1: Dont overpressurize the cannon, a fitting popping off at low pressre is not as dangerous. Since it LOOKS like ABS (solid black pipe) not PVW (white pipe) its not rated for pressure, the benefit from ABS is that the pipe will not typically shatter like PVC so if it does get hit under high pressure it typically rips lengthwise with the pipe/fittings, where PVC will shatter.
2: Probably should fire it from a distance, make a little project box from parts at radio shack : three 9v batteries w/ clips, a pushbutton switch and a long cord, or pneumatically modify the valve and add a long hose and ball valve at the end to fire it.
3: IF you do have to drill and tap a fitting into air chamber do it over a fitting where the fitting and pipe overlap, this will give the threads more plastic to grip, also use teflon tape on the threads.
So before any of these dink heads chew you out for using DWV they or I should explain to you why NSF-PW parts are safer. NSF-DWV parts are intended for draining water from your toilet, sink, or shower and are not intended or rated to hold any pressure. NSF-PW parts have a tighter fit and have a longer depth to hold more pipe surface.
The design of the two fittings look different in apperance
NSF-PW fittings typically look streamlined, no pipe stops are visible on the outside (they are on the inside)
NSF-DWV fittings have a shorter area to grip the pipe and the pipe stops are visible from the outside and inside of the fitting.
The cannon looks overall pretty nice, you butted the two elbows pretty close together, not bad for your first cannon. Maybe throw a cool paint job on it, pimp it out with some neon lights
