Rob,
The markings on the barrel (at least before the 1939 proof law) do not designate the nominal cartridge the rifle is intended to use. They show the bore (not groove or bullet) diameter, as measured with gauge pins in 0.1mm steps, and case length. To confuse matters more, the nominal cartridge designation is sometimes added in addition to the actual proof marks. This is why I asked for clear photos of the markings, since without them I can only guess. My guess it is the 8mm cartridge in the model M88 commission cartridge case with a rim added .
Mike
