How to make bullets pass through each other.

Hi, I am making a simple two player tank game similar to a game called tank trouble. The bullets are able to bounce off of other objects including copies of itself. How do I make it so that the bullets can go through each other, but still be able to bounce through other objects? This is my script:

using UnityEngine;

using System.Collections;

public class BulletScript : MonoBehaviour {

 public int range = 200;
 private GameObject player1;
 private Vector3 oldVelocity;
 public Rigidbody rb;
 public GameObject bullet;
 
 void Start () {
     GameObject Player = GameObject.Find("Player 1");
     Shooting playerScript = Player.GetComponent<Shooting>();
     rb = GetComponent<Rigidbody>();
     rb.velocity = playerScript.m_FireTransform.forward * 15;
     rb.freezeRotation = true;
 }
 void Update () {
     GameObject Player = GameObject.Find("Player 1");
     Shooting playerScript = Player.GetComponent<Shooting>();

     if (range < 0) {
         Destroy (gameObject);
         playerScript.ammo += 1;
     }
     range --;
     oldVelocity = rb.velocity;
 }
 void OnCollisionEnter(Collision collision){
     ContactPoint contact = collision.contacts [0];
     Vector3 reflectedVelocity = Vector3.Reflect (oldVelocity, contact.normal);
     rb.velocity = reflectedVelocity;
     Quaternion rotation = Quaternion.FromToRotation (oldVelocity, reflectedVelocity);
     transform.rotation = rotation * transform.rotation;
 }

}