Raimey;
Again not disagreeing with any of this. My only point was (& is) that it is the lack of other markings & not the fact the nominal gauge is in a circle that would likely denote the gun in question to be chambered 65mm.
My gun is of ca 1901 vintage & was an export model. It has neither a date code or Nitro Proofs. I cannot say with certainity if the 70 was stamped in the extractor by Sauer, the proof house or by VL&D but unlike the example Larry cited mine is in metric rather than 2 3/4".

Miller/TN
I Didn't Say Everything I Said, Yogi Berra