Without re-reading the whole thread - as far as I recal, nobody said it was 17 thou at 9" from the breech. Did they?

If it were the case, I would be unwilling to use the gun. As I said in my post, te thinnest part of the barrel will usually be what was always the thinnest part of the barrel.

The only reason to re-proof a gun is when it is technically out of proof.

Homelessjoe, you are missing the point. A gun either fails when it is proof tested or it does not. The Proof Master is not interested in the barrel thickness. A strong thin barrel at a 16 thou minimum may pass and aweak thich barrel with a minmum if 30 may fail. I have seen both.

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