I have read, many times, that the 22-250 is merely the 250 Savage necked down with no other changes.
Then you've read wrong many times. Shoulder angles are different, datums are different lengths, etc. A quick review of most any load manual will confirm this. Cases formed from .22-250 hulls don't always chamber in .250-3000 rifles. Since Graf's, Lock, Stock & Barrel, Powder Valley, and others all currently stock .250-3000 brass, why are you even considering reforming from something else?