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!
Step 1: The Pressure Chamber
Step 2: Pressure Valve
To fill the chamber you need a valve.
This uses a normal bike valve. Cut it out from any old inner tube that has been lying about in the garden. It's pushed through a hole drilled in a standard end plug and then sealed with hot glue.
Bicycle technology is awesome. It pre-dates, and was used to develop planes - fantastic!
Step 3: The Trigger
The air chamber allows air to be be pumped in to create the firing pressure. To release this, you need a trigger to let the pressure out from the chamber quickly. This uses a stop-valve from a washing machine.
Step 4: Fitting the Barrel
The barrel is domestic 15mm plumbing, attached using whatever joints can be found in the shed/DIY shop. Use lots of PTFE tape to get the seal tight.
Step 5: Sharpening the Barrel
The inside of the barrel should be sharpened so that the outside of the barrel has a cutting edge. This makes sure that when inserted into a potato, it cuts a plug wider than the inside of the bore of the barrel. This makes it a tight fit, so that it does not let gas out and fires with the most energy.
Step 6: The Finished Gun
Put together, it looks like this...
Step 8: Priming the Gun With Air
Once the plug is cut (and making sure the trigger is closed!) prime the gun by cranking up the pressure using a pump. A decent barrel pump or car pump is best.