This from the guys over at the Firearms Blog, who are better at ferreting this stuff out than I am when I get busy:
The blackpowder cannon enthusiasts over at the Graybeard forums came up with some amazing pieces of artillery.Damn that new weapons technology! First it was little bitty revolvers...now it's little bitty cannons. What's next...little bitty cruise missiles? When drill presses are outlawed, only outlaws will have drill presses...
CU_Cannon built the “Nano-mortar”. It fires .177″ BBs. The bed it sits on is 1″ long.
The pico mortar was build solely with a drill-press, some files and emery paper. It fires 3mm shot pellets (0.118 inch diameter) and has a maximum load of 0.2 grains of blackpowder. It has a barrel length of 8mm (0.315″) and can fire 6 meters (20 feet).