Hard to say. I would think that if the concern about cracking the action bar were valid, then it shouldn't have been rebarreled to .308 Win to begin with.

I would be more concerned about having adequate barrel wall thickness after reboring to 9.3. I've seen several early .303 doubles that had been rebored, rechambered, and reproved to 9.3X74R in England. I wouldn't have thought that an original .303 double would have enough meat in the barrels to go to 9.3, but these apparently did.
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