How do I set an art effect to wait until the projectile hits

[Fell_Paladin]

How do I set an art effect to wait until the projectile hits, ie having an explosion go off when a cluster missle hits (in addition to the normal one). What I am ideally tying to do here is have 1 cluster missle launch and when it hits have a big explosion go off. I have a model, but no matter where I place the art effect it never waits until the missile hits before blowing up. Help please!