The rule of thumb for us in Europe is that guns are proofed at service pressure plus 30 per cent. Therefore service pressure is proof pressure minus 25 per cent. And bear in mind the British and Russian practice of stamping service pressure on their guns, not proof pressure as the rest do. So on a British gun the stamp 3 1/4 tons, or in a Russian gun the 750mpa are the service pressures, not the proof pressures. On all others the pressue indicated on the gun is the proof pressure and must be reduced by 25 per cent to figure the service pressure.
Proof pressure is the actual pressure the gun withstood during testing. Service pressure is the pressure it is meant to withstand in regular use.
Keeping it simple tends to keep it safe too.
