How can I decrease accuracy when the gun is fired?

Hi everyone!

I would like someone to tell me how to make the accuracy of the gun decrease when it is fired. The part that fires the raycast is "var ray : Ray = Camera.main.ScreenPointToRay(Vector3(Screen.width*0.5, Screen.height*0.5, 0));" and "if (Physics.Raycast (ray, hit, 500))". The rest just instantiates a bullet effect. I know that Haim96 answered a similar script, but I didn't make it clear enough to him. Thanks, Stormy102

 #pragma strict
 
 var Effect : Transform;
 var TheDammage = 100;
 var gunshotSound : AudioClip;
 var reloadGrenade : AudioClip;
 var ammoCount : int = 10;
 var totalAmmo : int = 120;
 var reloadTime : int = 3;
 var reloadAmount : int = 10;
 var ammo : GUIText;
 var gunName : GUIText;
 var fireRate : float = 3.0;
 var bulletHole : Material;
 var force = 10;
 private var nextFire : float =0.0;
  
 function Update ()
 { 
     Fire ();
     Reload();
     OnGUI();
 }
  
 function Fire () {
  
     if (ammoCount > 0) {
  
         if (Input.GetButtonDown("Fire1") && Time.time > nextFire) {
  
             nextFire = Time.time + fireRate;
  
             InstantiateGrenade();
  
             ammoCount -=1;
  
         }
  
     }
  
 }
  
 //---------------------------------------------------------------------------------
  
 function InstantiateGrenade () {
     var hit : RaycastHit;
     var ray : Ray = Camera.main.ScreenPointToRay(Vector3(Screen.width*0.5, Screen.height*0.5, 0));
     
     if (Input.GetMouseButtonDown(0))
     {
         AudioSource.PlayClipAtPoint(gunshotSound, transform.position, 1);
         if (Physics.Raycast (ray, hit, 500))
         {
             var particleClone = Instantiate(Effect, hit.point, Quaternion.LookRotation(hit.normal));
             var hitRotation = Quaternion.FromToRotation(Vector3.up, hit.normal);
             Instantiate(bulletHole, hit.point, hitRotation);
             Destroy(particleClone.gameObject, 2);
             hit.transform.SendMessage("ApplyDammage", TheDammage, SendMessageOptions.DontRequireReceiver);
         }
     }
 }
  
 //---------------------------------------------------------------------------------
  
 function Reload () {
  
     if(ammoCount < 1 && totalAmmo > 10) { //if we have less than 1 bullet then we can reload
  
     if(Input.GetKeyDown("r")) {
  
         AudioSource.PlayClipAtPoint(reloadGrenade, transform.position, 1);
  
         yield WaitForSeconds(reloadTime);
  
 ammoCount += reloadAmount;
  
 totalAmmo -= reloadAmount;
  
 }
  
 }
  
 }
  
 //---------------------------------------------------------------------------------
  
 function OnGUI () {
  
 ammo.text = "Ammo: " + ammoCount + "/" +  totalAmmo.ToString();
  gunName.text = "Lee-Enfield Mark III";
 
 }