Thanks guys!
It always helps to have the support of your friends to overcome difficult obstacles.
Right now im in the process of drawing up the plans for a regulated co2 powered 57mm recoilless rifle. Its going to be breach loading, and have the advantage of using seperate shells, rather than packing the bbs down the barrel like a potato gun. It will have its own bolt assembly that will be able to accept the shells, which will also have to be made in addition to the weapon. Each shell will be made out of 2in. steel tubing, and about 6in. long, with an aluminum rim at the back so it can be extracted by the bolt. There will be no need to gas up the shells, because the gas is stored in the gun, and upon firing, passes through the shell, and propells the bbs inside, down and out the barrel. Each shell (roughly the size of two soda cand stacked end on end) will be able to accept from 500 up to 1000 bbs each. And with a bunch of them, one after the other, thats alot of bbs. Howlers will also be albe to be loaded in the shells for a realistic "artilary" effect.