Minecraft fireworks in dispensers?

I'm trying to make a firework show on minecraft 1.7.4. I have watched many videos on different ways people have done it. The problem I'm having is when I put the fireworks in a dispenser and then run a redstone signal to it, they don't shoot in the air, they just drop out of the dispenser to be picked up again. I have tried numerous ways of doing this and different signal setups, but every time they just fall on the ground. What am I doing wrong?