What am I doing wrong with IEnumerator?

I am trying to use IEnumerator to yield between bullet instantiations but it will not yield properly. I got it working perfectly at one point but broke it again later. I think the problem is my misunderstanding of how IEnumerator works.

If anyone knows of a better way for me to achieve my desired function please tell me.

Please have a look over my code and show me what I am doing wrong:

 using UnityEngine;
 using System.Collections;

 public class scarh : MonoBehaviour
 {
     public Rigidbody projectile;
     private bool shooting = false, reloading = false, canShoot = false;
     private int z = 1;
     public int currentAmmo = 20, speed = 500, maxAmmo = 20;
     public float shootDelay = 5.0f;
     
     void Start()
     {
 
     }
     
     void reload()
     {
 //        currentAmmo = maxAmmo;
     }
     
 //    if(currentAmmo <= 0)
 //    {
 //        print ("Reloading!");
 //        reload ();
         //Yield for 3 seconds
 //        yield return new WaitForSeconds(3);
         //Set reload to false so you can shooting again
 //        print ("Reloading complete");
 //        reloading = false;
 //    }
 IEnumerator TimedShooting()
 {
     //While player is shooting
     while(shooting)
     {
         print ("Running IEnumerator");
         //If there is a projectile
         if(projectile)
         {                
             //Instantiate projectile
             Rigidbody newProjectile = Instantiate(projectile, transform.position,
                                                               transform.rotation) as Rigidbody;
                 
             //Give projectile velocity
             newProjectile.velocity = transform.TransformDirection(new Vector3 (0, 0, speed));
                 
             //Remove 1 from currentAmmo
             currentAmmo -= 1;
                 
             //Yield before next shot?
             yield return new WaitForSeconds(shootDelay);
                 print ("Yielding");
         }
     }
 }
     
     void Update ()
     {
         //When holding down Fire1
         if (Input.GetButton("Fire1"))
         {
             shooting = true;
             StartCoroutine ("TimedShooting");
             print ("Shooting: " + shooting);
         }
             
         //When Fire1 is released
         if(Input.GetButtonUp ("Fire1"))
         {
             shooting = false;
             //Set shooting to false
             print ("Shooting: " + shooting);
         }
             
         //Switch fire mode when Z is pressed
         if (Input.GetKeyDown(KeyCode.Z))
         {
             z = (z % 3) + 1;
             print (z);
         }
     }
 }