Looks just like an experiment a Trinidad State J.C. Gunsmithing student did in 1967. It was called the 7mm Shot Rifle. Long neck for multiple round ball stacked. A real shotgun made better groups with Buckshot! Not a new idea. If you see this, John, I am talking about you!
The reamers were made by a long ago reamer maker in Raton, NM named Mayer just for that project.