The 250 Savage, and the 250-3000 Savage is the very same cartridge.
The 250-3000 is the "mother case" for the 22-250...
... but there is no "mother case" for the 250-3000.
While "theoretically" you can make the 250-3000 case from 30-06 or 308, it is such a pain-in-the-azz, that I'm sure you can find better things to do with your time.