point of impact change when shooting up or down hill

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ncnbrsa

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Can anyone give me information on how to determine bullet impact point when shooting at varying degrees up or down?
An example would be that you have a zero at 100 yds and now you are shooting a hundred yards out but 30 degrees down hill.
The rifle is a 243 with 100 grain bullet and 33grains of Hodgden 4895 traveling at 2700 fps.
 
As far as I know you have to figure it using basic trig.

Uphill or downhill the holdunder is exactly the same, you hold for the horizontal distance.

The easiest way to illustrate it is to use "Ye Olde Bowhunters Trick"....... when shooting downhill in trees, like on a hillside or more usefully p'raps when shooting from a treestand, you pick the tall tree closest to your quarry and estimate or laser the LEVEL distance to the tree trunk. Shoot for the level distance.

This is not an approximation, actual mathematical hold is the LEVEL distance above or below your target.

Sniper Tools is the one I've been mounting. It's light and fairly stout. Buy the milspec version.

( http://www.snipertools.com/article.htm )

Some long range shooters like Darrell Holland still hold that the BEST way is to carry a Suunto clinometer around your neck.

( http://www.suunto.com/en/Products/Precision_instruments/Suunto--PM-5/ )

Leupold sells a ranging clinometer/binocular that from all reports works as advertised.

When using a scope mounted Sniper Tools unit note that the ACI version (Angle Cosine Indicator) and the ADI version (Angle Degree Indicator) are identical except for lettering. You use the one you're most comfortable figgering, one is the 'reverse' of the other.

For the math-challenged like I'm (spell that L.A.Z.Y.) I just pick a number in the middle and Kaintucky it from there......

You do NOT have to figure for trajectory, figure for poi and let 'er fly.... it don't matter if it's a 50cal flintlock nor a 50BMG.

hth


al
 
Remember that there is a difference between ballistics and hunting.

Ballistics is easier. For hunting, if you're looking up -- or down -- at that deer, where their internals are (heart, lungs) "changes" based on the 2-dimensional picture you see. So if you're shooting uphill and put the crosshair just below the elbow, you're apt miss the vitals -- regardless of ballistics, you have to hold lower. If shooting downhill, it's the opposite. Just think 3D and you're OK. Paper targets are 2D, so they're all ballistics.
 
trajectory

ncnbrsa said:
Can anyone give me information on how to determine bullet impact point when shooting at varying degrees up or down?
An example would be that you have a zero at 100 yds and now you are shooting a hundred yards out but 30 degrees down hill.
The rifle is a 243 with 100 grain bullet and 33grains of Hodgden 4895 traveling at 2700 fps.
Click to expand...

I believe your effective range would be 87 yds and the path of your bullet would only be .1" over your line of sight at the range. In this example you could hold dead on. nhk

http://www.mathsisfun.com/sine-cosine-tangent.html
Mildot Master http://www.mildot.com
 
There is an interesting article on this subject in the June 2010 issue of 2010 (page 60). It points out that there is considerable variation among authoritative sources about how to compensate for steep shots. It is part one. Evidently, the plan is to do some actual testing, and report the results in part two. I found the discussion illuminating, particularly as to the proper use of an angel cosine indicator, and will be interested in the how the results that are to be reported conform to the various methods of computing correction for uphill or downhill shots.
 
Article

Boyd Allen said:
There is an interesting article on this subject in the June 2010 issue of 2010 (page 60).
Click to expand...

I read the article (again) and that got me curious so I pulled up a trajectory table for my .308 and set it at a 100 zero and then printed out a trajectory graph and a drop graph and superimposed them with the same starting point and found the the two curves don't converge until about 425 yards and there is a difference at 350 yards that could account for being ~6 inches over. I assume that the line of sight is used for range correction, but in the case of my .308 that wouldn't take into account a 1.8" difference at the muzzle and a 100 yd zero. Since the wind is blowing and it's cold out I'm a keyboard shooter today :) - nhk
 
As I read this thread I just thought of a method that might work. Remember this is just something I haven't given a lot of thought to so I may be all wet.

Consider the angle you are shooting at could vary between zero and 90 deg. Now you know at 90 you will have zero drop. Then lets say you know that at 0 deg you have say 10" drop. Just multiply the drop by the proportion of the angle left between angle you're shooting at and 90 deg. For example, if you want to shoot at a 30 deg angle then that is 2/3 away from 90 so just multiple 10" by 2/3 and you have about 7" for a drop at 30 deg. If you wanted to try 45 deg then you would be half way away from 90 so your drop would only be 1/2 X 10" or 5". At 60 deg you would only be 1/3 away from 90 so you would only drop 1/3 X 10" or about 3". Try it, it's easy to do in you head and maybe it works, I haven't time to write the simple equation, or see how it might agree with the science.
 
I appreciate all the responses to the post I made. It gives me a lot to digest. The post made are much more than what I expected.
Thank you all
Ron
 
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