Recently, I can upon an Imugr album by one “GarethWasHere”, which titled “Silling Mechanical GIFs” is anything but silly. The album is replete with innovative designs for semi-auto weapons (a side-locker, rotary en-bloc clip) and a few re-hashes of proven designs including lever-delayed blowback, gatlings, and long recoil.
The GIFs show an amazing talent for design, as each was likely rendered in a CAD program that required its own skill set to even create the recoil system designs, much less program the software for springs, motion capture, and turn into the GIFs that are displayed.
My particular favourite is the Gardner design, which features a mechanical design feeding two barrels from a single magazine. The Gardner is not a well-known design, but its simplicity in using cams to operate the entire firing sequence is fantastic.