Corey,
Absolutely the 378 Weatherby is based on the 416 Rigby. Yes they added a belt and the traditional Weatherby double radius shoulder, but the 416 Rigby case was the inspiration. This is common knowledge.
The 338 Norma brass has been going real well, lasting 20 loads at 65,000psi so far. I haven't been able to kill a case yet. And it has eliminated the expanding and full length turning then necking down again case forming steps. Now it is a simple neck down, shorten, neck turn, anneal and fireform with Shotgun powder.
Greg