This is an instructable i made with 'Jewson'. It involves a wooden body and pvc pipe chamber and barrel.
WARNING: YOU MUST USE PRESSURE PVC PIPE.. OR YOU WILL HAVE NO FACE!!!!!
DISCLAIMER: I TAKE NO RESPONSIBILITY OF INJURY SUFFERED FROM USEING/ MAKING THIS PRODUCT
It took about 2 hours to make and cost about $10
Materials:
25mm pvc pressure pipe 50cm long with buldge on end
32mm pvc pressure pipe 35cm long
Block of wood 70cm x 27cm and 4.5cm thick
Ignitor (Lighter Igniter or preferably BBQ igniter)
Handle from hammer drill
2x Conductive Screws
1x Random Screw
Tape
Milk Bottle

Step 1: Barrel and Chamber

get your 25mm pipe and glue the bulge into the 32mm pipe with pvc cement. dont shoot the gun untill the glue has set. Follow the instructions on the glue. shave down the end of the barrel so it can cut through potatoes easyly.

Step 2: Body

Take your piece of wood and make a stencil similar to mine that will fit you chamber. Then Cut of the stencil. Do not include a handle we'll do that later.

Step 3: Trigger/handle

drill a hole in the body where you want the handle and screw it into place. the handle from the hammer drill has a bolt already in it.
drill a hole in the hammer drill to fit the igniter, then glue igniter in place. drill 2 hole in the chamber and then drill in screws, the screws should be about 1 cm apart so the spark can jump.

Step 4: Attaching Chamber/barrel to Body and Sealing Chamber

The next step is to tape the milk carton lid to the end of the chamber. Then you need to tape the chamber onto the end of the body. You could also glue it if you want.

Step 5: Sights/ Padding and Silencer

if you want a sight drill 2 holes side by side at the back of the gun and one at the front, then get small metal rods and hammer them in place.
for padding get foam and tape it on the back.
for a silencer see jewson's instructable.

Step 6: Finishing and Painting

Once you have finished tape the the chamber to the body once again to make sure its secured tightly. You can then paint it using primer on the pvc and black spray paint