Particle collider not working

i have a fps game with particle for bullets and everything i do i still cant get a message to appear when the particles collide with the enemy. send collision messages are on for both the particle systems and for the world particle collider. This is my basic script so far... can anyone tell me where im going wrong? using UnityEngine; using System.Collections;

public class ParticleCol : MonoBehaviour {

 void OnParticleCollision (GameObject other){
         print ("Collision!!!");
 

} }