To put a few actual figures to R'man's excellent post, an average chamber has a taper of about .005" per inch. Present SAAMI standards I believe call for a min dia at small end of .798". Now suppose you run a solid chamber gage of .798" dia into an old 2 5/8" (2.625") chamber which just happens to have a small end of not .798" but a whole 1/1000" (.001") under size @ .797" then that gauge will stop short by .001/.005 or .200", thus showing a chamber depth of 2.425". I do not concern myself with putting up "Proper Loads" in fold crimped 2 3/4" hulls as long as the chamber is at least 2 9/16" (65mm), the normal length of most nominal British 2½" chambers incidently, with cones of at least 3/8" length. The Brits have been doing it ever since the introduction of the fold crimp incidently.
Nota Bene (Note Well), though this does not mean off the shelf "SAAMI SPEC" 2 3/4" shells, the load "Needs" to be appropriate for the gun.
