Strike Anywhere matches!
You know the type, wooden with a white tip that you can strike on any rough surface. The kind kids are generally banned from.

Take a handful of them and carefully cut off the white part from the tip. Get a 1/2" bolt and its corresponding nut and twist the nut on just enough to hold onto the bolt. Put five match heads inside the nut. Twist a second 1/2" bolt onto the other side of the nut until it's snugly pressing against the match heads. Drop it bolt first onto a concrete sidewalk.

Run before irate parents come outside to investigate the sound of a gunshot.
( The Resident Loon Not a demographic. Do not measure., Fri 10 Aug 2012, 16:48, 3 replies)

We used to do that with
rolls of caps.

Don't know if you can still get them - the (normally red) paper strips that went into cap guns.

Tear about 10 of them off the strip, roll them up and put into the bolt/nut contraption. Throw it up in the air, gives a good bang.
(username failed moderation, Fri 10 Aug 2012, 17:07, closed)

We used to play with those too,
I found that a magnifying glass in sunlight could set them off without touching them. Better: if you tear them so that the paper is long on one side and right up against the little round dot on the other, they fly. We used to launch them at each other from about a foot away. Completely harmless and good for an hour's laughs when you're nine years old.

Unfortunately a neighborhood kid discovered that if you dunked a whole roll of caps in gasoline and used the magnifying glass to set one of them off the entire thing burst into flame and shot bits of burning paper everywhere. He got caught and playing with magnifying lenses got banned.
( The Resident Loon Not a demographic. Do not measure., Fri 10 Aug 2012, 18:10, closed)

Takes me back .
Me and my friends used to do this ,using redhead matches,must have been about 40 yrs ago,we also used to bunch a few matches together, wrap the heads in silver foil and heat them watch them explode...........happy days.
(andycrass loves two hats on, Sat 11 Aug 2012, 12:23, closed)