Well, I guess Google has proved me wrong once again.  I went shooting tonight at dusk and the cannon was working really well.  I had to glue in my protective cap that isolates the handle with the electronics from the combustion chamber.  Now that I eliminated that source of pressure loss we get a consistent 200 yards out of it 
 
Technician1002 wrote:I gotta try a rifled barrel.
Me too!  I've been lusting after one of those clear PVC ones for a long time now...
Oh and a cool thing I found out, even though the barrel PVC is white, at night it glows bright orange during the launch.  I never noticed that during the day...wish I could capture it on film.