The old German proofmarks, as used from 1912 to 1939, often confuse moderns, especially Americans. Most German proofhouses marked not part of the cartridge name nor the larger groove or bullet diameter, but the smaller bore/land diameter. It was measured at the proofhouse using cylindrical plugs in .1 mm increments. Here a 10.8 mm plug passed the bore, but a 10.9 mm one did not. So the actual bore diameter may have been 10.89 mm. You have to add 2x the groove depth of about .1 to .2 mm to get an idea about the groove or bullet diameter.
So I think the 10.8 mm bore and 72mm case length point to the old 11.2x72 Schueler cartridge rather than the .404.