Altitude and its effects

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by thunderchicken, Aug 21, 2008.

  1. thunderchicken

    thunderchicken Active Member

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    I will be hunting out west for the first time in October. Being from Alabama and having an altitude of around 600ft I am concerned about bullet impact once my rifle is shot in the higher altitude. Of course I will shoot my rifle once I arive in CO but my question is this. If I zero my rifle at 100yds at 600ft altitude what should I expect my bullet to do at 8000 to 10000ft? I know it will climb but how much? Our humidity in Alabama is also high right now it stays at around 70% or higher (90% here latley) so that will have an impact as well. I know from a short range standpoint not much will change but if I were to zero at 200 (like I normaly do) what would I expect as well. I am shoot a 7mm factory loaded Fed. Prem. with a 160 accubond.
     
    Last edited: Aug 21, 2008
  2. grit

    grit Well-Known Member

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    I could do it for you, but... If you go to the bullets, barrels, and ballistics section you will find a thread at the top - ballistic programs, web based and downloadable. I like the one with eskimo in it. Click the link, put in your data, hit calculate, and save. Then do it again changing the elevation, humidity, whatever else you think'll change. Now you can answer these questions whenever you want. Take a look. You'll have more questions.
     

  3. milanuk

    milanuk Well-Known Member

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    Humidity matters so little as to be negligible. Play around with the aforementioned ballistics progams and you'll see what I mean.

    Altitude matters quite a bit, but you might be time/money ahead to get an altimeter/barometer like a Kestrel 4000 (other models work, its just what I happen to have)... what changes is the barometric pressure (gets less with higher altitudes), but it can change in some weird ways due to local conditions, terrain, etc. so it can help to know what it actually *is*, not just what it 'should be' for a given altitude. Of course, then a PDA becomes pretty helpful... and the list goes on ;)

    In general, you're going to start seeing a noticeable decrease in drop out past 400yds. My 1k zero for a .308 Win 155gr VLD @ 2960fps changed from 31 moa @ 800' ASL to 24' moa @ 6600' ASL.

    Monte
     
  4. Black Diamond 408

    Black Diamond 408 Well-Known Member

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    You better have a good balistic program like Exbal to reference. I sighted in my rifle here at 1400' and took it to 6000 and it still was dead on at 100yds, from there you need a program that will calculate the elevation changes. The Eskimo program works well for a general drop chart, but hard to input changes if its not with you. My rifle has a drop of 17 moa @ 1000yds where i live in Neb. The same loads in Wyo at 6000' changed to 15.5 moa, 1000yds. I made drop charts before i left home and found they were close, but not close enough when your talking long ranges.

    There is no substitute for real testing. I have found Exbal to be very acurate as long as you know all the weather perameters.

    Dave
     
  5. shortshooter

    shortshooter Well-Known Member

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    There is a sticky in bullets, barrels, ballistics about this and it's good information.

    The way I understand it is that you want humidity and absolute pressure ( not corrected pressure). You enter an 0 for the altitiude value. It appears that more than anything drag is the real issue.

    Anyway this is what I walked away from after reading that post.

    As said, you should be throwing a few bullets at you designated altitude to see whats going on . After all the proof is in the puddin.
     
  6. kcebcj

    kcebcj Well-Known Member

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    Just ran your load in Exbal and here is what comes up.At 200 yards the drop from the bore is 7.8 inches at sea level. At 8000 ft elevation the drop from the bore is 7.6 inches. There is .2 of an inch difference. In my opinion not enough to give a second thought for regular hunting out to 400 yards or so. If you shoot beyond that I would resight the rifle at alitude and have a drop chart made for the alitude that your hunting at. If nothing else the darn gun will shoot better the higher you get. Have fun.
     
  7. James H

    James H Well-Known Member

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    That's almost like cheating :D

    You must be talking about the .338 Cheytac.

    James
     
  8. Black Diamond 408

    Black Diamond 408 Well-Known Member

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    Hmmmmmm, Cheating? Just more dead... lots more faster! 338 Snipetac
     
  9. MontanaRifleman

    MontanaRifleman Well-Known Member

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    Elevation or wind or angle, etc. will have very little effect inside 200 yds. The farther out you get the more effect it will have (exponentially).

    As said previously, there is no substitute for practice in actuall conditions when it comes to LR.

    Good hunting
     
  10. thunderchicken

    thunderchicken Active Member

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    I would like to thank everyone who responded to my post. The information has been found very usefull and I now have information thanks to you that will leed me to the right answers or at least a starting point. I had asked the same question to those individuals around these parts that are supose to be benchrest know it alls and gun experts and I just keep getting the look that a dog has when you set a new water bowl down in front of him.