Bullet drop depends on several thing's and not one thing. Of course the most obviously velocity does effect it. Actually velocity effect's time of flight. Equal bullet's started at different velocity will show different drop because of time of flight. Barrel length will effect drop for no other reason than equal loads fire in two different rifles with different barrel lengths will give less drop to the longer barrel for no other reason than time of flight is longer for the longer barrel. Bullet shape will also effect drop. A round nose bullet is ballistically inferior to an equal weight spitzer type bullet. Even if started at the same velocity, the spitzer will cut the air a lot better and maintain a velocity advantage once they are fired, time of flight is effected. The way you sight in your rifle will also effect bullet drop. ie: sight in the rifle at 100 yds dead on and then take the same rifle and load and re-sight at some farther distance. The time of flight doesn't really change other than the trajectory you've given the same bullet. Your 30-06 with a 180gr bullet sighted in dead on at 100 yds will hit the ground sooner than the same exact load from the same rifle but sighted in at a longer distance. For every rifle there is a sweet spot and that is determined by the size of the trget your shooting at. If you sight in to hit a 4" target and never have the bullet go more than 2" high or 2" low all the way to the target, time of flight will be effected for no other reason than the trajectory you chose. Take the same load and the same rifle and sight it in for an 8" target and the same rifle/load will hit the bigger target farther away. The bullet with the 8" target takes the bullet farther without ever leaving the 8" circle by 4" high and 4" low, that is 4" above and below the line of sight. Changing the sight in to take advantage of what you want from your rifle and what it has to give you will, because of trajectory, change time of flight.
Take a 180gr bullet and drop it in front of the barrel and it will hit the ground at the same time s the same bullet actually fired from the rifle perfectly level to the ground. The distance each falls will be exactly the same but without trajectory made with sight alignment, nothing changes. When a bullet leave's the barrel, any bullet, it immediately start's to fall. It rise's above line of sight because of the trajectory you give it by sighting it in at some particular range.
