This is going to to be my Idea page, where my many ideas that probably won't ever be built by me, can be shared with all of you, if any of you decide to build anything like this just let me know how it works, if it works.

Pneumatic London gun
Have you ever heard of the London gun, its a huge cannon that Germany built towards the end of WWII that used mutiple chambers along the length of the barrel. as the projectile passed another chamber the flame front from the previous chamber would ignite the propellent in that chamber thus keeping overall pressure down and not having to use a large powder charge at the start and blowing the gun to pieces.
A pnuematic london gun would have to have 2 or more air tanks with valves that could be activated electricly. The first tank and valve would act just like a normal pneumatic, but you would have a phototransistor in the barrel to signal the second valve to trip thus releasing the air in the second chamber. I'm not sure if this would provide any performance gains but it would allow you to use a longer barrel and several small chambers spaced along the length instead of a large chamber, and it would allow a fragile projectile to be accelerated gradually instead of violently. There would be alot of possibilities to tune it, like delay in releasing secondary air and different pressures in secondary and primary air tanks, as well as volumes. Maybe high volume low pressure in primary and low volume high pressure in secondary.