Here is my 2nd cannon and I decided not to go too crazy but chamber fan and metered propane soon to come. Oh, and a red laser mounted to a rail at the chamber end of the barrel, currently waiting on laser.
There is no paint on the gun it is all black and red electrical tape because I do not have the patience to wait for paint to dry

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It is powered by a 150kv stungun with 4 sparks.
Then your normal 4in chamber to 2in barrel. I dont know how true this is but to me shooting 2in spuds seems to be more fun then 1.5in.
The definition of spudcannon should include combustion, if I wanted to shoot a pneumatic I'd go get my paintball gun.