density altitude

Discussion in 'Long Range Hunting & Shooting' started by trueblue, Jan 4, 2011.

  1. trueblue

    trueblue Well-Known Member

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    Feb 18, 2008
    Is anyone using density altitude cards for there come ups as a backup to their electronics and PDA?
     
  2. EXPRESS

    EXPRESS Well-Known Member

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    Jun 25, 2003
    Hey Trueblue, density altitude is possibly the single most important factor in exterior ballistics predictions. However unfortunately outside of aviation circles it is not widely known or understood, nor is it used by software, making it essentially pointless.

    DA gives us the effective resistance of the air on the bullet given the temperature, atmospheric pressure, altitude and humidity. Most programs must combine these factors if you enter them in, and make something similar to a DA calculation, but as a stand alone factor it could be viable replacement for the weather based variables we input.

    By all means, use a Kestrel 4000 and log DA when shooting and you will be able to determine how your load performs in different places at different times of year, at different altitudes and temperatures with more accurately than by temperature and altitude alone.
     

  3. MMERSS

    MMERSS Well-Known Member

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    Feb 5, 2013
    "300 RUM, DA3000, 10MPH"

    0400 -0002.2 -001.5 0700 -0010.0 -002.8 L1
    0410 -0002.5 -001.5 0710 -0010.3 -002.8 L1
    0420 -0002.7 -001.6 0720 -0010.6 -002.9 L1
    0430 -0002.9 -001.6 0730 -0010.8 -002.9 L1
    0440 -0003.2 -001.7 0740 -0011.1 -003.0 L1
    0450 -0003.4 -001.7 0750 -0011.4 -003.0 L1
    0460 -0003.6 -001.7 0760 -0011.7 -003.1 L1
    0470 -0003.9 -001.8 0770 -0012.0 -003.1 L1
    0480 -0004.1 -001.8 0780 -0012.3 -003.2 L1
    0490 -0004.4 -001.9 0790 -0012.6 -003.2 L1
    0500 -0004.6 -001.9 0800 -0012.9 -003.3 L1
    0510 -0004.9 -001.9 0810 -0013.2 -003.3 L1
    0520 -0005.1 -002.0 0820 -0013.6 -003.4 L1
    0530 -0005.4 -002.0 0830 -0013.9 -003.4 L1
    0540 -0005.6 -002.1 0840 -0014.2 -003.5 L1
    0550 -0005.9 -002.1 L1 0850 -0014.5 -003.5 L2
    0560 -0006.2 -002.2 L1 0860 -0014.8 -003.6 L2
    0570 -0006.4 -002.2 L1 0870 -0015.1 -003.6 L2
    0580 -0006.7 -002.2 L1 0880 -0015.5 -003.7 L2
    0590 -0006.9 -002.3 L1 0890 -0015.8 -003.7 L2
    0600 -0007.2 -002.3 L1 0900 -0016.1 -003.8 L2
    0610 -0007.5 -002.4 L1 0910 -0016.4 -003.8 L2
    0620 -0007.7 -002.4 L1 0920 -0016.8 -003.9 L2
    0630 -0008.0 -002.5 L1 0930 -0017.1 -003.9 L2
    0640 -0008.3 -002.5 L1 0940 -0017.4 -004.0 L2
    0650 -0008.6 -002.6 L1 0950 -0017.8 -004.0 L2
    0660 -0008.8 -002.6 L1 0960 -0018.1 -004.1 L2
    0670 -0009.1 -002.6 L1 0970 -0018.5 -004.1 L2
    0680 -0009.4 -002.7 L1 0980 -0018.8 -004.2 L2
    0690 -0009.7 -002.7 L1 0990 -0019.2 -004.2 L2
    1000 -0019.5 -004.3 L2

    Yes I do and here is an example. My ballistics engine allows for an input for density altitude to correspond to a specific air density. I use the Kestrel 4000 to compute density altitude. DA is easy to use and only requires one input unlike many ballistics engines that require input of baro pressure, altitude, temp and humidity. Both methods produce the same results however only the DA method requires one input.
     
  4. EXPRESS

    EXPRESS Well-Known Member

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    Good news, so what is the software you use?
     
  5. JeffVN

    JeffVN Well-Known Member

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    Mar 19, 2004
    I use DA. The "Shooter" app for Android uses DA as one of the inputs for calculating its solutions.

    Jeffvn
     
  6. Coyboy

    Coyboy Well-Known Member

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    Jan 30, 2005
    Jim, yes I print out a set of cards that range about 3000' in DA above and below the actual elevation I will be shooting at. I then confirm DA during the day with a Kestral. If you shoot an area often enough and your kestral goes down, you should have gleaned enough local knowledge to swag out a pretty good estimate of the DA based on past experience.