Thanks to all who have responded.
Mike. Could you explain how the 78/41 is converted to gauge and into mm. The 9.91mm (.3901") is consistent with my measurement of .3930". Also how does the /1 change the diameter of the 16 gauge ? Chamber cast tomorrow.
Raimey. I've attached photos of the marks that you circled. Yes the top tubes are rifled. I'll include some of the bore with the chamber cast. Do you know anything about Metzner? Did he retire/die in 1901 ?
m-4 . The mark that you asked for is the one on the bottom just above your post. It looks like an (*) to me.
Otto
