Note that the markings for the bore on the German guns were put on by the proof house, not the maker. The gun in question would have been listed by the maker as a 9.3mm & not by the size stamped by the proof house. I do not have that many German guns, but the ones I do have also have the length of chamber stamped in by the proof house. The 72 is of course the length of the case & not the overall length.
US guns are normally marked by the cartridge's name, given by the whim of the originator. Thus we find .30-30, .30-06 & .308 Winchester all using the same diameter bullet & likewise with a .250 Savage & .257 Roberts. Then of course there is the .44-40 & .38-40, neither of which the name directly relates to bullet size.
