Now for the bullet-

A bullet fired from gun (when the barrel is perfectly level) over tranquil ocean (for the purposes of creating the most perfect earthbound surface) will likely strike the surface of the water at exactly the same time as the bullet dropped from exactly the same height at the exact same time the other bullet was fired [huh?]. The lateral velocity of the bullet will not have any effect on or resistance to gravity, the bullet simply isn't that fast.

Now, I said "likely" not because I was unsure, but because the two bullets will encounter different conditions. The fired bullet will travel through more air than the dropped bullet and may encounter an updraft or downdraft. Were it possible to conduct this experiment in a perfect vacuum, the two bullets would strike the surface at exactly the same time, every time.

::edit to reply to Rinky::

Just because the conveyor is turning does not mean that the plane is not moving.

::ETA:: In fact if the conveyor is moving at all, it is because the plane is moving forward. The scenario calls to match the plane's speed, not its power or friction or any other imaginable thing.