Thank you for putting in clearer terms. The "explosive" effects that have been eluded to are from the containing of the great expansion of gas. This is what makes gunpowder a good propellant. Under scientific definition this is not an explosion. It could be defined in simplistic terms a Low Explosive.
As my colleague has explained a white metal case would have "glued" the iron balls together. Melting of the white metal. It would have come out in one lump.