Dean, It seems hard to get an exact measurement from one of these gauges when you are holding one end with your hand and guiding it through the barrels. seems the chance of moving the gauge inadvertently up or down or sideways would skew the results, also seems the weight of the arm albeit very small would make a couple thousands difference. It seems you would need a "guide to put in the muzzle end of the barrel to keep it in the center and give a much more accurate read and not be subject to hand movement, but I do not own one of these gauges so have just seen them demonstrated at Deep River, Gary
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