Actually I have seen some very successful airsoft AT-4 launchers built that way or similar. The Nerf football comes out with some good stank on it too. Firstly you have to have the Nerf footballs with the tail fins on them, they're actually quite small. Second the CO2 carts were pre-punctured into a reservoir in the back I believe, and then the device fired by valve or button release if memory serves. You won't be able to go full mortar style though as the football won't have enough weight to actuate a primer or release. You could drop it in and then manually release though. I think you only get one shot per cart as well. Buy the footballs online in bulk. They are relatively hard to find and some of them went so far we never found them again. As for exact schematics I can't say, built by members of JOC in Calgary. I've only fired it once myself and seen it fired numerous times.
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