Please see
http://www.16ga.com/forum/viewtopic.php?t=3428 and thanks to Larry Brown
Per the 1954 Rules of Proof, here are the equivalent service pressure values:
3 tons--8,938 psi
3 1/4 tons--9,682 psi
3 1/2 tons--10,427 psi
4 tons--11,917 psi
These numbers SHOULD apply to guns proved under the 1925 rules, which were stamped only with chamber length and shot charge. Thus, a 2 1/2" chambered gun, 1925 rules of proof, would be equivalent to 3 tons; a 2 3/4" chambered gun to 3 1/4 tons.
A service (using) pressure of 3 tons per sq. in. = 8,938 psi service pressure (SAAMI) BUT please keep in mind that pressure does not equal recoil (which is a function of shot charge and velocity.) Pressure stresses the action, recoil the wood (and the shooter.)
