"the Ithaca Model 37 and Winchester Model 12 and they appear to have very thin barrels, although I've never measured one. These types of lightweight repeaters have been made by the millions, all without the "benefit" of proof"
Ithaca advertisements stated that barrels were proved with a "double charge of powder and 1 1/2 times the normal shot load"; or (possibly) 6 1/2 Drams Black Powder with 2 1/4 oz. of shot if the standard load was 1 1/8 oz. shot and 3 1/4 Dram Eq.
Jack O’Connor wrote in
Outdoor Life in 1942 that Lew Smith, President of Ithaca Gun Co. stated the Proof Loads were 17,500 psi.
The receiver end of Ithaca 37 Featherweight barrels is marked "Proof Tested"; not sure when that started
The Winchester 1897 listing in 1904 H.H. Kiffe catalog
"The barrel of this gun has been proved with 9 1/2 drams of powder, and 2 1/2 ounces of shot."
The
Banc D'Epreuves Des Armes a Feu De Liege (Proof House for Firearms of Liege) First Obligatory Proof Load for 12g breech plugged tubes intended for "Double-Barreled Breech-Loading Sporting Guns" was 21 grams = 324 grains = 11.8 Drams powder and 32 grams = 1.12 oz. shot.
For comparison, British Provisional Proof (tube bored, ground, and with chamber cut and threaded for a plug) 1855-1925 for 2 1/2” and 2 5/8” 12 gauge shells for a service load of 3 1/4 Dram Eq. with 1 1/4 oz. shot was 9 3/4 dram “Tower Proof” (“R.F.G. 2”) No. 4 or 5 Black Powder with 1 1/4 oz. shot.
It has been well established that the vast majority of "rough forged tubes" used by U.S. shotgun manufacturers prior to WW1, and even until WW2 were sourced in Belgium; both damascus and (with the exception of Winchester and Remington) Decarbonized and fluid steel, and therefor received First Obligatory Proof at the
Banc D'Epreuves Des Armes a Feu De Liege.
See:
https://docs.google.com/document/pub?id=17ixogftgITEblNUWtmFBv96ZvgjK6eFell8GsAWd-KI More on U.S. makers proof here
https://docs.google.com/document/d/1F2sQuPm05IE4VWYYnCkvuXmYEzQoWd_SQgaAfUOZEFU/preview