With the PB4Y you should use naval mines instead of the 2000 lb bombs. You can drop three and destroy a base with them because they have more explosive filler than regular 1000lb bombs.
When youre bombing in realistic, do you drop when the center of your crosshair is on the base, or do you drop when the small transparent circle just below the crosshair is on the base?
You drop with your crosshair on or a little earlier than the base, the transparent circle (it displays your angle of attack) should be at 0°, this will improve your bombing accuracy even more
