I do belive that in the projectile datablock theirs two fields that change that, I think they're called bounceElastics and another, I don't know without looking.
bounceElasticity = 0.5;
bounceFriction = 0.20;
I don't know if that's it but, It looks likely.
That would be part of it, make Elasticity a higher value than Friction, or set friction to 0.0 and elasticity to 0.99 for maximum bounceage each time the projectile bounces off of something. In this case, it will have a bouncing power of 0.99 - 0.0 = 0.99, and so when it bounces it will retain 99% of it's initial Before-bounce velocity after the bounce.
also set
isBallistic = false; //to true
You need this to get the projectile to bounce and become effected by the GravMod value.
and so, set gravitymod right underneath to a positive non-zero value to get gravity acted on the projectile
Finally set Fadedelay to a higher value than Lifetime (example, fadedelay to 4500 and lifetime to 4000)
You can also set Armingdelay to whatever value, this effects how long the projectile will be bouncing, and once it runs out the next thing the projectile hits will set it off.
for a projectile that explodes when it's lifetime runs out, add the following code within the datablock
Explodeondeath = true;
So when the lifetime of the missle/projectile runs out, it explodes.
This is all in your ProjectileData Datablock by the way.