I can't speak to the English proof rules, but SAAMI pressure standards for 2 3/4" and 3" shells are the same in 12 and 20 gauge, and for 2 7/8" and 3 1/2" 10 gauges. Because of this, it would seem to me that the same proof loads would be used for the longer chambered guns as the shorter one. Am I mistaken in this?














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