[ashark]

Back when I did this a few times a year, 20oz soda bottles made the best boom. 2-liter bottles couldn't take as many PSI and water bottles... well, they're not designed to contain pressure. They'd fail at the cap, usually.

That may no longer hold, since 20oz bottles feel flimsier these days and all have low-profile caps. Haven't tried in a while.

Also, PVC pipe burried in ground, drop dry ice bomb in, drop another bottle with some water in it on top = dry ice mortar. Those little plastic bubble things that toys in vending machines come in? A little dry ice, a little water, close it, place lid down. POP, the bubble part flies a meter or so in the air.

I will note for anyone trying this that the parent's ratios are very different from what I used. Crushed dry ice to 1/10-1/8 full, about twice that much water. Unusually warm water (say, from near the surface of a pond or lake in late August) will greatly reduce time-to-boom, so beware. Too little water and it'll freeze before boom, greatly delaying or even preventing it. Very annoying. Attaching to something heavy (but NOT shrapnel-genrating) and sinking in ~5-10 feet of water is fun. Huge bubble, explosion can be felt on land nearby.