I am trying to make guns accurate by adding in a "Random.Range" referenced added to the "Vector3" direction my player is facing. Yet, I am unsure of how to do this.

function Fire() {
   if (Time.time > reloadTime + lastShot && clipsize > 0)
   {

      if (abletoshoot == 1) 
      {
         BroadcastMessage ("ShootAnimation");

         var instantiatedProjectile : Rigidbody = Instantiate (projectile, transform.position, transform.rotation);

         instantiatedProjectile.velocity = transform.TransformDirection(Vector3(0, 0, initialSpeed));

         Physics.IgnoreCollision( instantiatedProjectile.collider, transform.root.collider);

         lastShot = Time.time;
         clipsize--;
      }
   }
}

Im not sure where to put in "Random.Range", and how to set the range etc., while still keeping the same parameters. Is anyone willing to show me how I could perform this?