Bullets firing Bullets?

I've been trying to get some bullets to instantiate at the barrelEnd position and move forwards towards the player, but it's turned up interesting results. Basically, when i fire a bullet, it moves forwards but then instantiates a new bullet on the bullet i just fired as it travels towards the player. This means that one bullet becomes two,then two bullets become four and it keeps increasing exponentially. This causes a lot of lag and has pretty much stopped my progress. After experimenting with some different ideas, I ended up with a bullet that fired guns, a gun that fired it's barrel and bullets that sit still in the barrel but don't increase exponentially.

I know that the problem is caused because bullets are instantiating on bullets, so that means they'll even spawn on clones of bullets. Those print commands were for debugging stuff, so yea.

 #pragma strict
 
 public var PistolBullet : Rigidbody;
 public var barrelEnd : Transform;
 
 
 function Update ()
 {
     
     if(Input.GetKeyDown(KeyCode.Space))
     {
     
         print ("bbbb");
         var BulletInstance : Rigidbody;
         print ("vvvv");
         BulletInstance = Instantiate(PistolBullet, barrelEnd.position, barrelEnd.rotation);
         print ("Debug thingy");
     }
 }
 
 
 function OnCollisionEnter (col : Collision)
 {
     if(col.gameObject.name == "Bullet Time Chamber 01")
     {
         Destroy(col.gameObject);
     }
 }