Re: 300 winn mag to 257 stw
I've got a Savage long action Tactical that I had rechambered from 7mm Rem Mag to 7mm STW. The smith ground back the bolt stop to allow the bolt to travel a little farther back and spliced two internal mag boxes together to make a new mag. That plus a new follower made a nice 7 STW. The action is plenty long enough for an STW.
The critters have to win every time, I only have to win once.
NRA Life Member