I believe "hold fire" instructs the gunner to stop firing.
I don't want him to stop firing altogether.
I would like him to find another target and stop firing countless rounds into the ground or building etc., which is preventing him from hitting his current target.
Instead, I would like him to find a new target that he "can" hit.
I've tried finding another target for him but he keeps shooting at the initial one.
I've tried telling him to scan in another direction, which he does then locks back on his original.
By this time I'm usually dead from all the other enemy coming at me.
I've even tried using reload, but then it's back to the same target.
Only thing that sometimes works is to retreat completely out of sight then move forward again.
(By this time my tank has usually expended most or all of it's ammunition)
Only other thing that works is if someone else happens to destroy the target for me.