Raimey,
Here is the only picture I have handy right now. It shows the type style of the nitro proof visible on the barrels.
The letter "M" on each of the shotgun barrels (not shown) is clearly a letter M but it is rather an outlined tracing of a letter M.
The barrels were claimed to be full and full but I haven't had them measured personally to verify. I had heard that if another number is next to the circled-gauge proof it may mean the barrel has some amount less choke than full. The other 16 drilling had a circle-16 with the number 16 on one barrel (full) and the other barrel was circle-16 with the number 17 on the barrel and it was less than full. I'm not sure this is correct, but a drilling collector told me that was what it meant.
There is definitely NOT a cursive W encircling a K. There is a cursive W.K. on the barrel in just the same area you usually see the barrel mechanic's mark in the examples I've reviewed.
How can I learn more about Wilhelm Kelber or the A. Strover, Nordhausen individual mentioned on the gun barrels? I'd love to make a maker's label for the gun case that included his name and shop's address if I could find such historical information about the man. You seem to know so much about these mechanics and gunsmiths and I'm wondering if you are referencing a book?
Why would you guess 8x57r/360 before you would guess that a gun marked 7.8mmx57 would mean 8x57jr? Isn't 16/16/8x57 the classic drilling type most common?
I'll know more when I make a chamber cast later this week but I'll be very disappointed if this gun is a 8x57/360. I have zero interest in handloading and just sold ALL my reloading equipment a week ago. I'm an off-the-shelf guy now and 360 ammo is not of interest to me.
Thanks as always.
