Powder Toy is a universe with its own set of rules. If you want something strong enough to break iron, whip out the EXOT or build a fusion lobber. Most of the explosives are materials that aren't strong enough to blow stuff up without a lot of careful work, they're basically just volatile materials.
I edited the properties according to the suggestions so far.
What about something that doesn't explode per say,but cuts into things? like you set a pixel next to a nice tough TTAN, QRTZ, SHLD, wall and you set it off, maybe from SPRK or IGNC, and it makes a nice 1 pixel line of NONE into the wall and create a little pressure and enough heat to make METL glow, and voila, you have a nice interseting "explosive"
Ummm..... So, anybody out there want to add EXL1 and EXL2to their TPTmod?
The basic idea is this:
2 elements that are completely stable on their own, but violantly react when mixed together.