Here is a pretty good short read on bullet trajectory, especially the last one on drop, that may be of help to some regarding this thread:

To understand what happens from muzzle to target and why–or at least to the extent we hunters need to know–here are some definitions and fundamental concepts one must be familiar with before all the pieces can fall into place.
DEFINITIONS
Line of Sight (LOS): A straight line out to infinity as represented by the scope’s reticle, or the sighting plane formed when the front and rear sights are aligned.

Line of Departure (LOD): Another perfectly straight line, this one running down the center of the bore to infinity.

Bullet Path: The arc or trajectory of the bullet relative to LOS.

Drop: The actual drop of the bullet relative to LOD. I’m sure we’ve all heard someone describe a rifle as being so flat-shooting “the bullet doesn’t even drop for the first 100 yards!” Nonsense. Even with the flattest-shooting super magnum, the bullet starts dropping away from the LOD the moment it leaves the muzzle. A popular misconception is one that results from the use of the word “rises” in various ballistics charts. A bullet is always dropping, but it does indeed “rise” relative to the LOS. This seeming anomaly exists because with the scope being positioned above the bore, the only way the LOS could converge with the bullet path is to angle the sights downward. In other words, if the LOD and LOS were parallel, the bullet would exit the muzzle 11⁄2 inches low and start falling farther away from there.

Adding to the confusion is the fact that, once those sights are angled downward to converge with the bullet path at some practical distance downrange–whether it be 100, 200 or 300 yards–the bullet and LOS will have already converged once before. Whether we’re shooting a .45-70 that we want zeroed at 100 yards or a 7mm Ultra Mag at 300, this first convergence of LOS and bullet path occurs between 20 to 40 yards from the muzzle.

Read more in this link if you like and look at the graph at the top showing the terms and how they relate in the description: http://www.rifleshootermag.com/2010/...#ixzz2EwxDYFkS