As I said earlier on, forget all the bombings you used to do. Level bombing does not not pass over a target at 300mph, drop 3 bombs, turn on a dime, drop 3 more. Bomb runs are required.
A bomb run begins at about 6~8 miles prior to target. The desired altitude is between 10k~18k, any lower than that you are cannon fodder, any higher and don't expect any sort of 'good accuracy'. When a bomb run starts, you will approach at the target in a straight line at a stable speed. Accelerations or deccelerations will kill off whatever calibration you've attempted - and this is the reason why a bomb run requires at least 6~8 miles. Starting a bomb run closer than that will not give you enough time to calibrate the sights. (If your airspeed is too high, you will inevitably throttle down to buy enough time to calibrate. The buff will be slowing down as you calibrate, and thus, the speed when you drop the bombs will not be the same as the speed you calibrated the sights).
Set up a straight flight path, and set to about 75~80% maximum throttle.