Thanks for posting. Like Claydog, this is the first time I have heard of these Brit cartridges.
While they look interesting and had possibility if the gun press had been supportive, they had a lot of much better supported comoitition and faded away.
Reading old gun magazines and Handloader's Digests, there are so many obscure potentially great cartridges including wildcats. Most shooters have never heard of say the 256, 30,or 35 Newtons which were great cartridges, lost in time. The list goes on and on.