Culit,
I didn't "blow up" any of the photos, until you mentioned a 70 on the extractor. Such a mark, indeed, indicates the chamber was lengthened to 70mm (2 3/4") and special ammunition is not likely required. My opinion differs from others very often, but polishing the barrel flats as you described would not hurt at all. If my German gunsmith friend took this gun in for any work, he would likely also polish the barrel flats, the sides of the locking lugs, the extractor, and the muzzle, if corrosion was present; I saw him do this many times, just as an automatic service. These are areas that would have left the factory polished bright. If these areas are blued on a German gun, I would suspect it was reblued in hot salts making the rib solder joints suspect. In my opinion this gun should be used and cherished by you and/or other members of your family.
Mike
My gunsmith, CJO from this board and many of you are familiar with the quality of his work, would polish those areas as well.
