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Here is some actual data from a Finnish Mosin instrumented with a strain gauge. The standard deviation of the random error in that particular system has been measured at 335 PSI, which is practically the same as a good piezoelectric system. The case head measurements were made with a Mitotoyu blade micrometer, clamped to a granite inspection block to ensure that all measurements were made at the same height on the case head. Since cartridge cases are not perfectly round, three measurements were made on each case at different orientations, and the three measurements were averaged.

The brass was all from the same batch, having been fired once.

Note that there are two rounds that were over 60 KPSI that measured .0001" or less of case head expansion. If you follow the 95% PI intervals across the chart, .0003" represents something between 49 KPSI and 75 KPSI. Close enough for you?

The R-Sq value shows that 23.5% of the change in case head expansion is attributable to pressure, and the remaining 76.5% is attributable to random error. If you like a measurement system that is 3/4 random error, then CHE is for you.

No matter what you do, case head expansion is NOT a reliable pressure indicator. If it were, that's what industry would use.

You will not look better with a rifle bolt where your nose once was.

Last edited by denton; 04/27/17.
Be not weary in well doing.