Not to detract in any way from Chuck's excellent post.

Oehler's description of their system
http://www.oehler-research.com/wizard.html

Modern gauge.


By 1933 Dupont was using piezo gauges attached to oscilloscopes. They used cameras to photograph the pressure curves displayed. The photo's were printed, then the data was transposed by hand to run the formulas so they could determine the pressure.

Crusher units in use from 1895 or so. This is currently on exhibit in the Curtis museum in Liege.


After each firing the lead had to be removed and measured.

Pete

http://www.damascus-barrels.com/Movie.html