Elevation Impact on Zero?

Discussion in 'Hunting' started by Bobson, Sep 6, 2020.

  1. Bobson

    Bobson Member

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    Good morning.

    I’m hunting antelope in Wyoming early next month. Elevation is about 6200’. Where I live currently, elevation is about 600’.

    How much of a difference is that ~5600’ going to have on the zero of my rifle? I understand that it’s going to vary based on other factors too (temp, humidity, load, etc), but I‘m thinking this is the factor that I might be able to most-accurately account for. If I can adjust the zero my rifle here and just take one shot to confirm after arriving, that may be a lot easier than having to completely zero my rifle there.

    Those are my thoughts, at least. Please correct me if I’m wrong. This is my first out of state hunt. I attended a Wyo hunt a couple years ago, but I was basically just a spectator.

    Thanks for the help.
     
  2. Cemetery21

    Cemetery21 Member

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    Just plug data into a ballistic calculator such as https://www.hornady.com/team-hornady/ballistic-calculators/#!/4dof
    I just entered a 135 gr 6.5 @ 3,000 fps and got .38" difference at 300 yards. So, if that holds true, a little over 1/4" higher hit at the higher elevation.
    Good luck holding less than 1/2" at 300 in field conditions, even if your rifle is capable.
     
    Last edited: Sep 6, 2020
  3. WrongHanded
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    WrongHanded Contributing Member

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    I'm not going to pretend that I know to very much about the finer details of how air density effects ballistics. However, it's my understanding that temperature and humidity have a much greater effect on air density than elevation. Cold and humid mountain air is certainly dense compared to the dry arid heat of low lying deserts.

    I'd give serious consideration to checking/adjusting zero when you get there. That way you know for sure.
     
  4. Bobson

    Bobson Member

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  5. Bobson

    Bobson Member

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    I hadn’t considered the effect of temp/humidity on the air’s density. I had heard they play a role but had never given thought to why. I’ll definitely make it a point to confirm my zero up there, and adjust as needed. Thank you.
     
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  6. WrongHanded
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    WrongHanded Contributing Member

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    I think more important than a POI shift due to temperature, humidity, and elevation, wind drift is going to be your concern in much of Wyoming. There's always some (frequently quite a lot) out on the plains. If you spend time on a ballistic calculator, that might be a better place to focus your efforts.
     
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  7. buck460XVR

    buck460XVR Member

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    ^^^I agree......and YOUR elevation as compared to the animal's elevation(uphill/downhill) will have more influence than that of the general elevation. I myself wouldn't worry about adjusting for the overall elevation.
     
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  8. Laphroaig

    Laphroaig Member

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    Its always a good idea to check your zero at your hunting location if possible.
     
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  9. horsey300

    horsey300 Member

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    You'll have to re dope, the wind and downrange performance will differ more that just the 5600' zero change. Coming from a more humid lower elevation to a drier, windy climate will be different enough to re dope at several distances, your drop will be less extreme but that drift will getcha!
     
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  10. H&Hhunter

    H&Hhunter Moderator Staff Member

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    Running the numbers at 500 yards an identical load will have about 1” less drop at 500 yards at the higher elevation. AKA not enough difference to worry about.
     
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  11. H&Hhunter

    H&Hhunter Moderator Staff Member

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    True and many hunters still believe the old fairy tale about “aim high uphill, aim low downhill”. That is a total fallacy, the angle is what matters whether it’s up or down. The hold is the same for angle corrected range.
     
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  12. daniel craig

    daniel craig Member

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    Re-zero when you get there and the rest is irrelevant.
     
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  13. mokin

    mokin Member

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    I agree with those who mention the wind. That will probably be the biggest concern.
     
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  14. FL-NC

    FL-NC Member

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    That is quite the can of worms. Elevation does effect ballistics. This is of course magnified as range increases. In afg. at 8,000 feet, our ballistics on our M24's and SR25's in the winter were very effected compared to our data collected at Ft Bragg (basically sea level) in the fall. Ballistic calculators (we used Horus ATRAG) and Kestrels were essential for what we were doing. Make sure to bring enough ammo to do a good zero on arrival- not just due to changes in environmental conditions, also for and bumps and bruises your gun experiences during travel. Wind is also a serious consideration, and Wyoming can be pretty windy.
     
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  15. Bobson

    Bobson Member

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    We’ll both be using angle-compensating rangefinders to get our range, so we’ll be sure to adjust for the correct angle-compensated range prior to taking our shots. My brother has a couple tags and I just have the one. We did hunt antelope together a couple years ago in the same GMU (I was along for the company and he lived there at the time), and we were able to stalk to within <100 yards of the herd several different times.

