"Someone once told me that a 30.06 rises above the line of sight in the first 100 yards, then begins to drop off after that.
Is there any truth to that statement, does anyone know ????"
Simple answer, yes, but technically, no.
Bullets tend to rise above the LOS (line of sight) becuase they are usually fired at a slight up angle. No bullet has a lift factor that will make it gain elevation in the flight path. In fact, if you were to hold a barrel perfectly level and you were to drop a bullet from the same exact hight of the barrel at the same time you fired, they would both hit the ground at the same time provided the ground was perfectly flat.
The slight arc is done to increase the range in which your rifle is "zeroed." (The following numbers are used purly for discussion) If your bore were to be level the shot would start with a flight path 1.5 inches below the LOS. Since all bullets immediatly start to drop, the distance between the bore and LOS would gradually increase and you would have to hold over your target every time. Example, 1.5 in @ muzzle, 3 in @ 100 yds, 8 in @ 200 yds, 24 in @ 300 yds and so forth.
Since the bullet starts the drop immediatly, if you shoot at a slight up angle your bullet will beable to travel slightly further before hitting the ground. Think of a footbal or artillary round.
Besides the benefit of longer distance, when shooting game animals, you do not need to be as precise as shooting for competition. Usually the ability to place a bullet in a 6 inch circle at any given range is good enough. Because of this, your bullet can travel a bit above and below the LOS and allow you to take game. If the bullet starts 1.5 in @ the muzzle and you shoot it at a slight up angle it will cross the LOS at say 25 yds the be 1.5 in high @ 100 yds, 3 in high @ 200 yds , back down to 1.5 in high @ 300 yds , cross the LOS again at 375 yds, and be 4 in low at 450 yds.
As you can see, the distance at with you can keep your bullet in that same 6 inch circle, at least elevation wise, circle is greatly increased if you shoot it upwards instead of perfectly flat. This is also known as Point-Blank Range.
I hope this clears it up some.