I have been meaning to make a wall thickness measuring tool for some time, but have had the use of a Hosford when ever I wanted, so just never got to it.
I like the Hosford design because it eliminates the deflection error.
I will probably make mine like Tom's; a vertical pair of rods. I have seen commercially made vertical devices which have a tapered bushing which keeps the muzzle centered. The key is that the dial indicator have enough pressure to hold the barrel against the reference point. I was wandering around Harbor freight one day, and despite my resistance to not buy Chinese, I succumbed to the $15 digital electronic inch/metric dial (sic) indicator. The floating zero is a great feature. That way you have a direct wall thickness reading.
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