I looked at this topic and thought it was awesome, so it got me thinking, if I were to use bottle rockets for ammo for the SPNKR, which would fly straight and explode! Obviously if I make this I will have to take multiple things into consideration. For instance, pvc will have to be used for straigh trajectory, and I could only fire it straight in the air, because frankly it is an explosive and could hurt someone, and how to make it fire. Well, I am a pyro so I know a thing or two about explosives. Instead of lighting outside the tubes which is dangerous because of fuse length, I would dissasemble a lighter, one of those long ones used for grill lighting, you know what im talking about, the one with the "barrel" and keep the fuel in a separate part of the launcher due to explosions not wanted. So I would take the barrel and attach it to the pvc with the rocket which would be loaded from the front of the launcher. There would be 2 lighters so I can fire either when I want. Sounds pretty good, I guess I just have to look into designs now!
I've done potatoe guns before. A BBQ clicker/igniter works great, throws a wicked spark, and deasel starter fluid/ether is a great propellant. I shot a potatoe 200+ yards doing that (on the really conservative side, my dad said almost 1/4 mile, but I'm skeptical).
@f0xtr0t09 - If you use bottle rockets, you need to keep the stick on them, so fit the PVC so the whole thing shoots through. I tried taking the stick off and shooting them like a gun, didn't work so hot. They just went end over end after they came out, and if you don't have the pipe perfectly straight, they get stuck and explode inside. Its scary (speaking from personal experience).
So I would say try and stick to the potatoes. Less chance for injury. If you are looking for red smoke, did you think about putting some red marking chalk in the combustion chamber? The convection/suction should carry it through igntition and launch and give you some of the effect you are looking for. Just a thought.