Triggering a Projectile

[MysticHaste]

Okay here is what is going on, in order to simplify this I'm going to put it into an Era style context.

I have a gun, when I click it on the ground I want it to shoot at the mousex/mousey, but when it reaches its target x/y i want it to explode, as if it has hit the ground.

(Imagine shooting a rocket at the ground in order to to explosion damage instead of a direct hit)

Is there a way I can change a projectile onces its fired, or will this require a complex equation to work out the exact gravity needed to get the projectile to hit the ground on said position?

Thanks for help in advance.

-MH/Dlaiyre Rain.