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Velocity and Altitude question

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  #1  
Unread 03-31-2014, 07:22 PM
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Velocity and Altitude question

I live 500' above sea level and hunt at 9000-11500 feet. I know ballistics change with altitude, but I'm wondering if velocity does too. If I recall correctly, if I'm shooting 3280 at 500' elevation, at 11000 or so, the velocity should be higher. I guess the sure way to know is shoot the gun through my chrony at somewhere close to that altitude, but I can't do that until I go back in October.

Or, do I put the parameters into the ballistics calculators and do they do the math for me?
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  •   #2  
    Unread 03-31-2014, 09:18 PM
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    Re: Velocity and Altitude question

    Velocity change in the barrel due to elevation is not a factor. A chrony 15 Ft away will probably be well within your ES to and not a factor.

    If you use an app like Shooter, it calculates the altitude change for you based on the altitude/temp/pressure where you sighted in at.


    It is a very good idea to actually do some practice shots and verify everything at the altitude you will be hunting at anyway IMHO.
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      #3  
    Unread 03-31-2014, 11:35 PM
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    Re: Velocity and Altitude question

    It's an INTERNAL ballistic factor and wouldn't be accounted for in any EXTERNAL ballistic math.
    I know it can affect tune. I don't know about muzzle velocity.
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      #4  
    Unread 04-01-2014, 12:28 PM
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    Re: Velocity and Altitude question

    Quote:
    Originally Posted by Barrelnut View Post
    Velocity change in the barrel due to elevation is not a factor. A chrony 15 Ft away will probably be well within your ES to and not a factor.

    If you use an app like Shooter, it calculates the altitude change for you based on the altitude/temp/pressure where you sighted in at.


    It is a very good idea to actually do some practice shots and verify everything at the altitude you will be hunting at anyway IMHO.
    Thanks for the info.

    I always shoot my guns when I arrive and reconfirm zero.

    My main reason for asking is I was going to have some turrets made with the drop built in. I'm just trying to make it the best I can before I go ahead with it.
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      #5  
    Unread 04-01-2014, 12:30 PM
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    Re: Velocity and Altitude question

    Quote:
    Originally Posted by Mikecr View Post
    It's an INTERNAL ballistic factor and wouldn't be accounted for in any EXTERNAL ballistic math.
    I know it can affect tune. I don't know about muzzle velocity.
    I don't understand. Can you explain more?
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      #6  
    Unread 04-01-2014, 11:38 PM
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    Re: Velocity and Altitude question

    Well, different air density being pushed down a bore could affect the pressure curve a bit, affecting your accuracy. But there are a lot of variables to internal ballistics that could ultimately sum to actual muzzle velocity change -or not.
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      #7  
    Unread 04-02-2014, 04:19 AM
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    Re: Velocity and Altitude question

    You are not likely to see a big change, if any in muzzle velocity, but it's still advisable to re-zero when changing locations of different altitudes. The difference in the altitude/air density, will produce a lower resistance on the bullet, producing higher retained velocities at longer ranges, thus requiring a lower elevation correction at those longer ranges. a ballistic program , like Shooter will provide the corrections when the air density/altitude info is inputed for the higher elevation.
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