Patrick,
I own the Hofford barrel wall thickness tool. If operated correctly it will provide exact measurements time after time. If operated contrary to instructions it can provide inaccurate measurements. I believe those are usually larger than actual thickness.
Have you considered the buyer may have trying to make the barrels seem thin to reduce your sale price substantially? Little did know that just behind your friendly smile is a US Marine which when challenged, eliminates enemy though fire and maneuver. Or in that case, surely a glare from your eyes as sharp as a eagle focusing on ripping off a rabbits head! When caught off guard I instantly do the same.
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I think the bozo was simple a shister.
Mark