We size 9mm to .356
THIS ..... I use .358, for my S&W .357 .....
It comes back to slugging your barrels. How many barrels do you have to slug? .375 muzzle loader balls work well or appropriately sized fishing barrel weights. I can send you some balls, if you need them.
^^^I'm thinking about a new Sig. line??...HA HA HA..
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So maybe better get 2 dies .356 for 9s and .358 for .357 was hopping one die would the job.
I've got your balls...