Prior to 1924, the Belgian and British Service (using) maximum load for 12g 2 1/2 and 2 5/8 shells was 1 1/4 oz. / 3 1/4 Dram Eq. (1220 fps). The pressure of that load would have been about 8500 psi with BULK smokeless powder; with DENSE smokeless 9,500 - 10,500 psi.
The standard 2 1/2 shells were usually loaded with 1 1/8 oz. shot and 3 Dr. Eq. of BULK Smokeless with a pressure of 6500 - 7500 psi; DENSE Smokeless was 9000 - 10,000 psi.

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