From Bob Spencer's page:
Many hunters, for whatever reason, sight their rifles in for too short a range. By doing so, they lose much of the potential of the gun and make the job of hitting accurately with it over a variety of ranges very difficult. To illustrate this, we'll look at two trajectory charts generated by Gun Controller®, by RSI. Because I'm strictly a roundball shooter, they will illustrate roundball trajectories, but everything we will discuss is exactly the same for conicals. The charts show the trajectory for a .530 inch lead ball of 223.5 grains weight, fired at a velocity of 1800 fps. All parameters for the two charts are exactly the same except for the distance at which the rifle is sighted in. First, consider what we get if we sight the rifle in for 50 yards. On the plot, the line-of-sight is shown as a straight black line at the top, marked with a "0" , and the path of the ball is shown in red. Drop is the curved blue line, but that's of no concern to us now.
It is easily seen that the path of the bullet deviates very little from the line of the sights out to 50 yards, rising to only 0.13 inches above it (Mid-Range Trajectory) at 38 yards. Notice, though, that at 100 yards the ball is 3.77 inches low, and at 125 yards it is 8.15 inches low. A definition must be discussed here, that of Point Blank Range. Technically, it is the range at which the ball falls as far below the line of sight as it had risen above it at the Mid-Range Trajectory. Practically, it means something more useful to us, and that is the range at which we can pretend the rifle is doing just exactly what we would like it to do, shoot in a perfectly straight line. Point Blank Range is given as 56 yards in this chart, and that means that for any target from the muzzle out to 56 yards we can just point and shoot, and we will hit. Out at 125 yards, though, where the ball shoots 8.15 inches low with the rifle sighted for 50 yards, it will require some good guessing to put the ball where we want it.
Now, let us consider the situation if we sight the rifle in for 100 yards, not 50 yards.
Of course, your ball could be traveling at 1800 fps with 95 gr of Ffg, or it could be much less....