Apparently, some Brit guns (i;e;: 2" 12b guns) were built with barrels as thin as .018, sometimes less. So they were proofed and left the factory with barrels less than 20 thousandths of an inch. It all depends on the intended use and, of course, on passing proof spec for the cartridge designated.

As Jack Rowe states in his video, the measurement 9" from the muzzle is usually the thinnest, where the pressure has diminished significantly with a nitro cartridge. So, a gun might have .015" thickness at that point, or perhaps less, and still pass proof, but it would dent very easily and would not be thick enough to safely repair the dent.

My main 'smith, Pete Mazur, uses an ultrasound thickness detector. Interesting to watch - a lot like a medical ultra sound procedure.

C Man
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