Set the projectile's arming delay to less than the lifetime. Then, set "isBallistic" to false. This will make the projectile stay in the ground when fired and disappear later.
If you want an impact explosion, create an explosion datablock that will be the impact, and in the projectile datablock add this:
bounceExplosion = <name of the impact explosion>;
The normal explosion is like when the arrow vanishes. Unless the projectile is supposed to explode after going into the ground, you dont want it to do any damage.
Hope this helps you.