Im making a mulitplayer shooter and when i shoot it fires out of the barrel using the spawnpoint i made but then it shoots really fast out of another location please help!

EDIT!!!! i tried changing the code to getbuttondown but it still fires out of the barrel plus the mag!

This is my code:

var projectile : Rigidbody;

var speed = 20;

function Update () {

if ( Input.GetButton ("Fire1")) {

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

Destroy (clone.gameObject, 2);

}}