[jdkelly]

This is a follow up question to the previous question entitled "Physic 101 of bullet and gravity".

You've taken your new bench rest rifle, chambered for the new "SuperFastFlatShootMagnum" mounted the expensive HubblePerfectOpticSuperLongeRange scope, out to rifle range and sighted the rifle to hit point of aim (line of sight) at 1000 yards.

As you sit on the bench you notice that a trophy Whitetail is standing 1000 yards away from you at minus 45 degrees from the horizontal (below you) and a trophy Mule deer is standing 1000 yards away from you at plus 45 degrees from the horizontal (above you). Assuming no outside interference from the elements such as wind, rising air currents and the like. Although the "SuperFastFlatShootMagnum" is the flattest shooting round made by man it still has to fly in an arch above the line of sight to hit the point of aim.


1) Where would you hold the point of aim on the Whitetail relative to the same point of aim if the animal were 1000 yards from you on the horizontal?

a) Above the intended point of impact on the Whitetail
b) On the intended point of impact on Whitetail
c) Below the intended point of impact on Whitetail

2) Where would you hold the point of aim on the Mule deer relative to the same point of aim if the animal were 1000 yards from you on the horizontal?

a) Above the intended point of impact on Mule deer
b) On the intended point of impact on Mule deer
c) Below the intended point of impact on Mule deer

Extra Credit: Why?



jdkelly

[TarpleyG]

This is where a good mil-dot scope and the knowledge to use it comes into play. This is something I have started to get into but I cannot answer the questions without some research. By then, both animals would be long gone. Be interesting to see the forthcoming answers.

GT

[Navy joe]

c for both. Probably very close to the same point of aim for both up & down. Gravity has the greatest effect on a bullet's drop when the bullet is traveling perpindicular to gravity's vector(straight down)

1. What's this gotta do w/ handguns?

2. What kinda hills you got out there anyways?

[Mal H]

Joe's right. C in both situations.

http://www.thefiringline.com/forums/showthread.php?s=&postid=1008515#post1008515

[bountyhunter]

For the "flat" horizontal sight in to POA at 1000 yards, the scope is set so that the bore of the gun is aimed upward exactly enough to make the bullet rise the the sum total of: the linear distance between the barrel's bore axis center and the scope sight line PLUS the linear distance of downward fall due to gravity over the 1000 yard flight.

Rotating the gun upward (or downward) reduces the amount of distance gravity will cause the bullet to move in a direction vector at a right angle to the bore. Hence, the gun will hit high as it is rotated up or down as the effect of gravity on the flight is reduced. So, you would need to aim lower to hit point of aim.

[euclid]

It's not going to matter. Use the same POA that you would use if the deer was dead level in front of you. The acceleration due to gravity dimishishes with the square of the distance (i.e. r^2) from the center of mass (i.e. the center of the earth). Since 1000 yards is so small relative to the distance to the center of the earth (i.e. center of gravity= center of mass) the effect will be negligable. The only scenerio in which the above would not be true is when the deer is hovering directly above or below you...the effect of gravity would pull it straight down toward the center of mass in a linear fashion, all other things being equal. Every other possible trajectory would be parabolic.

cheers

[Handy]

I already posted on this in 101:

The slippery application of all this is when shooting a rifle up or down slope. In either case, the holdover is less, for a given range, than a horizontal shot. Is the bullet dropping less? NO! It's just that the shooter is viewing that vertical drop from an angle, which makes it appear shorter (distended), since the reticle is no longer parallel to the vertical drop.

[bountyhunter]

Handy is correct. It's a slightly different way of saying what I did:

"Rotating the gun upward (or downward) reduces the amount of distance gravity will cause the bullet to move in a direction vector at a right angle to the bore. Hence, the gun will hit high as it is rotated up or down as the effect of gravity on the flight is reduced. So, you would need to aim lower to hit point of aim."

The key phrase is it reduces the amount the bullet falls due to gravity IN THE DIRECTION OF A RIGHT ANGLE TO THE RIFLE BORE. The bullet is still in the air the same amount of time and still drops downward toward the center of the earth the same distance, but that direction of fall is at a 45 degrees incline to the bore axis.

The gun is sighted in assuming the FULL distance of gravith drop straight down as the shooter looks down the gun. Aiming 45 degrees up or down, the bullet's gravity motion direction would be at a 45 degree angle towards or away from the shooter (depending on shooting uphill or down) reducing the amount of "gravity drop distance" that the scope-in needs to correct for. Ergo, too much gravity drop correction would have been dialed in if set for "level", so the gun would be aimed too high when shooting at an angle (regardless of whether you were shooting uphill or downhill).