Highly volatile 2 compound explosive composed of ammonium nitrate oxidizer(fertilizer) and hydrazine (rocket fuel).
Because it has been widely referred to as the "world's most powerful non-nuclear explosive" and the rocket fuel is highly toxic it's not very often used.
It's expensive, hard to disarm and there are many cheaper and safer explosives on the market.
So it's generally seen as a bad idea.

But these hunter guys are a bunch of extremist and this was their end game winning stroke.
Too bad for them the game has changed.

Now the question is: what is Matt going to do with this info? Is he going to tell Magnus and use the thing together? Or is he going to send Magnus the key and leave the state to watch the explosion trough binoculars?