Thanks for the great pics and links, Professor.
I think I figured out how it works.... the side button lever raises/lowers a wedge that fits into positioning cuts/detents on the right side of the magazine tube. The bottom spring catch engages the cartridge follower rim and pulls it towards the muzzle, then becomes a detent for the cartridges as they are pushed past it. One cartridge goes into the carrier, maybe first, I dunno.
Upon moving the forearm rearwards the catch is cleared by riding up on the outside of the magazine tube, releasing the cartridges.
The follower is the key - it resembles a bullet with a single, wide grease groove. Got that from studying the English patent from Houze's book.
anyone got a 66 receiver and/or round barrel ?
T4t