2g Sch.P means 2 gramm - 31 grain Schultze Pulver, the schultze nitro powder also use in america
27 31 is a ? normally is it one bullet weigth, 27 or 31gramm?
in any case this is not the proof load, it is the load the gun was build for.
the S&B and the the RWS load now back in production shut be safe in any gun you find with this chambering.