unless you make the large tank at very high PSI, then this won't work (and i wouldn't recommend doing that for safety reasons). the reason for it not working is because, at low PSI, there isn't enough volume of air in the secondary chamber to fire any quantity of paint besides a single shot.
i've actually built a nice paintball cannon before, and i've drawn numerous designs. what you might want to do instead, is removed the secondary chamber and secondary valve, then make the main tank a smaller radius, but also interchangeable. that way, you could carry about 5 other full gas tanks, with 1 in the cannon. another plus about these smaller gas tanks is that they can be replenished by a simple bicycle pump right on the field in just about 30 seconds.
this is about half theory and half based on experiments. i think, if you use the interchangeable tank idea, you could shoot 5 paintballs (or the weight equivalent of in the shape of a larger round). this is, of course, assuming that your design is efficient. so, make sure the barrel isn't too long, there are no leaks, ect.
hope this helped
Homemade Paintball Cannon
