Thanks for explaining the weapon. It makes more sense now. One question though. Since this wasn't gas operated was it actually a true semi or a pump?
It's a true semi-automatic. Recoil operated, like almost all semiautomaic pistols. The very first semi-auto shotguns were recoil operated. In fact, IIRC, the first semi-auto shotgun was designed by the same gentleman who deisigned the "Colt" 1911 Hi Power pistols (also recoil operated), the "Colt" Potato digger" the M1917 and M1919 machine Guns and the M2 .50 cal machine gun. John Moses Browning.
Both Remington and Browning made "humpback" semi-automatice shotguns to the JM Browning design.