what about ammonium triiodide crystals? isnt that what the use in those snap and pops? when i was a kid we unrolled a couple of boxes of those and filled up the nose cone of a model rocket and used a steel pipe to make a "rocket launcher" and fired it at the side of dads old shed.... it punched a hole in the side of dads metal shed the size of a soccer ball... dad was none too happy about it...lol... but we still laugh about it today...
check out this link, they tell you how to make it...
http://www.skepticfiles.org/new/195doc.htm
or...if you need impact explosive what about tannerite? just brain storming here...