Just a passing thought for folks that also get frustrated with measuring three groove bore diameters.
This may be common place for all I know.
Stand up a minie on a hard surface and tap the nose with a hammer. Try it in the bore. Keep tapping the nose until there is resistance from the the base going in the bore. With the bore oiled, hold the minie by the nose and turn it in the bore. Tap it again. Twist it again. Keep going. After a while you get a shiny band of lead on the base of the minie that you can measure. The way that I do it (careful tapping and twisting technique, my hammer, my hand) I'll get right at 0.002" under the bore diameter. And, no longer have to borrow three point micrometers.
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