Way to have an object only destructible when hit with the FirstPersonProjectile?

I’m using UE4.14 at a beginner level, and I’m trying to make a cube crumble when shot with the first person projectile of the beginner FPS. I’ve already taken the mesh and fractured it, but when compiling the code, I get an error about the Cast To first person projectile.
What I have in my blueprint currently is this: