Are there recommendations for barrel wall thickness?

1. The Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives (C.I.P) minimum wall thickness recommendations for ‘Standard Steel’,  defined as a tensile strength 101,500 - 123,000 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”


2. The average tensile strength of both Crolle Damascus and Twist is about 54,000, a bit less than Decarbonized or Siemens steel. There was however only a slight difference in the performance of pattern welded vs. late 1880s steel barrels in the  Birmingham Proof House Trial  
   http://docs.google.com/a/damascusknowledge.com/document/d/1dnRLZgcuHfx7uFOHvHCUGnGFiLiset-DTTEK8OtPYVA/edit?pli=1

   
   
3. Higher tensile strength fluid steel was developed rapidly after 1890.

   Krupp Nickel Steel patented in 1890: 92,500 psi

   Winchester Nickel Steel, introduced about 1896: 100,000 psi

   Remington Ordnance Steel, introduced in 1897: 110,000 psi

   ONE sample of Hunter Arms Co. Armor steel, introduced in 1898: 101,000 psi

   1905 Krupp Chrome Nickel Steel D: 106,500 psi

   Marlin “Special Smokeless Steel” introduced for the Model 1893 rifle in 1897 and Model 21 Grade C Pump in 1907: 100,000 psi
   

4. In 1918, Sears advertised the Fulton/Gladiator barrels as having a tensile strength of 85,000 – 95,000 psi.

   The ‘LLH’ mark of Laurent Lochet-Habran is frequently found on L.C. Smith Royal, Armor, London, Crown and even Nitro Steel barrels from 1914 to 1948, Hunter Arms Fulton, Gladiator and Ranger for Sears, and also Fox, Ithaca, Lefever, and Baker guns.

   This figure may therefore reflect the strength of the post-1900 Belgian ‘rough forged tubes’ used by most U.S. makers.
   

5. The industry standard for modern AISI 4140 Chrome Moly gun barrel steel is 95,000-100,000 psi.
   
   More information may be found here
   http://docs.google.com/a/damascusknowledge.com/document/d/1LFnSG34k3mBhLEjEgU267wAlIa215MNVQZhIiY62Hx4/edit?pli=1
   
   Recommendation:

   I would not shoot any barrel, pattern welded or fluid steel, that is deeply pitted and has a wall thickness less than .020" in the distal 1/3 of the barrel because one cannot know the wall thickness at the bottom of those pits.
   
   Minimum Wall Thickness recommendation for Damascus or Twist barrels:

   End of chamber - .105"
   Forcing cone - .100"
   9" from breech - .040"
   9" from muzzle - .025"

   Every vintage shotgun, and shotgun barrel, should be evaluated before use by someone with the equipment and expertise to properly do so, and then shot only using ammunition with ballistics similar to that for which the gun was originally intended.