My impression is that currently the flak is far to imprecise and most of the times miles off. Anyhow very ineffective imho. It currently seems just to be spay and pray as if the gunners even did not try to do some aiming and following of the enemy plane. They just carpet (in a very spread manner) the area somewhere around the plane but not really aimed. Absolutely no danger.
I think it should be a good deal better. I would like to have the thrill of flak when closing in on an enemy airbase or an important and heavily defended target.
Not good quality but at least some images from the time period of BOB.
An interesting (and quite dramatic) clip from the battle of Okinawa. It is for sure lot later in the war than Bob but it shows quite nice the AA of a battle ship.