Previous threads
https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=581069https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=255484&page=1 There has never been a U.S. government proof house
https://www.shotgunworld.com/threads/proof-testing-in-the-u-s.561455/ There have been, and are, independent testing laboratories.
Forest & Stream, November 24, 1894
“Gas Pressure or Bursting Strain”
https://books.google.com/books?id=19kwAQAAMAAJ&pg=PA459&lpg The proof-house charge of the American Testing Institution for a 12-bore gun develops a gas pressure of over 18,000 lbs. to the square inch. It is the same strain to which finished guns are put abroad. No gun would stand such a strain for any length of time. About 10,000 lbs. may be considered of touching the safety limit, and for some guns even is hazardous. A load giving about 8,000 lbs. pressure and less is better suited for the average gun and everyday use.
(This may be where the 8,000 psi [by crushers] recommendation came from)
April 20, 1895
Sporting Life “Shall Guns Be Tested?”
https://digital.la84.org/digital/collection/p17103coll17/id/48142July 27, 1895
Sporting Life Call for Government Proof House for Nitro Powder Testing
https://digital.la84.org/digital/collection/p17103coll17/id/48122 It was the position of the gun and ammo makers that testing should be done in-house, as today in the U.S. (and Turkey)
https://www.trapshooters.com/threads/proof-testing-in-the-u-s-and-turkey.939179/#post-9176306 I've looked and there are NO published minimal wall thickness
requirements.
Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives (C.I.P) has published recommended MWT numbers for the standard CIP proof pressure of 850 kg per sq. cm. (BAR) = 13,920 psi, for a service pressure of 10,730 psi
NOTE: CIP 12g “High performance/Superior Proof” Maximum Average (Service) Pressure is 1050 BAR = 15,229 psi
Maximum Statistical Individual Pressure 1200 BAR =
17,405 psi
Magnum proof 1320 BAR = 19,145 psi
(Magnum proof was originally 1370 BAR but was changed in 2006)
CIP standards do carry the force of law for member countries, unlike SAAMI standards which are recommendation (which of course the personal injury lawyers use)
Shotgun recommended minimum wall thickness for Category 1 “Standard Steel” (Non-alloy AISI 1045) with tensile strength = 101,526-123,137 psi
NOTE: the tensile strength of the standard steel used on U.S. doubles (primarily sourced from Belgium) through the 20s was 85,000 - 90,000 psi
10 & 12g.........................20g
End of chamber - .079”.......075”
4” from breech - .075”........071”
8” - .043”......................041”
12” - .030”.......................028”
16” - .024”......................022”
20” - .022”......................020”
Category 1 would fit the industry standards for 4140 Chrome Moly & 4340 Chrome Moly Nickel - both are “low alloy” steel
Category 2 (Non-alloy AISI 1060) and 3 (Alloy with 3% Chromium and 2% Molybdenum) with a Tensile Strength of 116,030 - 159,396 psi
10 & 12g end of chamber - .063”; 4” from breech - .06”; 8” - .035”; 12” - .024”; 16” - .020”
20g end of chamber - .059”
Category 4 steel has a Tensile Strength > 159,541 psi
We do now have a good collection of actual wall thickness measurements of presumed to be unmodified vintage doubles, which IMHO give us a very good idea of the numbers used by vintage doublegun makers.
