Gun with ammo help

I need help with my gun script. I have been searching all over the internet but have not been able to find any help.

I have the gun working fairly good but when I try to make my bullets change then it does not work properly. My bullet count go down but when I press "r" for reloading then it does not fill up my bullets or lose a clip. if anyone could help I would be most grateful. If any other tips about my script I would also be very happy :)

 public Ray ray;
     public RaycastHit hit;
     public GameObject BulletMark;
     //public GameObject GunEffect;
     public float FireRate;
     public float GunRecoil = 10;
     int Bullets = 8;
     int AmmoLeft = 3;
     public GUIText Ammo;
     public GUIText AmmoClips;
     
     void Update () {
             if(Input.GetMouseButtonDown(0)&& Bullets>0){
                 //Start Shooting
                 InvokeRepeating("Shoot", 0.01f, 1/FireRate);
                 //GunEffect.active = true;
             
                  
 
         }
             if(Input.GetMouseButtonUp(0)){
                 //Stop Shooting
                 CancelInvoke("Shoot");
                 //GunEffect.active = false;
             
         }
     }
     
     
     void Shoot(){
         //Normal Raycast                    //Add a random value to mouse position(r
         ray = Camera.main.ScreenPointToRay(Input.mousePosition+Random.insideUnitSphere*GunRecoil);
         if(Physics.Raycast(ray, out hit, 1000)){
                 //Declear new GameObject variable
                 GameObject BulletHole;
                 //Create the shootmark prefab at the hit point
                 BulletHole = Instantiate (BulletMark, hit.point+(hit.normal*0.001f), transform.rotation) as GameObject;
                 //Rotate the created object at the face of the normal LookAt (hit.point+hit.normal)
                 BulletHole.transform.LookAt(hit.point+hit.normal);
                 BulletHole.transform.parent=hit.transform;
                 
                 hit.transform.gameObject.SendMessage("Hit", 5, SendMessageOptions.DontRequireReceiver);
         }
         
         Bullets = Bullets-1;
         Ammo.text = Bullets.ToString();
         if(Bullets==0){
             //CancelInvoke("Shoot");
         }else{
             if (Input.GetKeyDown("r")&& AmmoLeft>0){
                 Bullets = Bullets+8;
                 AmmoLeft = AmmoLeft-1;
                 InvokeRepeating("Shoot", 0.01f, 1/FireRate);
             }
         }
     }
     
     void OnTriggerEnter (Collider AmmoCrate){
         if(AmmoCrate.gameObject.name=="MoreBullets"){
             Destroy (AmmoCrate.gameObject);
             AmmoLeft = AmmoLeft + 2;
             AmmoClips.text = AmmoLeft.ToString();
         } 
     }
 }