My measuring ring set on the $495 Galazan bore gauge is "heat sinked" as purchased. You zero in the ring, measure the gun immediately after. I don't think I will experience a variation of more than .00001 that is related to temperature. I spent 5 1/2 years in an instrument shop in an earlier life, understand close tolerances, but measuring a shotgun bore is not rocket science and a thousandth or two does not change safety level or value. By the way, the $495 single head Galazan gauge (not the interchangeable head model) is the only gauge I am aware of on the gun market that will measure tens and eights. It's maximum measure seems to be .900, plenty for the biggest eight gauge bores. I have not confirmed the accuracy of the .900 measurement, but will as soon as I can get an accurate zeroing ring at close to that dimension.
