A length of PVC for the barrel, 2-4 feet long, 2 inches in diameter
A length of PVC for the chamber, 8-12 in long, 3 inches in diameter
A male threaded adapter, 2 inch dia
A female threaded adapter, 2 in dia
A 3-2 in reducer
A female threaded adaper, 3 in dia
A threaded cleanout plug, 3 in dia
A gas grill ignitor
Construction:
1. Glue the barrel section to the male threaded adapter.
2. Glue the reducer to one side of the chamber piece and the female threaded adapter (3in) to the other.
3. Glue the female threaded adapter (2in) to the other end of the reducer. This will accept the barrel.
4. Make the ignitor by drilling a hole in the bottom of the cleanout plug and sticking the ignitor through it.
5. After letting this dry you just screw the barrel to the chamber and then load and fire.
The great thing about this design is that you can mix chambers and barrels, plus you can conceal it if need by taking the two pieces apart, greatly reducing the size. I have many chambers, and many barrels including my 6ft. sniping barrel and my suppresed one.