Range card format Help

Discussion in 'Long Range Hunting & Shooting' started by gphil, Mar 25, 2013.

  1. gphil

    gphil Well-Known Member

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    what all is everyone putting on their range cards? Ive been trying to decide how i want to make my range cards efficiently and im struggling. I will be doing my adjustment it MOA. I plan on having:

    vertical adjustment
    horizontal adjustment- just 5mph then ill multiply for various conditions
    potentially angles for every range @ 15, 30, and 45 degrees
    and i would like to make my series of cards with variable temp and pressures
    im just not sure if its safe to substitute "elevations" for pressures

    But i guess im hung up on how people are dealing with atmospheric pressure changes. I feel like a kesterl is the best solution to this problem, but since i dont have one whats my best game plan? I see the ballistic calculator on LRH mag uses various elevations if you print off their set of range cards, and so does JBM. I dont understand atmospheric presssure very well. The higher in elevation the lower the pressure correct? is it safe to base your range cards on average elevations instead of actual pressures? does the pressure stay the same at the same elevation at different seasons? a

    and finally how many people are accounting for spin drift on their cards?

    thanks for the advice!
     
  2. MMERSS

    MMERSS Well-Known Member

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    300 RUM DA1000, 10MPH​


    Range ELV Wind SD
    etc etc etc etc
    1000 18.5 4.5 L2​


    Here is an example of the range cards I use. I know you said you don't have a weather station but they are sure handy with computing the density altitude, they take out most of the guess work. I will have a card for every 1000ft of Density Altitude and take three or four with me for the day depending on anticipated weather changes. Ranges every 10 yards starting around 400 yards up to the maximum range. For COS(X) I will use a calculator if needed. Very simple to use.​
     
  3. gphil

    gphil Well-Known Member

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    pressures can vary quite a bit at the same elevation throughout the year right?
     
  4. MMERSS

    MMERSS Well-Known Member

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    I have seen DA change as much as 4000 feet in the same day, at roughly the same elevation. Most change was due to a drastic change in temperature from early morning temps near 0 F to a mid afternoon high in the upper 60's.
     
  5. gphil

    gphil Well-Known Member

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    thats interesting, I thought that they could change quite a bit, Im glad i checked.

    what does DA stand for?

    when people say elevation they are substituting that for an average pressure value correct?
    for example on here if you print off a series of range cards it gives you various elevations and temps. The elevations are based on the average pressures at the elevations provided arent they?
     
  6. MMERSS

    MMERSS Well-Known Member

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    Density altitude is the altitude of the standard atmosphere (sea level, 29.92 in/Hg, 59F) at which the air density would be equal to the actual air density at the place of observation. If you are standing at sea level with the standards described above and the temperature changes to a higher temperature, lets say 90F, your density altitude would then be greater than sea level or 0 ft.

    I guess you could say DA is the altitude the bullet "thinks" it's flying thru using the standard as reference.
     
  7. gphil

    gphil Well-Known Member

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    alright thanks that helps me alot. so really you almost have to have something to read your pressure and temp to be as accurate as possible.

    So when your inputting data into your PDA or phone in the field as long as you know your pressure you dont need to input your elevation do you ?

    DO you correct for spindrift?
    which kestrel do you use?

    I apologize for the slew of questions this whole correction thing has had be balled up. Ive been playing around a little with shooting jugs and i can make hits at 500 and 600 fairly common but 700 is a totally different ball game it seems. Im thinking part of it is due to not having accurate correction data.
     
  8. MMERSS

    MMERSS Well-Known Member

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    If you look in my example of a chart above you will see SD with a correction of L2. This means there is a correction of left two clicks (1/4MOA scope) for that range or a correction of approximately 5" for 1000 yards to compensate for spin drift.

    I use the Kestrel 4000 specifically this model calculates for density altitude. One input in computer solution using DA vs. multiple inputs for temp, pressure, humidity or altitude.
     
  9. lever-hed

    lever-hed Well-Known Member

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    MMERSS, if I understand this, since I'm no expert mountain hunter, the pressure drops as altitude increases, so from your quote, if all things are equal at sea level, and temperature increases (to 90F), can one expect the pressure goes up? (just trying to understand this better)..:)thanks

    STANDARD ATMOSPHERIC CONDITIONS Elevation (ft) Temp (F) Abs Press (inch Hg) 0 59 29.92 500 57.2 29.45 1000 55.4 28.99 1500 53.6 28.54 2000 51.9 27.08 2500 50.1 27.65 3000 48.3 27.21 3500 46.5 26.79 4000 44.7 26.37 4500 42.9 25.96 5000 41.2 25.54 5500 39.4 25.15 6000 37.6 24.76 6500 35.8 24.37 7000 34 23.99 7500 32.2 23.61 8000 30.5 23.24 8500 28.7 22.88 9000 26.9 22.52 9500 25.1 22.17 10000 23.3 21.82
     
