large grove in the cartridge head to allow the pins to fit into the face and therefor let the gun close.

With it being a grove the orientation of the cartridge didn’t matter either.