Parts (all parts are schedule 40 PVC)

1.)  3" by 3" by 1,5"(looks like a lower case y(see below))

2.)  3" to 4" bell reducer(looks like a funnel)

3.)  4" PVC that is 10.5" long

4.)  3" Cleanout and cap(it screw in)

5.)  1.5" Clean out and cap(it screws in)

6.)  About 3" of  3" (this connects the reducer to the chamber)

7.)  PVC cement(make sure it says that on the bottle)

8.)  PVC Primer

9.)  BBQ igniter or Pneumatic Add-On.

10.)  A couple pieces of cardboard to make a wadding)

11.)  Of course a couple rolls of toilet paper!!

Assembly

PVC Parts

Assemble all parts to look like the diagram below.  Cut the barrel to length.  Then take you PVC primer and spread it on all the joints that will be glued.  Make sure you don't get any primer or glue on the threads of the cleanouts.  Now take the PVC cement and put it on one joint at a tome.  Meaning you put it on the joint then assemble it right away.  Then go on to the next one.  Just a couple notes.  Use a hammer to make sure the barrel is all the way back in the reducer.  Make sure all parts are fully pushed together.

Cardboard Wadding

To make this work you might want a drawing compass to help you cut the circles.  If you don't have one you can take a piece of cardboard and put it up against the barrel and trace around it.  So which ever you choose to do make the circles 4" in diameter.  You can use scissors to cut them out.  Keep them close in size.  Make 2 or 4 of these.  Tape them or hot glue them together.  That should be your wadding.    Sand the edges a little for better performance.

IMPORTANT

You can power this cannon with a BBQ igniter or use my Pneumatic Add-On.  Both ways are very impressive.  You can see the differences below.  Let me know if I can help you out at all