Note

      All pipe and fittings are schedule 40 PVC

Parts

• 1 1/2" pipe 72" long

• 3" pipe 36" long

• 1 1/2" to 3" bell reducer

• 3" female adapter

• 3" cleanout plug

• Diaphragm (see below)

• A couple old trouser legs

• Source of compressed air

• Blow gun with tapered nozzle (What's a blow gun? It's a valve/nozzle combination that attaches to a compressed air hose.

• They're commonly used in machine shops and garages to blow dust away.

• You can usually find one at most autoparts stores.)

Assembly

• Cut the pipes to length. The barrel pipe must have a perfectly square and smooth surface on the breach end. You may have to flat file and sand it to make sure a good seal with the diaphragm is achieved.

• Cut a 3 3/16 diameter disk of 3/32 thick polypropylene or polyethylene. A cheap dishpan from Kmart may be a good source of diaphragm material.

• The front bell reducer has a small ridge that would prevent barrel from being pushed through it during assembly. Use a half round file to remove the ridge. Make sure you can push the barrel though the reducer. Remove the barrel and set it aside.

• Drill a hole through the center of the cleanout plug. Size this hole to achieve a tight fit with the tapered nozzle of the blow gun.
  Assemble the outer chamber first. Glue the bell reducer and the female adapter to each end of the 3" pipe. allow the glue to dry before proceeding to install the barrel.

• Lace the diaphragm in the female adapter and screw the cleanout plug in firmly. Push the barrel through the reducer until it sets firmly against the diaphragm. Pull it back out 3 inches to allow glue to be applied. Apply glue to the barrel in front of the reducer and push it quickly back into position against the diaphragm. Hold the barrel in place until the glue dries.

• After the gun is assembled, remove the cleanout plug and check to see if the barrel is properly centered in the female adapter at the breach. If it is not, cut 3 or 4 pieces of 5/8" heater hose about 1" long and force them between the barrel and the outer chamber.

• Slip the old trouser legs over the chamber area of the cannon and tape them in place. This simple precaution will contain any pieces of exploding pipe from becoming shrapnel if something should go wrong.

Firing

      To fire the cannon, unscrew the cleanout plug and remove the diaphragm. Push a pre-cut spud into the breach of the barrel, making sure it is an inch or two below flush. Replace the diaphragm and screw the cleanout plug in firmly. Point the cannon down range. Place the blowgun in the charging hole drilled centered in the cleanout plug. Start squirting air into the cannon with the blowgun. When the sound of hissing air quiets down or stops, the cannon is charged and ready to fire. Keep the blowgun valve pressed down. Aim carefully and pull the blowgun from the charging hole.