Ammo Pick up C# Not Working?

I'm trying to make it so that when the player collides with the ammo pick up (Rocket Ammo) the code adds 5 extra rockets and destroyed the ammo pack.

However, in its current state, it only activates if I hit the pick up on the perfect angel normal just hitting its side or corner?

I have Riggedbody attached to both objects but still nothing.

Code:

     void OnCollisionEnterEnter (Collision col){
         if (col.gameObject.tag == "RocketAmmo") { 
             Rockets = Rockets + 5;
             AudioSource.PlayClipAtPoint (Pickup, col.transform.position);
             Destroy (col.gameObject);
         }

EDIT: - FIXED -

I seem to have fixed it by changing :

 void OnCollisionEnterEnter (Collision col){

to :

 void OnControllerColliderHit (ControllerColliderHit other){