I was always curious about the proof markings on British rifles - often in "ton per square inch" - was not sure what that meant. I believe is a result of the British proofing process, like at Birmingham or London proof houses - was actually measuring the axial load - we would call that the "bolt load" or the "bolt thrust" - is not exactly the same as SAAMI concern about radial pressure, although I am sure the two have to be related somehow. British measuring systems also used "long ton" and "short ton" - I do not know which was used in their proofing testing - they are different to one another - so I have never figured out how to convert a British "ton per square inch" into "Pounds per square inch" (PSI) like we refer to more often. For sure, the "tons per square inch" were measured in a different place in the chamber, than what SAAMI specifies. And just to confuse even more, a lot of the USA military stuff reports in units of Copper Units of Pressure (CUP) which are a different again way of measuring and reporting pressure - all has to be related somehow, but I know that CUP in a 30-06 is not the same unit as CUP in a 7x57 ... A correspondent sent me a copy of a conversion worked out by a math guy to convert CUP to PSI, but is not a constant value - is not like converting pounds to kilograms, or converting miles to kilometers - has more "ciphering" involved to it.
I was never able to find out if the stamping on a British proof was saying the "approved" service pressure, or the actual "proofing pressure" that was used.
There is a table on Internet at
http://kwk.us/pressures.html that purports to show the PSI and equivalent CUP values for various cartridges - showing both the USA SAAMI standard, and the European CIP standard for the same cartridges. Some are the same, some are not - sometimes PSI is bigger number than CUP, sometimes other way around. But I think the pressure is actually the same - PSI versus CUP - just a different way and different place to measure it - if the data source is true.
CUP and PSI as used by SAAMI are two different pressure measuring systems. In some calibers, the pressure sensor is at a different place, so the limit quoted for that place is different in the two systems. In some calibers the pressure is measured at the same place and the pressure limit is the same number.
308 is one of the calibers where the pressure point is different, and the limit for the CUP system is about 50,000 psi, measured the CUP way (measuring the compression of a lead or copper slug) or about 62,000 psi measured with a electronic transducer.
When I first started working in a lab, all we used was lead and copper crushers, and we called the results "psi". When some calibers started to get measured with transducers, we changed the nomenclature to "CUP" and "psi", so there was no confusion.
Unfortunately, the old paperwork still exists, where the pressures are all quoted as "psi" but they did not mention that this was using the CUP system. They did not specify, because, at that time, CUP was the only way pressure was measured and everyone knew what we were talking about.
The old military documents specified a 7.62x51 max pressure of 50,000 psi (with no mention that this was measured by the CUP system). This has caused the myth that military ammo is lower pressure. Not so. The max pressure for 7.62.51 is about 50,000 CUP or about 62,000 psi. Same pressure limits, just measured with different systems at different places.
Most 308 or 7.62 ammo is around 55,000 psi, although I have seen both 308 and 7.62 (Winchester Supreme and IVI ball) at around 62,000, and I have found some commercial 308 as low as 50,000 psi. (Norma)
As for the Spanish carbine and the FR7, I use a reduced pressure load. Not because of any weakness in the rifles (we used to use the small ring Mauser for 308 target rifles and fired hundreds of thousands of rounds in them with no problem) but because the old design does not handle gas from a blown case or primer very well. It tends to blow crap back into your eye.