first person shooter help

I'm making a first person shooter and using the tutorial but I'm having trouble with shooting. I made a sphere called missile and it's good - it blows up when it comes in contact with anything. But I can only shoot them up till the original blows up and I want to be able to shoot forever so please tell me how I can make it so I can shoot forever.

var projectile : Rigidbody; var speed = 20;
function Update() {
    if( Input.GetButtonDown( "Fire1" ) ) {
        var instantiatedProjectile : Rigidbody = Instantiate( projectile, transform.position, transform.rotation );
        instantiatedProjectile.velocity = transform.TransformDirection( Vector3( 0, 0, speed ) );
    Physics.IgnoreCollision( instantiatedProjectile. collider, transform.root.collider ); 
    }
}

well i think that when you press fire1 it fires one time if you want really fast firing you can change `Input.GetButtonDown("fire1")` to `Input.GetButton("fire1")` and this will make it shoot really fast.

but if you wanted to make a controlled firing you could do somthing like this

var projectile : Rigidbody; 
var speed = 20;
var fireRate : float = .1;
private var nextFire : float;

    function Update() {
         if( Input.GetButton( "Fire1" ) &&Time.time>nextFire) {

                nextFire = Time.time+fireRate;
                var instantiatedProjectile : Rigidbody = Instantiate( projectile, transform.position, transform.rotation );
                instantiatedProjectile.velocity = transform.TransformDirection( Vector3( 0, 0, speed ) );
            Physics.IgnoreCollision( instantiatedProjectile. collider, transform.root.collider ); 
            }
        }

the var fireRate = the time between each fire so for a machine gun it should be about 0.06;