Large Cannon Question

[iamthewalrus]

Ok, its almost potato season here again (Been to cold for my propane, to lazy to compensate) so i thought i would start off my season with a LARGE cannon. i have in my possestion about 3-4 feet of sch80 8" pipe. I plan on making half of the pipe the chamber for a propane injected combustion, and the other half of the pipe the barrel (yes only a 1.5ft barrel) to use to launch canntalopes or pumpkins or sum s*it. i was jsut wondering if anyone knew about how much distance i would get with this or if anyone has a better C:B ratio for me with my pipe. Muchas Gracias from Mr. Walrus