This information was part of a separate thread, but will add it here
http://parkerguns.org/forums/showthread.php?t=10889
Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives (C.I.P)
http://www.cip-bobp.org/
Shotgun recommended minimum wall thickness p.4
http://www.cip-bobp.org/sites/defaul...e/A-4-1_EN.pdf
For
10 & 12g Standard Steel................................
20g Standard Steel
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”
FAQ
http://parkerguns.org/pages/faq/BarrelThickness.htm