Well @Primpy, @Sir Ementaler is right, there were two charges by the rock.
But, yeah, I too feel that the explosion effect is a bit off. Unreal 4's Cascade particle system is amazing, but translucency is the weakest point of the whole engine. And the smoke is translucent.
Maybe this version is better(?):

It's fun to launch Jazz, gaussgun-like:


Any opinions on the proximity bomb idea?