Brent: scroll down just past 1/2 way here for an explanation of measuring pressure using crushers and a Tarage table
https://docs.google.com/document/d/1F2sQuPm05IE4VWYYnCkvuXmYEzQoWd_SQgaAfUOZEFU/edit?tab=t.0

Tons/BAR/PSI was measured using a crusher devices; converting a physical change in dimensions to a pressure number using a Tarage table. Lead for shotshell pressures; copper for higher rifle pressures.
Tons/BAR/PSI are now measured by piezoelectric transducers and there is no simple mathematical conversion from crushers to piezo transducers; adding 10 - 14% is pretty close for those of us not good at higher mathematics wink

BTW Great Britain adopted the 1969 Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives standards March 1, 1980 but continued using Lead Crushers to measure pressure (BAR) until 1989.

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