I just got this trench gun on Thursday. The seller told me that it is a 1922 vintage gun. The gun has been reblued as expected and I think the stock is a replacement. Unless the interwar stocks did not have sling swivels.
The side of the receiver has been polished or reworked and it broke through to the screw hole under the ejection port.
What about the bayonet adapter? I think it may abe a replacement. It has seams on the top and bottom like it is cast.
The barrel is 20" and Cyl marked with a six-row heat shield.
I didn't pay much for the shotgun, more than a Chinese copy, but far less than a collector quality trench gun.