All Parker barrels were overload proved, regardless of year. See TPS p. 515 for the service load and proof load tables . J. G. is James Geary, the Parker barrel assembly superintendent, also as explained in TPS. In the mid 1920's , around 1925, Parker began using the Overload Proved stamp, although those barrels are no different structurally or dimensionally than previous barrels. Both fluid steel and damascus barrels were overload proved. Proof loads differed by guage and were the industry norm of the day, including 15,000 psi for 12ga when SAAMI standards were established in the mid 1920's. Again, for details, see p. 515, TPS. I have on occasion posted photos of the service and proof load table on this forum. For example, for a 12ga, maximum service loads of around 10,000psi are given. A Parker owner need not look very far to find loads at or below service loads.
Proof load psi should not be confused with rupture pressures.
Most questions regarding the Parker gun can be answered by reference to The Parker Story.
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