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300 norma mag

Thank you. What measurement did you get with a loaded round? I'm getting .340?

If your loaded rounds are measuring .340 consistently, just get a couple bushings like .337, .338, .339. They're not super expensive and this way you can:
A) experiment with the the bushings and determine the best neck tension for yourself
B) be prepared if you ever notice your loaded rounds measuring slightly different.

Also it leaves you with the option of say, running the .337 bushing which will result in ~.003 neck tension, and then running them through an expander mandrel to open up the ID back to ~.002 neck tension.