I am making a small project in Unity, and whenever I walk with the gun and shoot at the same time, the bullets seem to curve and shoot off 2-3 CMs from the center. When I stand still this doesn't happen.

This is my main Javascript code:

@script RequireComponent(AudioSource)

var projectile : Rigidbody;
var speed = 500;
var ammo = 30;
var fireRate = 0.1;
private var nextFire = 0.0;

function Update() {
    if(Input.GetButton ("Fire1") && Time.time > nextFire) {
        if(ammo != 0) {
            nextFire = Time.time + fireRate;
            var clone = Instantiate(projectile, transform.position, transform.root.rotation);
            clone.velocity = transform.TransformDirection(Vector3 (0, 0, speed));
            ammo = ammo - 1;
            audio.Play();
        } else {

        }
    }
}

I assume that these two lines need to be tweaked:

var clone = Instantiate(projectile, transform.position, transform.root.rotation);
clone.velocity = transform.TransformDirection(Vector3 (0, 0, speed));

Thanks in advanced, and please remember that I just started Unity, and I might have a difficult time understanding some things. Thanks!