Everything that is able to shoot on a Battletank can make it much less effective in Battle.
Even .556 or .545 can bring up trouble.
Its not that everytime the whole Battletank has to be blown up.
If you are part of the crew of the damaged Battletank you see yourself encountered with much more Workload in the first place, which can turn your Battletank into a big Burning Coffin pretty fast.
In my personal opinion in RL the GAU-8 is a very effective tool against Battletanks as well as the GAU-22.
ISE
Ex Leopard 2A5 TC