    As for the wind, I’m using a ballistic calculator using my exact load, and recording numbers for different values and wind speeds. I’m not sure how else to mimic wind conditions to record DOPE. It just doesn’t get nearly as windy here.

    I’ll definitely confirm my zero after arriving, and adjust it as necessary. Bringing plenty of ammo for it.

    I appreciate all the feedback.
     
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  16. JJFitch

    JJFitch Member

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    I get the jest of your question. You didn't mention the firearm or cartridge you will be using. Ballistic coefficient of the bullet will affect bullet drop.
    But: As mentioned above wind may be a bigger factor.
    : Variations in ammo may be a bigger factor
    : Shooter ability may be a bigger factor

    40 + years ago shooting "goats" in eastern WY my win. .243, 100 grain, Sierra Spitzer did the job from 40-200 yards. I didn't know anything about compensation at the time! But then again the "243" has a reputation of being a "flat shooter"!

    All the best,
     
  17. H&Hhunter

    H&Hhunter Moderator Staff Member

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    Just because it’s fun I’ll throw this out there.

    A bullet is affected by air density in a nut shell the less dense the air the less drag and flatter a given bullet is going to fly.
    Higher altitude and warmer temperatures equals less dense air, bullets will drop less at range.

    lower altitude and colder air equals more dense air and bullets will drop more at a given range.

    The factor you are looking for is a density altitude calculation. Density altitude is actual altitude above MSL (Mean Sea Level), so the actual altitude in feet above average sea level, that is corrected for atmospheric pressure and ambient temperature. That calculation will give you the local density altitude at your location for the temperature. Density altitude is a measurement of the density of the air and that defines how much drag your bullet encounters during flight.

    As an example on a standard pressure day with the atmospheric pressure being 29.92” or 1013MB for you metric users. The density altitude on a 95 deg F day (35c) at my house which is 6500’ above sea level (MSL) is roughly 10,000 feet. So a bullet is going to fly like it was shot at 10,000’ which means it has less air density that creates less drag and the bullet will decelerate at a slower rate, therefore having less drop for a given range.

    Conversely if we go to Caribou’s home in the Arctic in the winter and shoot the same bullet at sea level during a day that is -10 deg F (-23c) the density altitude that the bullet now has to contend with is negative 4500 feet below sea level. The air is far denser than than the previous example and the bullet will decelerate much faster so it will have more drop at a given range.

    However at more reasonable temperatures and within reasonable altitudes the difference In drop are not that noticeable until you start getting out to longer ranges. Inside of 500 yards it’s pretty negligible. If you can hit reliably at 400 yards you should have no issues killing a pronghorn. Of the dozens I’ve killed only one or two have been beyond 400 yards and that was because I wanted to shoot that far not because I had to.
     
  18. H&Hhunter

    H&Hhunter Moderator Staff Member

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    Oh and BTW thank you folks for giving me an excuse to find and use my once standard issue E6-B flight computer. Believe it or not I once used this little rascal to compute any and all navigational, performance, fuel burn and wind drift calculation while flying a DC-8 around the world and it wasn’t all that long ago!
    F8AB2D03-5C65-4E16-9A61-521C14EFFB8D.jpeg
     
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  19. ms6852

    ms6852 Member

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    I would just re-zero. The rifle is making a long trip and will get bumped around. Not sure if you are driving or flying but if you are flying that can stress the rifle even more especially if the stock is would as cabin pressures and temperatures are different from where you are seating. You are making an expense already to go on a hunt in Wyoming, don't ruin the chance of success because you don't re-zero and confirm. You will hate your self for not doing it if you miss a shot. Don't be lazy about this.
     
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  20. H&Hhunter

    H&Hhunter Moderator Staff Member

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    Always check zero after traveling.
     
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  21. jmr40

    jmr40 Member

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    Most of the online ballistics calculators have the ability to plug in environmental conditions to calculate bullet drop. This is the one I use. In the basic format it doesn't allow you to enter that data, but the more advanced format does. You can go to one of these sites and enter data and change altitude to see the difference in bullet drop. For most shooters at typical ranges altitude alone won't be enough to cause a miss. But interesting to look at.

    https://www.hornady.com/team-hornady/ballistic-calculators/#!/4dof

    The temperature is probably the biggest factor. It not only changes air density, but changes the muzzle velocity. All powders shoot slower in colder temperatures. Some more than others. With some powder expect 1-3 fps velocity change for each one degree temperature change. Other more temperature stable powders may only change 1/2 fps for each one degree temperature changes. A load developed at 70 degrees will be 25-150 fps slower at 20 degrees depending on the powder used.
     
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  22. Ole Joe Clark

    Ole Joe Clark Member

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    You gotta watch that high altitude shooting, that thin air and gravity might allow the bullet to fly high. :)

    Have a blessed day,

    Leon
     
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