The bbq sparker will not ignite the powder in the engine, its not enough to heat it up to chemically react with the air. I made a black powder cannon b4 and tried to ignite it with a sparker, and it didnt work at all, i also tried it on a model rocket, same deal. If you just ignite the rocket engine, and make sure you have some kind of combustible gas in the chamber, it will lite the chamber with the thrust from the engine. How far will it go? probebly not too far. if your lucky, it will even go strait. they do that kinda stuff on battle ships and subs, and torpeados kinda work the same, but there not rocket propelled. the chamber is pressurized (like when a spud gun chamber ignites) then the missle is lauched out the top, were it then ignites and with its fins controlling it, goes in the direction it needs to. how you could do this with a spud gun is beyond me, but when or if you do, tell me, it'd gotta be pretty damn cool.