Hermano Campero: a helpful chart from “Proof Tests and Proof Marks: Practices of Manufacturers in the United States”, 1934. Limits are based on the 1925 British Rules of Proof. Long tons are converted to PSI simply by X 2240, and the numbers were measured by LUP so require adding 10 - 14% for modern piezo transducer numbers.
It is important to note that the standard 28g load then was 5/8 oz. and 2 1/2" .410 only 3/8 oz. The 2" .410 was 3/10 oz.

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Modern U.S. SAMMI standards for 28g and 2 1/2" .410 allow max. pressure of 12,500 psi; 3" .410 13,500 psi.
12g and 16g are 11,500 psi and 20g 12,000 psi

The current CIP standards allow for greater pressure https://www.scribd.com/document/97965210/CIP-Shotshell-Pressures
28g is the same as 24g

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but slightly LESS end-of-chamber wall thickness for small gauges, but the Category 1 “Standard Steel” is Non-alloy AISI 1045 with tensile strength = 101,526-123,137 psi
Category 2 is Non-alloy AISI 1060 and 3 Alloy with 3% Chromium and 2% Molybdenum with a Tensile Strength of 116,030 - 159,396 psi