A simple potato-pellet firing air rifle made from stuff that you can usually find in the shed...
This gun fires pellets cut from potatos, and is more or less accurate at 30 metres. It has a pressure chamber made a domestic waste piping bottle trap, and is filled using a valve from a bicycle inner tube. It has a trigger made from a washing machine stop valve, and a barrel from 15mm copper piping. It's put together with standard plumbing connections, and bolstered with a liberal amount of hot glue, and tape.
This video gives an overview of the finished potato rifle and shows it firing.
The rest of the Instructable takes you through the steps to make it - enjoy!