Last night I got an idea...
The reason paintballs jam is because you're putting an X amount of paintballs into a volume smaller than they're current volume, thus increasing the pressure, and friction, until the friction overcomes the force that's moving the paintballs...
So the jams would occure in the area where the volume is being decreased, so if you put that area in the mass of paintballs where jam's cant occure instead of at the nozzle, then it shouldn't jam.
Simply put, I'm preatty sure something very simple could actually solve this, a small slant on the top of the clip;
Yellow: Jam Zone
Orange, is a small hole I'd drill, so a screw could fit in it. That way I could jam the floor down with mabye a small rod, and put a screw in to hold the floor down while I fill it with paintballs.
Now what do I do about the offset, I could cut out some metal so that the clip goes all the way up to the chamber, but it needs to be forward a lot more...