Should the chamber be a bit undersize, not uncommon on older guns, & be only .001" smaller at the end than the diameter of the gage, the gauge will show it about .200" short, which it isn't.
Better check your math there. Or your source. I seems to remember another regular came up with this error when telling how to measure chambers with a machinist scale.
Well the Chamber of a shotgun has a taper of approximately .005" per inch. Therefore if the gage dia is .001" larger than the small end of the chamber it will stop short by .001"/.005" which = .200". I worked 35 years as a machinist & am quite familar with measuring things. I observed this by actual hands on experience, not Heresay. I had in fact built a set of chamber gauges for 12, 16 & 20ga guns, but after encountering this "Problem", I no longer use them much preferring my old Starrett 6" scale. If you see a problem with this math "PLEASE" do explain it, for I see none at all. I in fact once had to measure the end dia of a cone to very close tolerances. As I had bored the taper & knew the exact angle I did the measurement by building a plug to a known dia to fit the spindle of a depth Micrometer & then measured how far it would enter the cone. This was a matter of math & trig, but you don't need the trig to measure the length of a chamber. It is in fact quite Elementary.
