This cant be realistic - 500+ hits, plane still flying??

Best way to take out 111's is to fire at your convergence and aim for the engines or the wing roots inboard of the engine. Loaded with cordite and De wylde rounds in each gun it often doesnt take much to blow a wing off when the fuel tank explodes. Though admittedly this doesnt always work, the best thing to do is fly as a group and pick one out to take down. This way you can kill 3-4 before everyone is out of ammo.