instantiate works on one but not other object

Hello all!

I'll try to be brief. I have a turret, consisting of a cockpit (with a "fire control" script on it), and two barrels with "Shooter" objects. When the turret sees a target, fire control will send a "fire" message to each shooter, firing a bullet. Relevant part of firing script :

             var fireShot : FireShot = turret.GetComponent(FireShot);
             projectileSpeed = fireShot.shotSpeed;
             fireShot.fire();
             Debug.Log("Fire a bullet?");

Now, here is the actual firing script in the shooter :

 var ammo : GameObject;
 var strength : int = 10;
 var shotSpeed : float;
 shotSpeed = strength * 10;
 
 function fire(){
 fwd = transform.forward;
 shot = Instantiate(ammo, transform.position , transform.rotation);
 Debug.Log("Just'made' a shot");
 shot.rigidbody.AddForce(fwd * 500 * strength);
 }

My issue is I have a new bullet type that doesn't work. I had used cube shaped bullets with a rigidbody and a few scripts on it, collider, etc. I also made a second, newer "bullet" which was a plane with a bullet texture, with the same scripts and rigidbody, and a sphere collider instead of a mesh one.

I wanted to change out the "ammo" objects on my turrets, and here were the results :

If BOTH shooters are firing cubes, they both fire. If one shooter is firing cubes and one is firing plane bullets, they both fire. If both shooters are firing plane bullets, they do not fire.

Please help!

Cheers, Marcin