A coworker, Ron Harding built this wonderful contraption called a potato cannon. A basic potato cannon consists of various pieces of ABS piping bonded together, with A chamber on the back to hold the combustible gasses, and a long and narrow pipe as the barrel through which the projectile, usually a potato, is accelerated at high speed.
Some of us at work collaborated in demolishing some pre production versions of a soon to be obsoleted product that shall remain unnamed here. (This is to keep people who are looking for info on the product from finding this web page)
Having pieces of electronic equipment that have caused us much grief to aim a cannon at adds a whole new level of fun to playing with a black and noisy contraption that goes kaboom!
 
 
Note that the cannon at the time the shot was taken has already moved back by about 30 cm on account of the recoil. From where we found it, I suspect the object in the sky at the top center is the actual projectile.
This shot was not actually done with a potato. A rectangular hardwood 'plug' was used, with shop towels balled up behind it to provide a good seal. The blue haze at the impact point is most likely the shop towel.
 
The hardwood plug also had the great advantage of being reusable, as we had quickly exhausted our limited supply of potatoes.