I seem to remember a course at Linton on 72sqn built a monster of a cannon which was christened "The Chief." The barrel was a 6 foot length of steel pipe and the combusiton chamber was a fire extinguisher. Lynx deodorant was the propellant and it used coke cans for ammunition. The whole thing sounded like a mortar going off and won the inter-squadron mess cannon competiton hands down. As for the range.... No Idea, we never found any of the cans fired as it was a misty day and vis was down to 500m so no impacts were seen!!
Not really suited to indoor use though!