The British “trade” back in the day was very proprietary, so each maker often did something different. I guess not just to be “different” but to lock the customer in to buying the proprietary ammo for his rifle. Interesting, but does sometimes make it a challenge to source brass and dies once you suss out just what the rifle is really chambered for.
It comes to mind that the Lang designed .470 NE was a kind of exception as it was released to the trade so anyone could chamber for it.
- Mike