Difference from the diameter at chamber end of a standard chamber to a bore of nominal diameter is about .070". Thus the cone tapers down by that .070" over its length. The chamber body itself has a nominal taper of about .005" per inch (can be slightly less) so a 2˝" chamber has a taper of .0125" over its length, a 2 3/4" chamber has .01375" & a 3" chamber .015" of taper. On any of these if you insert two plugs having a difference in dia of .001", assuming both fall between the small & large dis's of the taper they will stop .200" apart.
As can be seen there is little likelyhood of reading a short chamber to be a longer one as Larry stated. There is indeed a great likelyhood of reading a chamber to be short when it is in reality only a thousandths or so undersize. This will present a problem in chambering "Only" in the case of a shell measuring right on maximum. I have never encountered any modern hulls which do, in fact most run well below maximum. I have had several guns over the years that a chamber gage built to minimum chamber dia would show to be short when they in fact were not, only small. Never had a problem with a single one of them chambering a shell. These guns were pre SAAMI guns, which of course are also the ones with un-marked chamber lengths.
