I'm pretty clueless about what you need. Maybe some more details about the cannon might help. There are some pneumatically minded guys around here who will likely chime in. The only thing I really know how to do is make a piston cannon. Sounds like you want to buy a valve, but I can't think of any p...

There is an external ballistics calculator in GGDT in which you can either choose to use a specific barrel angle, or calculate the angle for maximum range. You can also enter the coefficient of drag.

I looked at the GGDT program and it doesn't appear to have an option to calculate the maximum range in which it will be able to fire which is in my opinion the whole point of the software.. The point of the program is to have an idea of what your muzzle velocity will be. As for maximum range, that ...