Frank: the more we all think about this the better...and I still think the Brits enjoy(ed) messing with us
What I assume: The Tarage table used to convert compression of lead crushers (distance) to pressure reported either PSI OR
Long Tons.
What I know:
This pressure/distance curve appears on p. 20 of "Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics" by Wallace H Coxe, 1931
On p. 21 Coxe states "The vertical line represents the pressures developed by the various powders. This is measured in long tons (2240 pounds)."
Major Sir Gerald Burrard wrote in the Third edition of
The Modern Shotgun, 1955, Vol. 2 that pressures derived from simultaneous crusher and piezoelectric transducer pressure readings in a test barrel demonstrated the under-reporting of pressure by (crusher) LUP compared to piezo transducer gauges:
“The calibration of lead crushers by means of the piezoelectric gauge suggests that lead crusher pressures are somewhat on the low side; 2 Tons per square inch being about 2.5 with the piezoelectric gauge…”
And for that reason he came up with his formula to convert pressure as measured by lead crushers expressed in Long Tons to PSI as measured by modern piezoelectric transducers.
That ALSO means PSI as measured by crushers is less than that as measured by transducers, and “Eley Shooter's Diary 2005” states “The later transducer system uplifts the (PSI by LUP) values by approx. 14%.” Other authors say 10% - 14%.
What we
don't know:
When were pressures reported by U.S. gun and ammo makers measured by piezo transducers?
We DO know that the
Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives standards ratified in 1969 expressed the pressure numbers as transducer BAR converted to PSI.
BUT the darn Brits didn't adopt the
CIP standards until March 1, 1980.