There are quite a pile of Maxim patents in the US Patent Office and there should have been a LOT more.
Fact is, Maxim's brain was looted at every opportunity and by every hustler and promoter who got close enough to find something they could steal.
Maxim lit NEW YORK with electric lights while all the ballyhoo and publicity was about what the glorious Edison was GOING to do. Maxim was making the first electric light bulb with a coiled, drawn platinum filament in an inert-gas atmosphere while Edison was using Maxim's old filament carboniser and vacuum pump to make the "First Electric Light" and get the patents filed before Maxim could file his application for a FAR superior light. Fact is, Edison patented one of Maxim's EXPERIMENTAL types while Maxim was designing the FINISHED PRODUCT: the electric lights we use today.
By the time Maxim got into making guns, he had learned a simple lesson: patent EVERYTHING.
There is NO automatic firearm which has ever been built, anywhere, which does NOT violate one or more BASIC MAXIM PATENTS. He worked on every type which it is possible to build: straight blowback, retarded blowback, short-recoil, long-recoil, gas-operated, even primer-actuated. He patented toggle locks, sliding breech-locks, wedge locks, magazine feeds, open feeds, belt feeds, pretty much you-name-it. If it could be used to make an automatic gun mechanism, it is highly likely that Maxim worked with it, built it and patented it. This includes boosters, rate-of-fire regulators, feeds, bolts, buffers, cooling, even the SHAPE of the crank handle (which countered the recoil thrust of the gun, assured a strong loading cycle and simultaneously prevented battering). When they were capitalising Vickers, Sons and Maxim Ltd., Maxim contributed patents valued at $4,500,000 at that time: nearly $150,000,000 in today's debased 'money'.
Maxim's very FIRST automatic Machine Gun was built in 1883. It worked rather well and fired more than 150,000 rounds in public and private demonstrations. It is in the Imperial War Museum in the reserve collection. I identified it for them positively in 1976 when I was in England (the GUN was in the IWM, the documentation still was in the Science Museum, being kept on file when the Gun was disposed-of) and I have had my own two hands into its sacred guts. It uses the T-slot extractor which "everybody KNOWS" was invented by that great 'Merican designer John Moses Browning..... in 1895: TWELVE YEARS LATER. Browning also stole Maxim's (patented) belt feed, water cooling, booster, flash hider, short-recoil system and a few other little things.
By the way, the Improved Maxim Machine Gun also introduced an interesting little idea into manufacture: MODULAR CONSTRUCTION. Anything goes wrong with a Maxim Gun in the field, the Gun can be rebuilt in NINETY SECONDS OR LESS.
Maxim also built an airplane the size of a World War Two heavy bomber and proved that it could fly and could be controlled, in 1896: seven years before the plucky AMERICAN Wright brothers (who had read up on Maxim's experiments) got theirs off the ground.
The Nineteenth Century produced TWO absolute GIANTS in Engineering. They were Isambard Kingdom Brunel and Hiram Stevens Maxim.
It is indeed a tragedy that neither is known or honoured today.
BTW, yes, I DO drink Maxim coffee. He invented the stuff, didn't he? Likely the manufacturers don't even know!