Why do you need it to shoot 1/4 mile?

yeah there is no way you will be able to hit withen 20-50ft of the person at that distance. We use combustion cannons as mortars and ive gotten hit by them. THe point of mortars in airsoft/paintball is not to hit the enemy, but to force the enemy into cover ...

wow, over here in the good old free usa, I dont worry about anyone searching me with my spudguns, anyway, where I live, a cop drives down the road about.......4 times a year (no joke!) I live WAAAAAAAAAY out in the country.
I live i a small town, and the popo drive by all the time except the 2 ...

I know this is a little off topic, but you could take a ziplock bag, pour flower in it and wrap with rubber bands. this would create a white phosphourous kind of effect when it lands.