The best method from experience and yea ,I am a pyro like no one knows and I love to mess with homeade ish all the time.

2 liter bottle, HOT HOT Scalding hot water bout half way filled up and take a 1 pound block or less of dry ice, put it in a towel or rag and lay it on a hard table that u wont break or on the concrete and smash the ice into oblivion with a hammer inside the towel. This will make the ice much easier to get into the bottle and more surface area = quicker expansion of C02. Empty it in with a paper funnel if you can then close it quick and dont even throw it, just leave it and within like 40 seconds you have a huge explosion from it.

Use the hottest water and most surface area u can get from the ice.