Simply cut up scrap paper and put it in the open end of the dart
And FIRE, a shower of confettie upon your victims.
Buy a lazer at the doller store or something, and tape it on your tube. You will want to look in the tube and make sure that the lazer beam is in the middle of the tube so that it is accurate
Buy a flashlight and tape it on the tube, your tube should be strong to hold this. like the lazer, align the flashlight with the tube