Surely, it's the belt around the cartridge that seats and obturates the cartridge in the chamber! Not that it's too important, but the headspace is calibrated from that point too. You couldn't fire-form the belt around the case, it's a solid ring isn't it? And if you did try, wouldn't it just bulge, stretch and break or at least form a critically weak ring of brass. I'm not an ammo man, just a simple engineer, Or am I over complicating this a tad? Anyone else out there........