OK friends, I picked up the Mnchner Bchsflinte this afternoon. I should slug the bore myself, as I have some 50 caliber round balls, but here are the measurements from the chamber cast:
Groove 0.471
Case mouth 0.513
Base 0.525
Rim 0.605
No shoulder whatsoever.

These dimensions are a little bigger than the 11.7 mm Danish. A new 45-70 case drops right in, but there is a good deal of radial clearance. The closest thing I can find is 12.3x50R Mauser Straight. Matches the rim for sure.

This gun opens by rotating the forearm clockwise. There is a wedge that holds the forearm in place. The shotgun barrel measures 16 ga. IC.

What do you think?

PS: New lead slug measures 0.470, no real change. Very wide grooves.

Last edited by ligonierbill; 10/08/18 06:55 PM. Reason: Addition