What did I wrong with my gun script???

I maded a Gun script but all my bullets don't hit somthing they just fly through everything. Can someone help me??

Here's the script:

var projectile : Rigidbody;

var speed = 20;

var shootsound : AudioClip; var shootanimation : AnimationClip;

function Update(){

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

animation.Play("m4a1-shoot");
audio.PlayOneShot(shootsound); var instantiatedProjectile : Rigidbody = Instantiate( projectile, transform.position, transform.rotation );

  instantiatedProjectile.velocity =    transform.TransformDirection( Vector3(

0, 0, speed ) );

     } }