In the appendix to Burrard's "The Modern Shotgun" he reported on tests run in england in which a pressure gun was set up with a lead crusher on one side & a piezo electric tranducer on the other, thus recording both pressures simultaneously. An attempt was then made to work out a conversion value for the presures. It was found that for pressures within the normal range of shotguns this could be accomplished by the following formula. LP = crusher pressure & EP = piezo electric pressure;
(LP x 1.5) - .5 = EP. As the british use the "Long Ton" of 2240 lbs the tons can thus be converted to psi. This formula gives 8,960psi for a 3-ton "Crusher" pressure & 12,320 for a 4-ton crusher pressure. Where most confusion comes in is in correlating "Service Pressure" with "Proof Pressure". 12,320psi would be a proof pressure for a gun intended for a 3-ton (8960psi) service load while the 16,437 psi would be proof pressure for a gun intended for a 4-ton (12,320psi) service load. One of the Greener-Martini Police Guns I once had carried a 4-ton service proof. It would not have been intended to fire service loads of 16,437psi.
