I have some problems to use OnCollisioEnter between 2 RigidBodys

hello, i need a little help,pleaseeeee…I just try to do OnCollisionEnter between 2 Rigidbodys:I have a shooter who instantiate a prefab and also a player who instantiate a prefab, also. When i try to do the Collision between the prefabs,Unity doesn`t red"OnCollisioEnter".My prefabs are BoxCollider and RigidBodys. My script:

using UnityEngine;
using System.Collections;

public class aruncator1 : MonoBehaviour
{
    public GameObject prefab;
    private GameObject shooter;
    public float time;


    // Use this for initialization
    void Start()
    {

    }

    // Update is called once per frame
    void Update()
    {

        time += Time.deltaTime;

        if (time >= 3)
        {
            Debug.Log("merge 1");
            time = 0;
            shooter = Instantiate(prefab, transform.position, Quaternion.identity) as GameObject;
            shooter.rigidbody.AddForce(Vector3.down * 2000);
        }
       
      
    }
    void OnCollisionEnter(Collision shooter)
    {
        Debug.Log("coliziune");
        if (shooter.rigidbody)
        {
            Destroy(shooter.rigidbody);
        }
    }
 
}

i try to do with this, but the problem is that “void OnCollisionEnter()” is never read…

 void OnCollisionEnter(Collision something)
    {
        Debug.Log("collision");

        if (something.gameObject.tag == "bullet")
        {
            Debug.Log("tag Player");

        }
    }

when i press Play, OnCollisionEnter is not detected…(Debug.Log(“collision”); - does not appear in console)