Not a mechanical engineer or a physicist, but your statement would only be true in controlled conditions.
Depending on the round, for example, they can tend to gain some altitude as they fly, and as the velocity slows they drop. The air has a lot of effect.
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Actually the air has little or no effect except to slow down the round or blow it off target. Because barrels are riffled the bullet spins. Any aerodynamic advantage from the shape of the round will be averaged out to zero. There are situations where the bullet could be tilted and “ride” the air up but that would be very rare indeed, or, come from elevating the barrel in the first place. I am only talking about a level barrel.
The purpose of aiming high on a distant target is not overcome the air resistance but it is to overcome gravity.
I realize this all sounds counter-intuitive but it is true.
Not going to argue gravity...It’s a constant.
But a bullet that can swerve off target as you correctly stated, can also swerve up or down.
It can also tumble. It’s been a while for me but if you look at the ballistics of some rounds, mostly in the rifle category. You will see a round that leaves the barrel on a trajectory that sometimes rises before it falls. Depending on the rifle and the bullet characteristics in flight.
It just is what it is.
Anytime you use the “dropped” mass association to a fired bullet trajectory, you have to do it in a vacuum so you take the medium that the object travels through out of the equation.
It’s a rather anal point, but it’s valid and that is all I was saying.. In the end, with gravity, everything falls at the same rate, but the air or whatever medium you choose, has a input on that rate and on the velocity.
A good analogy is a BB gun. Not all BB’s are round enough to be consistent. Some fly differently...up/down and sideways.
I see that everyday when I am harassing my resident squirrels who enjoy the game of “empty the bird feeder”.