My understanding, from more than one major pressure lab, is that the 7mm RM shows a wider spread in pressures than most other cartridges of the same class, both high and low. Which is why the SAAMI Maximum Average Pressure (MAP) was set at around 60,000 PSI when piezo-electronic pressure-testing became standard.
Some other rounds have a SAAMI MAP of 65,000 PSI, which is as high as SAAMI will go, but they also have standard for what the highest-pressure round in a string measures, to allow a safety margin.
