It could have been black powder or black powder substitute. It could have been tannerite (exploding targets binary explosive - legal). It could be a homemade explosives and those are not difficult to make. Gunpowder functions as a high explosive when confined or initiated with high energy.
We can’t make the world bulletproof and government can’t fix the evil in the heart of man beyond removing evil from society. Too many Americans fail to grasp the truth of that statement.
It wasn’t black powder or BP substitute. Not enough oxides left on the components, not enough smoke from the blast and the fire ball doesn’t look right.
I have shot it for 15 or 20 years and it definitely not black powder.
And it wasn’t tannerite.
The Psi limits of the pressure cooker are very low compared to the breech of a gun and with the damage the exposive would seem to have to be something with a lot of speed.