I found this out when i was trying to shoot ammo with sparklers attached. I did not add any fuel and i glued the gun together months ago but still resulted in a large 'bang' and more recoil then usual.
You will need:
A pneumatic cannon
Sparklers Or some thing that will burn in an enclosed space for a short time
Fuel
How to
1. Stick sparkler in back of ammo. You can protect the inside on the barrel from the heat of the sparkler by cutting up a aluminum can then putting the rolled up metal inside barrel.
2. Spray your fuel in to chamber though ball valve
3. Close up chamber, and pressurize
4. Light sparkler, stick ammo in to barrel (if Breach loading light sparkler when ammo is already in barrel)
5. Quickly turn ball valve to avoid more barrel damage from sparkler.
Tips/safety:
Do not use lots of fuel
Do not use high pressures
IMPORTANT: Turning ball valve too slowly might lead to chamber exploding

Would it be safe to try to repeat this? if so how much fuel and pressure should be used?
p.s I take no responsibility if you explode trying to do this. Sorry far any grammar or spelling mistakes.