Chipmaker
( Can I assume you are a machinist?)The photobucket photos are too small to be of much use to me and I'm not smart enough to "blow them up". The 78/41 is the caliber of the drilling expressed in ga. This equates to 9.91mm and is the bore diameter,not groove or bullet diameter.As you mentioned, a chamber cast is necessary to determine the nominal caliber. The 16 in a circle is the chambering of the shotgun barrels and the 16/1 is the barrel diameter ahead ov the chamber.The rifle caliber marked this way means the drilling was made between 1893 and 1912,when the 1911 changes to the proof law came into effect. This age drilling wouldn't have a crown over V proof, it would however have a crown over U, which is the mark for "view" proof( a detailed inspection).I expect someone else will come along and address the steel type and Herr Metzner.
Mike
