BIB is correct. Going from .303 to .25 is a lot to neck down in one pass. Better to step down to .27 (as noted) and then .25. BIB is also correct, that this drastic of a neck down will work harden the necks, and they should be annealed before fire forming to the chamber.

While I am not an accomplished big bore shooter, I have spent quite a bit of time with sub-caliber wildcats and necking down many different calibers (some severely). Anneal, anneal, anneal...no sense in wasting your time making the brass, only to skip annealing and have the case necks split the first time...

I would think a .303 Redding bushing die would work well (just order the appropriate bushings to reduce the neck in different stages). Not real familiar with the shoulder position on this wildcat, so it may require a specific die to bump the shoulder back...

YMMV...