Joe is correct. The illustration in no way represents wall thickness recommendations
https://docs.google.com/a/damascusknowle...TEK8OtPYVA/edit

Commission Internationale Permanente pour l'Epreuve des Armes ΰ Feu Portatives (C.I.P) http://www.cip-bobp.org/
Standard CIP proof pressure of 850 kg per sq. cm. (BAR) = 13,920 psi proof pressure = 10,730 psi service pressure (SAAMI)
Shotgun recommended minimum wall thickness (p.4) for Standard Steel with tensile strength 700 - 849 N/sq. mm = 101,526-123,137 psi
http://www.cip-bobp.org/sites/default/files/new_file/A-4-1_EN.pdf
PLEASE NOTE: actual tensile strength testing on a sample of pattern welded tubes averaged about 54,000 psi

For 12g Standard Steel.................................................20g
End of chamber - .079”..................................................075”
Just past the forcing cone/ 4” from breech - .075”................071”
8” - .043”..................................................................041”
12” - .030”.................................................................028”
16” - .024”.................................................................022”
20” - .022”.................................................................020”


More information, and opinions, which are all any of us can offer
https://docs.google.com/a/damascusknowle...nvwLYc-kGA/edit

Previous discussion here
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=379803#Post379803

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