Here is the procedure for testing ammunition http://www.hpwhite.com/101-00.pdf

Based on ANSI/SAAMI Z299.2-1992 which basically says for 12ga,

Maximum average pressure: 11,500 psi
Maximum probable lot mean: 12,100 psi (a calculated figure)
Maximum probable sample mean: 13,000 psi (a calculated figure)
Proof loads (AKA Blue Pills) are 19,000 to 20,500 PSI

A selected number of shells from each production run are tested to provide a satistically meaningful result. To not do this is inviting litigation. There are many examples of ammunition makers issuing a recall.

The procedure for testing firearms is here http://www.hpwhite.com/100-00.pdf

If you want the complete ANSI/SAAMI specification it is for sale here: http://www.saami.org/Publications.cfm

Pete

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