What is the letter type on the "Nitro" stamp for the scattergun tubes? Without handling it or a pic, I'd guess the 1/29 is the proofdate and Wilhelm Kelber was the mechanic who performed the tube assembly work. Is the "outlined letter M is present on each barrel" actually a cursive "W" encircling a "K"? 0.318" wasn't made obselete until the 1939 proof rules. I'd first guess 8x57R/360 and then go from there. There's not a full choke designation, just a "Crown" over "W" which notes that at a min. there is/was 0.008" of constriction at proof. Look forward to the pics.

Kind Regards,

Raimey
rse