Citric Acid Grenade
What you need:
-Flimsy water bottle (Standard size) - (i think .5L)
-Citric Acid (perferably a lot) - (hard to find)
-Baking Soda (more than citric acid) - (cheap)
-BB's (anywhere from 50-150)
Ok pour about 6 tsp. of baking soda into the water...