A quick one

[Demonic69]

I can't see a problem with it. They're not restricted chemicals, yet, and you're not making an explosion with the intent or possibility to harm, so long as you do it safely and make sure you dispose of everything you're not using properly I think you'll be fine.
You could always ask on the pyro society.

[Mattnall]

Sharpshooter, do you need some video of a home made cannon firing? I can send you some if you do.

We made some at a class and they worked fine, even managed to get some small carriages designed and made using a laser cutter and MDF for a full project. Just had to be on the RFD/FAC when we tried them out.
These were approx 6" long and fired a patched 30cal ball or bullet from an 8mm bore. One smaller version fired 6mm BBs that left a nasty dent in some dry wall targetry.

[$harp$hooter]

Matt,

That would be great if you could. It would be a nice addition to his project to have some actual footage to back up his theoretical material. Will drop you a PM.

Cheers