G.T. Garwood's "Shooting Facts & Fancies", A&C Black Ltd., London, 1978, addresses the inertia issue of pump guns. He states that, " the ordinary pump gun has an innate tendency to work automatically. This arises from the fact that when the gun recoils, the fore-end and associated parts are compelled to recoil with it. But when the gun is brought to rest by the resistance of the shooter's shoulder, these same parts are free to continue their rearward course, and if only they had enough inertia, they would do so and would eject the spent case and recock the gun. What is more, if there were a light return spring, the fore-end would then return of its own accord to its original position, feeding a fresh cartridge into the chamber in the process, whereupon the gun would be ready to fire again.
But how much weight would it be necessary to add to the fore-end of a pump gun to make it work as a self-loader? My immediate answer to the doubt that has been raised is that the hand and forearm of the shooter, added to the weight of the fore-end, and reinforced by anticipatory pressure, are, in my opinion, quite capable of achieving the first part of the double-movement without conscious effort; and that the second part can equally unconsciously be achieved by the instinctive recovery from the recoil.
So, I do not think that there is anything remote about the prospect of working a pump gun subconsciously."
Garwood went on to state that this is the principal of the Benelli autoloader wherein "the recoil kicks an internal inertia weight and sends it flying back against the action of a light return spring to perform all the functions just described."