Making projectiles disappear

I'm currently working on a mod where we have a projectile that bounces off whatever it hits multiple times before settling. Obviously this creates problems with a skybox and I was wondering if anyone knew a way to make a projectile disappear when hitting a fake backdrop?

Many thanks

many thanks... I'll give it a shot

Yes... that it did. Actually, since I have your attention... I'm having issues with putting two seperate water volumes next to each other. What I'm attempting to replicate is a tide that pushes you in from the water on to my beach. There is no problem doing this with the first volume, but in the second where want the player to be brutally forced into the first I cannot enter unless i enter the volume from above. Any ideas?!?

THanks again!