The 6.5x55mm cartridge is from 1891 and registered at 55,110 psi in Europe and 51,000 psi in the US.
The case head is good for ~ 67 kpsi and long brass life.
If one works up to extractor groove growth threshold [indicator for primer pocket growth] and backs off 6% powder charge aka Vernon Speer 1956 on how to write a load book, the pressure will be ~ 65kpsi, like the registration of a 22-250, 6mmRem, or 270Win that use the same Mauser case head.
