Brian Rothhammer
AH fanatic
I checked into how my Hornady 9.3X57 seat die worked with 300gr 375s in a 375 case (reformed 30’06) and it worked perfectly so I think you could simply do as you are thinking and give the 9.3 dies a try with a .375 expander.
The 9.3 has a lower, narrower shoulder and more taper as well as a slightly wider base.
Plenty of room for things to go wrong.
For my money I'd wait for proper 9.5X57 dies.
9X56MS, 9.3X57, 9.5X57MS
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