And to confuse thing further
1933 lawsuit against Remington Arms related to the burst barrel of a Baltimore Arms Co. shotgun after using a Nitro Club marked Proof Load.
https://books.google.com/books?id=7p...C&pg=PA120&lpg
https://books.google.com/books?id=7p...C&pg=PA127&lpg
The “maximum commercial load” was described at “11,200 psi and 5 long tons” = 15,680 psi by Burrard’s conversion.
The proof load was “7 1/2 long tons or 17,800 psi”; 7.5 tons is 24,080 psi by Burrard’s conversion.
The simple formula conversion for 7.5 long tons is 16,800 pounds, which we understand doesn't work for LUP to PSI, but I wonder if the 7 1/2 to psi was miscalculated?
A Parker Service and Proof Load table was published in the 1930s and reproduced in the
The Parker Story p. 515. 12g 2 3/4” shell Service Pressure is 10,500 psi. Definitive proof used 7.53 Drams Black Powder and 2 oz. shot with a pressure of 15,900 psi. The pressure was no doubt measured using LUP and modern transducer values would be
10-14% higher, or more than 17,500 psi.
LTC Calvin Goddard reported the same numbers in “Army Ordnance”, 1934. He wrote that Parker followed the SAAMI standards of that period: 13,700 psi proof, 9500 psi service for 2 5/8” chamber; 15,900 psi proof, 10,500 psi service for 2 3/4” chamber (by LUP)
+ 10-14% for modern transducer measurement.