Skeeter, the 740 bar pressure you mention as proof pressure is in fact the service pressure for 12 gauge guns of less than 76mm chamber, ie non magnums.
If the chamber is 76mm then the gun must be submitted for compulsory proof at 1370 bar. The same standard is vountary for 70mm chambered guns. The compulsory proof for standard chambers is 960 bar.
This leads to some confusion in Europe because there are 70mm shells generating 1050 magnum service pressures, but these are marked on each shell (thankfully!), not just the box. To add to the confusion Proof Houses do not have a clear numerical indication of pressure, most having a stamp which the public are expected to interpret.
Proof pressure have changed over the years, the latest changes came about in the early 1990s when magnum proof pressure increased from 1200 to 1370 bar and regular proof from 900 to 960 bar.
You can get the CIP table showing proof and service pressures for each gauge from the CIP site.
Crowley, what do these "proper" proof marks say?
Last edited by Shotgunlover; 04/05/14 06:34 PM.
