This gun, the subject of the earliest patent I was able to locate, uses a trigger mechanism somewhat similar to that seen in a real firearm. It has a trigger/sear element which engages a hammer. Pulling the trigger releases the hammer, which in turn releases the rubber band.
A semi-automatic design apparently similar in function to a "star-wheel/escapement" mechanism, but with a multi-part trigger assembly instead of a one-piece escapement trigger.
A star-wheel/escapement mechanism with an integrated cocking lever to assist with the loading process.
A "longitudinal string/strap-release" system with a sliding fore-grip as trigger, perhaps one of the first mechanisms to provide pseudo-full-auto fire.
Similar to contemporary pseudo-full-auto "sliding-ramp-release" mechanisms, but with release affected by a free-turning disk affixed to the slide. Per the inventor, the idea with the disk is to minimize friction as the rubber bands are released.
A longitudinal string/strap-release system in a pistol format, with a semi-automatic, strap-advancing trigger mechanism.
A pseudo-full-auto design wherein movement of the gun's fore-grip affects sequential release of rubber bands from a longitudinal array of pivoting retention arms. (I have a soft spot in my heart for this mechanism because it's similar to one I came up with independently as a youngster in the 1980s!)
A patent for a version of the semi-automatic "step-up" type of mechanism, currently popular among many rubber band gun enthusiasts.
A unique rapid-fire design originating in Australia and patented in the US. "It takes a bit of practice to use the Firewheel properly, but it's worth the effort given the capabilities it has," explains the Aussie narrator of the instructional video for the gun.
Perhaps the first instance of a patent for a pseudo-full-auto "rotary-string-release" type of mechanism. This fundamentally simple mechanism concept allows for a high ammunition capacity and is easily adapted to be to be motor-driven!
Another variation on the star-wheel/escapement mechanism. This version is found nowadays in popular, commercially-produced rubber band guns.
Some weird contraption from a guy in Alaska--probably doesn't even work (ha-ha)... Actually, this is my own patented design. It's a true full-auto, rapid-firing mechanism driven by a portion of the released elastic potential energy of the discharged rubber bands.
This design uses a pump-action version of the "step-up" mechanism as its basis. It's capable of multiple firing modes, including single-shot, rapid pump-action (trigger is held back as fore-grip is slid back and forth), and a shotgun mode, in which the gun's full load of ten rubber bands is discharged all at once.