Personaly, I liked whay one of the fellers said at the beggining and that was to measure the I.D. of the barrel. I know ya used a gauge, that's it, it's simply a gauge. I think they ment for you to use an inside micrometer to see what measures EXACTLY. Then you will KNOW what the I.D. truly is. I think (FWIW), that a gauge is only used to determine a neighborhood. Whereas a measuring tool will set it right in your lap.
My tupence worth.
h-a