I have never had much luck with the Hornady oal tool. Measurements were always inconsistent and never inspired confidence.

My recommendation is to make a dummy round (no powder and no primer) that has the bullit loaded long, long enough that you know it will not chamber. remove firing pin and ejector from your bolt.

Now you can incrimenaly seat the bullit deeper until it Chambers without resistance. I have had repeatable results to .001".

This technique is much easier if you have a micrometer bullit seater but can be done without.

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