The chamber is made from two bottles of Walgreens brand robitussin. The bottom of one of the bottles was cut off and then the two bottles were hot glued and taped together with some electrical tape. Ignition comes from a BBQ ignitor, installed on the cap of the back bottle.
The barrel is a 1/8" x 6" threaded brass pipe, which was filed down on one end and hammered into a 3/8" threaded brass hex nipple. And to make sure it sealed, I put some more hot glue around the back of the barrel where it goes into the 3/8" fitting. The 3/8" nipple threads into the end of the second pill bottle, and, since I'm a hot-glue fiend, I put some more hot glue around the joint

I might put a longer barrel on it, since the C:B ratio is pretty bad right now. Performance would probably look a lot better.
Anyways, enough talking. Here are some pictures:
<a href="http://i119.photobucket.com/albums/o139 ... .jpg"><img src="http://i119.photobucket.com/albums/o139 ... G_2323.jpg" height="200 " alt="Overview of the cannon"></a>
<a href="http://i119.photobucket.com/albums/o139 ... .jpg"><img src="http://i119.photobucket.com/albums/o139 ... G_2325.jpg" height="200" alt="The ignitor"> </a>
And a short <a href="http://s119.photobucket.com/albums/o139 ... ">video</a>...