when shooting up/down hill, is the trajectory of the bullet from the axis of the bore the same as when shooting on a level surface?

Nope! Due to the effects of gravity, it drops faster aiming downhill and less uphill.

The flight of the bullet is the same. The moment it leaves the barrel, it starts to arc downward. What changes is your perception of distance and the distance is affecting your bullet.
For example, if a deer is standing at the end of a football field, he is 100yds away. If you were on top of a 100yd tower at the end of the field, you would still be 100yds away as far as gravity is concerned, but if you lasered the buck, he would be 141 yds away. (remember a^2 + b^2=c^2 ?) where a is 100 yds (goal line to goal line) and b is 100yds (height of tower) and c is how far away the buck is from the top of the tower. The only distance that makes any difference to gravity is goal line to goal line. So, if you shoot at the buck as if you were 141 yds away, when in reality as far as bullet drop ie gravity is concerned he is only 100 yds away. If you are zeroed at 100 yds and hold dead on you will hit dead on, but most people think, "wow that buck is 141 yds away, I need to hold a little high" and thus they hold high and shoot high. The reverse is true if the buck is on the top of a 100 yd cliff and you are 100 yds from the base of the cliff.

What usually happens is if you are shooting either downhill or uphill, it "looks" farther and you will hold over to compensate. If you hold over, you will shoot high every time.

Hope this makes some sense. If not, try

http://www.gamecalls.net/huntingtips/upanddownshooting.html

[ 11-29-2003, 10:40: Message edited by: Duckear ]

Actually, the "drop" from the line of the bore will be LESS whether the target is above or below the shooter.(I.e., the shooter would need to hold LOWER on the target) This sounds counter intuitive until one considers a shot straight up or straight down. In the 1st case gravity works to slow down the bullet but does not pull it away from the line of the bore. In the second case gravity would serve to accelerate the bullet but leave it on the line of the bore. For a more in depth discussion:

http://www.exteriorballistics.com/ebexplained/article1.html

As duckear stated the horizonal distance is the determining factor as gravity does not change.A difference in altitude increases the direct distance to the target but does not change the horizontal distance from the shooter to the target.

The question you asked may have elicited the answer you were looking for. In reality, the trajectory of the bullet is different if the muzzle is raised, level or pointed downward. If it is pointed upwards it had an apex to its arc and when level that apex is at the barrel if the barrel is truly horizontal. If downward it will look similar to the level path except that you have introduced a horizontal initial velocity to the path and it will end more abruptly.

As far as shooting and sighting, heed the advice relative to the horizontal distance. The assumption of horizontal distance is an oversimplification as the true drop is slightly different for up and down but for all intent and purposes horizontal distance will do and the difference is academic and minimal.

[ 11-30-2003, 00:22: Message edited by: Customstox ]

thanks for the comments and links. i used the realguns.com external ballistics program and calculated trajectories from 10-50 degrees for my 6.5-284. now i need to incorporate the data into a compact ballistic reference card.