Material keeps unloading

Hi guys. My bullet prefab has a material assigned. After I Test-Play the game its material resets to none. Have to reassign it each time before new Play-test. Any ideas?

 function Fire()
     {
         var bulletfire = Instantiate (bullet,gameObject.Find("muzzle").transform.position,Quaternion.identity);
         bulletfire.rigidbody.AddForce(transform.forward * 500);
         bullet.renderer.material.color = Color(1, indG, indB);
         var bulletShellFire = Instantiate (bulletShell,gameObject.Find("Cylinder12").transform.position,Quaternion.identity);
         bulletShellFire.rigidbody.AddForce(transform.right * 200);
         roundOut = true;
         Timer();
     }