One day late:
Duration: 1 round per caster level
The caster is able to fling one magical stone each round at a target. A normal to-hit roll (DEX missile adjustment applies) must be rolled. Each magical stone does 1d6 damage.
If the caster suffers damage after the spell has been cast but before it expires, he or she must roll a saving throw vs. spells to avoid losing the remaining duration.
Shorter range than a magic missile and requires a to-hit roll, but the multiple shots make up for that. A simple alternative.