I am not exactly sure just how much length you can get away with. But on Ammoguide it says the 338-300WSM has 79.9 grains of water capacity.
The 338 Ruger compact magnum only has 69.4.
I think that if one could determine what max length possible for short action you might be able to get very creative in forming your own brass, but I doubt you will get much better than the 300wsm as parent cartridge....
The Wyatt is too long but it's parent cartidge is the 416 Rigby. I little more diameter. Perhaps shortening the 416 to the maximum length and necking it to 338. But may be more than action can handle. Thats why I will probably never wildcat something original. I know enough to be dangerous, not enough to actually know what my limits are