Gun shooting sideways. NEED HELP!!!

Okay Im starting on making a FPS game and I have a code for shooting animation, and when I test it I shoot forward but when i look around I sometimes shoot on a weird angle and if I look back its fine again. NEED HELP!!

Here is my code

 var bullet : Rigidbody; //Your bullet prefab. Should have a RigidBody
 var speed : float = 100.0f;
 var muzzlePoint : Transform; //Your SpawnPoint
 
 function Update() {
     if(Input.GetButtonDown("Fire1")) {
         var instance : Rigidbody = Instantiate(bullet, muzzlePoint.position, 
                                                muzzlePoint.rotation);
         instance.velocity = muzzlePoint.forward * speed;
     }
 }