The powder is a good idea. We will have to try that with the melon musket someday when we want a smokey looking photo.
It takes a big yard to play with a "tater" gun. We have problems finding empty places big enough to launch watermelons 1/2 mile or more.
There's just something missing here.. Or maybe it's that there's too much here.. clluttered background. This really could have benefitted from a much shallower DOF, and more emphasis on the cannon itself.