I used to own one of those that I bought from Letterkenny Army Depot for $17.50 many years ago. I sold it (at a small (?) profit) to a collector of military shotguns.
IIRC, there is no recoil operated slide lock on that gun. The slide unlocks when the hammer falls. Further, there is no disconnector; if the trigger is held back the hammer falls when the slide goes forward, so the gun will fire as fast as it can be pumped.
FWIW, patent drawings often don't look like the production item, since they are based on the inventor's model. The reason for a patent is to get some concept protected, not to produce engineering drawings. In addition, it was common practice at that time to put on as many patent dates as possible, even if the patented item was not used on that gun. I guess the idea was to impress the buyer and intimidate the competition.