I've always looked at the case gauges to be maybe useful for pistols, but that's likely about all. Chamber is cut with one reamer, die is cut with another, then the case gauge is cut with another reamer again. All cut to "SAAMI" specs---and tolerances, with reamers that are how new, how old, spec'd to cut which side of the SAAMI spec tolerances. Seen a number of cases where the issue, was just with the gauge they had, and just the wrong combination of the tolerances. Very convenient, nice product, when it's sized right for the die and gun combo. I've always looked at it as a gimmick.