Prior to 1924, the 12g Maximum Service load was about 1 1/4 oz. / 3 1/4 Dram Eq. (1220 fps).
After the proof house revisions of 1924, a Certificat depreuve could be issued and specified:
The pressure developed, measured by crusher type device, lower or equal to 600 kg per square centimeter for sizes 16, l2, 10, 8 & 4; 670 kg per square inch for sizes 20, 24 and smaller.
600 kg/cm2 = 8534 psi maximum SERVICE pressure;
670 kg/cm2 = 9530 psi maximum SERVICE pressure
+ 10 - 14% by piezoelectric transducer measurement
(Very similar to modern load pressures)
12g PROVED at 900 kg/cm2 = 12,801 psi; or about 14,000 psi
BTW: the barrels are dcalcomanie Faux Damascus; fairly late for that embellishment.
The Crown over D indicates that the tubes were by Delcour-Dupont of Nessonvaux, which became Canons Delcour which was registered in 1921, and remained in business until about 1968 when they were acquired by Fabrique National de Herstal.
Canons Delcour also supplied fluid steel tubes for Hunter Arms, Fox, and Ithaca NID (Best Fluid Steel) and Ithaca Lefever Nitro Special A-grades.
