I'll start with the Spray Can Cartrige, which I've mentioned in another thread.

The idea is to put a sprinkler valve in a spray can and use the can's valve to actuate it. This was initially intended for a semi/auto cannon that uses these cans as pressurized air cartridges, much like the Brocock air cartridges.
The second idea, the Rotating Loading System, comes from combining GalFisk's ball valve idea with H&K's feeding system on the G11 rifle.

I'ts a ball valve, with lever replaced and a hole drilled perpendicular to normal flow, plus a magazine epoxied on top of it (or below, but a magazine spring is needed), feeding projectiles vertically, just like in the G11 rifle.
The mechanism needs to be externally powered (from an electric or hydraulic motor). Coupled with a good compressor, it can make a very good auto. It can also be driven by hand, making it semi-auto.
1- Projectile (bullet-shaped)
2- Epoxy or similar adhesive
3- Reducer (from ball valve ID to barrel OD)
4- Modified ball valve