I don't know anything about these, but I did find an old catalog of some sort that included a picture of the component parts of this shotgun (pointing out it's construction). That spectacle piece at the front of the barrels is shown, along with a monobloc and barrel tubes. I am surmising that it was a novel assembly technique where the barrels were inserted into the monobloc and the spectacle in order to simplyfy assembly at a controlled spacing. Not a bad idea. Slide them together, clamp on a fixture and solder. Laying the ribs then becomes a lot simpler.
