Altitude Correction For Steep Shooting Angles

[Tumbleweed]

Hi guys. The kids and I went out scouting last night and found a couple of bulls out feeding in a grassy slide at 900 yards. I got to thinking about the conditions and planning the shot (if it was elk rifle season) and began to think about the shooting angle along with the change in altitude that the bullet would experience crossing the canyon. My Kestrel showed 2,050 feet at our shooting position, my phone using "shooter" measured the downhill shooting angle at -13 degrees. Tonight I looked on Google earth for the altitude at the elk's position and it was 1,050 feet.
So, the question: how do you calculate the correct altitude for and shot like this where the altitude will change 1000ft or much more between shooter and target? If using absolute pressure you won't know what the pressure is at the target either. My guess would be that one would take the shooter's altitude and target's altitude (if known) and split the difference? In the case of the elk we were watching, would the shot altitude be 1,550ft?

A question on the "Shooter" program:
In the example of this elk scenario I put my info into shooter including my altitude and -13 degree look angle. Is "shooter" smart enough to use that -13 degree look angle input and altitude at shooter's position input to figure out the altitude or pressure at the target? If so does it come up with a more accurate "average" altitude that goes into the solution? Thanks!

 

[bigngreen]

I would contact the developer and see if Shooter take the elevation change into account, I suspect it does. I know both Applied Ballistics and Patagonia Ballistics take the air density change into account based on shot angle.

 

[MMERSS]

Good question. On the other side of the coin anything less than 600 feet or so of elevation change I'm not too concerned about. In your example using similar weather conditions where I usually hunt and a 650 foot elevation change with a range of 900 yards I show a ballistics solution difference of approximately 1 inch.

 

[Alan Griffith]

You can see how much of absolute pressure changes here.

Air Pressure and Altitude above Sea Level

....1.1 in/Hg. Play with that number in your ballistic app and decide for yourself if it's of concern to you. For me, it's .6 moa or two clicks. Might just split the difference and click up/down 1/4 moa and shoot at or near the actual conditions you might encounter.

Alan

 

[Tumbleweed]

Thanks for the responses guys. I will study this some more. It may not create much of a change in POI but I want to be as precise as possible on that first shot.