problem on switching gun (a var don't turn true)

The second script Allows you to change 3 different weapons, the first allows the operation of one of the three weapons (the shotgun). My Problem Is That if the var shot (sorry, I use Italian names for var because I'm Italian), do not become true before I change my weapon, then when I get back on the weapon "Shotgun", I can not shoot because the variable is false. My question is: How do I return the var true all the time I select the weapon "Shotgun"? Thanks

 // prefab that i want to shot
 var prototipoProiettile : Transform;
 
 // energy that iI want to apllicate to the prefab that i create
   
 var energia : int;
 
 //if the "bullet" is or isen't ready for shoot
 var colpo : boolean = true;
 
 
 //recharg sound
 var otherclip : AudioClip;
 
 //shoot sound
 var audio1 : AudioClip;
 
 //The Shotgun Ammo
 var munizioni : int = 16;
 var munizioniMax : int = 16;
 
 
 // Ammo Display 
 var ammodisplay : GUIText;
 
 
 
 function Update () {
 ammodisplay.text = "Ammo= "+ munizioni;
 
 //If i clic the mouse, the "bullet" is "ready for shoot" and I got enaugh ammo
 if(Input.GetMouseButton(0)){
 if(colpo == true && munizioni > 0){
 spara();
 }
 
 
 
 }
 }
 
 function spara (){
 
          
 
           var istanza : Transform;
 //create the "bullet" using the prefab
           istanza = Instantiate(prototipoProiettile, transform.position, transform.rotation);
 //Add the "speed" to the "bullet"
 istanza.rigidbody.AddForce(istanza.transform.forward * energia);
  //Play the "shoot" sound
  audio.Play();
  //The "bullet" now isen't ready for shoot(so i can't shoot)
  colpo = false;
 
 munizioni--;  
   yield WaitForSeconds(1.4);         
 
 audio.clip = otherclip;
 //Play the reloding sound
 audio.Play();
 yield WaitForSeconds(audio.clip.length);
 
 //Now the bullet is ready for shoot(so i can shoot)
 colpo = true;  
 
 audio.clip = audio1;     
 }
 
 
 //This is for "pick up" the ammo on the ground
 
 
 
 function OnTriggerEnter(other : Collider) {
 if (other.CompareTag("ammoshotgun")) {
 munizioni = munizioniMax;
 Destroy(other.gameObject);
 }
 }

the wepons switch script:

 public var pistola : GameObject;
 public var shotgun : GameObject;
 public var mitra : GameObject;
 
 
 function Update () {
 
 //Select Pistols
 if(Input.GetKeyDown("1")) {
 pistola.SetActive(true);
 shotgun.SetActive(false);
 mitra.SetActive(false);
 }
 
 //select shotgun
 if(Input.GetKeyDown("2")) {
 pistola.SetActive(false);
 shotgun.SetActive(true);
 mitra.SetActive(false);
 }
 //Select Uzi
 if(Input.GetKeyDown("3")) {
 pistola.SetActive(false);
 shotgun.SetActive(false);
 mitra.SetActive(true);
 }
 }

Thanks! (and sorry if my english isen't very good :/, because i'm italian)