Collider not detecting any collision :(

I have a bullet and a enemy. Both have colliders. I have used the same code for the player bullet hit and it works but when i copied and pasted 90% code of the same script, the enemy bullet doesn't detect any collision, neither with player nor with any other object.

here is some code-


using UnityEngine;
using System.Collections;

public class EnemyShootingBullets : MonoBehaviour {

public float speed;
//explosion or vibration or spark or anything that enemy bullet impact would make on the player
public GameObject Explosion;
//the box surrounding the city as a boundry limit to player(may not for the enemy)
public GameObject cityBoxSquare;
void Start ()
{
//Physics.IgnoreCollision(cityBoxSquare.collider, collider);
rigidbody.velocity = transform.forward * speed;
Destroy(gameObject,10);

}

void OnCollisionEnter (Collision col){
Debug.Log("Enemy bullet hit something");
string nam = col.gameObject.name;
if (nam == "Peterling"|col.gameObject.tag == "Player") {
Debug.Log("Peterling hit");
//call a function from game controller script to reduce player health






ContactPoint contact = col.contacts [0];
Quaternion rot = Quaternion.FromToRotation (Vector3.up, contact.normal);
Vector3 pos = contact.point;
Instantiate (Explosion, pos, rot);
Destroy (gameObject);

}
}

}



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additional info-

none of the collider is on trigger selected.
The same code was working for my player bullet hitting the enemy.

ANY SUGGESTION WOULD BE APPRECIATED.

 

Experiment by changing rigidbody's "sleeping mode" to "never sleep".

 

Very Project Settings -> Physics to make sure you hadn't turned off collisions between the layers of your bullet and your enemy.