Tony and I built this (well, Tony did the work, I helped resolve the issue that led to the designation SOCOM-R)
The heavily rebated rim on the standard SOCOM case will not work with the T/C extractor. So if you use standard SOCOM brass, it became a system of "Shoot-Poke Empty Case Out With Cleaning Rod-Repeat As Necessary". That ain't no fun.
So we found that .50 Alaskan brass, formerly known as .348 Win brass, has the same base dimensions and the required length, but is Rimmed - now you have RIMMED .458 SOCOM cases, hence SOCOM-R .....
It uses the same dies, just a different shell holder. I have shot this particular hand cannon with Tony. With 500 gr subsonic loads and the 12" suppressor - a kitten. With 405 gr FN full house loads - Whoa Nelly!