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Altitude and its effects

 
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  #1  
Old 08-21-2008, 02:07 PM
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Altitude and its effects

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 by thunderchicken; 08-21-2008 at 02:10 PM. Reason: forgot info
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Old 08-21-2008, 02:30 PM
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Re: Altitude and its effects

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.
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Old 08-21-2008, 03:01 PM
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Re: Altitude and its effects

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
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Old 08-21-2008, 05:51 PM
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Join Date: Sep 2003
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Re: Altitude and its effects

Quote:
Originally Posted by thunderchicken View Post
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.
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
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Old 08-21-2008, 06:33 PM
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Join Date: Jan 2007
Posts: 139
Re: Altitude and its effects

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.
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Old 08-21-2008, 07:31 PM
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Re: Altitude and its effects

Quote:
Originally Posted by thunderchicken View Post
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.
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.
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Old 08-21-2008, 08:53 PM
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Re: Altitude and its effects

Quote:
Originally Posted by Black Diamond 408 View Post
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.
Dave
That's almost like cheating

You must be talking about the .338 Cheytac.

James
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