  10. lever-hed

    lever-hed Well-Known Member

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    bad format.. here is better version.. the headings are off but you get the idea:D



    STANDARD ATMOSPHERIC CONDITIONS
    Elevation (ft) Temp (F) Abs Press (inch Hg)
    0 59 29.92
    500 57.2 29.45
    1000 55.4 28.99
    1500 53.6 28.54
    2000 51.9 27.08
    2500 50.1 27.65
    3000 48.3 27.21
    3500 46.5 26.79
    4000 44.7 26.37
    4500 42.9 25.96
    5000 41.2 25.54
    5500 39.4 25.15
    6000 37.6 24.76
    6500 35.8 24.37
    7000 34 23.99
    7500 32.2 23.61
    8000 30.5 23.24
    8500 28.7 22.88
    9000 26.9 22.52
    9500 25.1 22.17
    10000 23.3 21.82
     
    Last edited: Mar 27, 2013
  11. MMERSS

    MMERSS Well-Known Member

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    lever-hed,

    In response to your quote above, generally as temperature increases a lower pressure system moves in to the space and vise versa. Lower pressure assume hotter temps, higher pressure assume cooler temps. I’m not a weatherman but you can usually assume certain aspects regarding temperature and pressure.

    Air density influences the predicted ballistics profile of a projectile in flight. The density of the air is related to the drag of a projectile in flight. An increase or decrease of the air density causes more or less resistance to the forward motion of a projectile. AIR DENSITY is the target we are after and can be calculated with the use of our weather stations and ballistics programs.
    Density altitude is calculating the actual density of the air and then assigning the altitude at which that same air density occurs in the standard atmosphere. Air density calculators do the same and require input of four values common to ballistics programs; altitude or map elevation, barometric pressure, temperature and humidity. Most weather stations will provide the readings for the four inputs as stated above and A FEW weather stations will provide a density altitude option. Both options calculate air density.

    For the long-range shooter we have to ask ourselves the question: "So what with air density?"

    Below is data from two of my field charts for a density altitude of 3000DA (which is the standard air density of .91 kg/m3) and 7000DA (.59 kg/m3). I can say 3000DA and 7000DA on my charts but they equate to .91 and .59 kg/m3 of air density. My Kestrel 4000 does not have an output for air density but does for density altitude. Again, you can consider DA as having an air density value equivalent.

    300 RUM Berger 230, DA3000, 10 MPH
    Range ELV Wind SD
    600 7.2 2.3 L1

    300 RUM Berger 230, DA7000, 10 MPH
    Range ELV Wind SD
    600 6.9 2.0 L1

    300 RUM Berger 230, DA3000, 10 MPH
    Range ELV Wind SD
    1000 19.5 4.3 L2

    300 RUM Berger 230, DA7000, 10 MPH
    Range ELV Wind SD
    1000 18.6 3.7 L2

    As stated in a previous post I have experiences as much as a 4000ft density altitude change in a given day. Looking at the charts with a range of 600 and 1000 yards ask yourself the question "so what?"

    600 yard elevation MOA difference; 7.2-6.9 =.3 MOA or one click on a ¼ MOA scope. You should still hit a ground hog in the belly or head aiming center of mass at 600 yards with a .3 MOA correction on either end.

    1000 yard elevation MOA difference; completely a different story. 19.5-18.6 = .9MOA or 4 clicks on a ¼ MOA scope. You are now approximately 10" in elevation correction error if not compensating for density altitude. Now combine this possible error with your velocity standard deviation!

    I hope this post has helped some. Not compensating for air density at extended ranges can cause enough error for you to not achieve your intended outcome.
     
  12. lever-hed

    lever-hed Well-Known Member

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    OK so ‘density altitude’ is simply the standard barometric pressure at the given altitude(s), I understand this part (shown in the chart in my previous post). Then the ‘real pressure’ or actual pressure is going to be plus/or minus that number depending on the particular weather system in the area. So if you are entering DA that simply gives you a standard pressure (and corresponding air density) irrespective of the weather system at your position, and, contrarily, if you are entering actual altitude, pressure, temp + humidity(from a kestrel for ex.) that is obviously better than just entering DA. So, essentially, your cards are only going to reference the standard pressure/air density for each elevation, which is simply your baseline, as I understand. Temperature and humidity will also have an affect on air density.
    Thanks for the good explanation/rendition..
    Lever

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    Last edited: Mar 28, 2013
  13. MMERSS

    MMERSS Well-Known Member

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    Both options will work equally well.
     
  14. gphil

    gphil Well-Known Member

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    So do you feel that using the DA system is accurate enough to hit deer sized animals cosistently enough to hunt with?