For mine I'm doing what the first link has, but using a paintball gun instead of a special 203 shell.

I wonder if you could drop one of those down a tube with a button on the bottom that would fire the shell?

The first link may work, the range scares me even after modifying it. Thanks

The only problem is how are you gonna get the button to be pushed with enough force?

For foam rockets try milsim labs on Facebook... They fit perfect in a 40mm tube Got around 300feets on a propane Shell ( and CO2 Shell partiaĺly destroyed the rocket )

I've had some not so pleasant Propane experiences... Would greengas work? It shoots around 100fps lower than CO2 from what I've heard.

Green gas is basicly propane with silicone oil in it... ...

First it depends on what PSI you've jazzed the shell with. The hotter it is the harder you have to hit it.

Second you'd want to add a sleeve as it's rim cartridge that would go cockeyed in the tube.

Third you'd need a breech or you'd have to dump the tube upside down to remove the spent half.

Now the whole math behind a hand held tube with no sights is you pop off a round and see where it lands. Then you correct your aim or your charge.

If you pick up the tube every shot and do the hokey pokey you won't be able to walk the rounds on the target.

With the more sophisticated systems you'll have the traverse and elevation locked down and click adjustable and you'll have your dope so first shot on target is doable

For airsoft launchers body english is where it's at.

Now if this is just an atmosphere piece and you don't want to send a projectile down range just fill it with glitter or flour and get a decent pop and puff out of it.