The Texan series of cartridges all use the 375 RUM cases because they can be necked down to form a donut to head space off of instead of seating the bullet against the lands or using the COW method saving one loading and finish fireforming in just one shot with very good accuracy while fireforming (I hunt with them while fire forming and they are consistently around 1/2 MOA while fire forming
The 30 Texan and the 7mm Texan both require the parent case to be expanded to one caliber larger and then necked back down to the original caliber for ease of chambering with proper head space. The donut also supports/holds the loaded cartridge with zero head space, like the Ackley cartridges do to minimize case growth and seal the chamber during firing.
All the RUM cases are the same volume except the 338 RUM so the 375 Rum cases cover the 338 Texan, 358 Texan the soon to be 375 Texan and the 416 Texan. The 7 mm RUM and the 300 RUM Are better for the 7mm and the 30 Texan sizing process. Increasing the case capacity by up to 20 grains requires different processes for the different Texan's so choices were made to use the different cases for some of the Texan's for ease of sizing.
Originally I tried the 375 RUM case for the 30 Texan but found the process work hardened the case to the point of collapsing the shoulders and annealing before sizing/forming the cases increased the chances of collapsing the shoulders so the decision was made to do the annealing after the case was formed for fire forming.
J E CUSTOM