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<blockquote data-quote="MMERSS" data-source="post: 785967" data-attributes="member: 63748"><p><span style="font-size: 10px">lever-hed,</span></p><p> </p><p><span style="font-size: 10px">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.</span></p><p> </p><p><span style="font-size: 10px">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. <strong>AIR DENSITY</strong> is the target we are after and can be calculated with the use of our weather stations and ballistics programs. </span></p><p><span style="font-size: 10px">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 <strong>A FEW</strong> weather stations will provide a density altitude option. Both options calculate air density.</span></p><p> </p><p><span style="font-size: 10px">For the long-range shooter we have to ask ourselves the question: "So what with air density?"</span></p><p> </p><p><span style="font-size: 10px">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.</span></p><p> </p><p><span style="font-size: 10px">300 RUM Berger 230, DA3000, 10 MPH</span></p><p><span style="font-size: 10px">Range ELV Wind SD</span></p><p><span style="font-size: 10px">600 7.2 2.3 L1</span></p><p> </p><p><span style="font-size: 10px">300 RUM Berger 230, DA7000, 10 MPH</span></p><p><span style="font-size: 10px">Range ELV Wind SD</span></p><p><span style="font-size: 10px">600 6.9 2.0 L1</span></p><p> </p><p><span style="font-size: 10px">300 RUM Berger 230, DA3000, 10 MPH</span></p><p><span style="font-size: 10px">Range ELV Wind SD</span></p><p><span style="font-size: 10px">1000 19.5 4.3 L2</span></p><p> </p><p><span style="font-size: 10px">300 RUM Berger 230, DA7000, 10 MPH</span></p><p><span style="font-size: 10px">Range ELV Wind SD</span></p><p><span style="font-size: 10px">1000 18.6 3.7 L2</span></p><p> </p><p><span style="font-size: 10px">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?"</span></p><p> </p><p><span style="font-size: 10px">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.</span></p><p> </p><p><span style="font-size: 10px">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! </span></p><p> </p><p><span style="font-size: 10px">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.</span></p></blockquote><p></p>
[QUOTE="MMERSS, post: 785967, member: 63748"] [SIZE=2]lever-hed,[/SIZE] [SIZE=2]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.[/SIZE] [SIZE=2]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. [B]AIR DENSITY[/B] is the target we are after and can be calculated with the use of our weather stations and ballistics programs. [/SIZE] [SIZE=2]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 [B]A FEW[/B] weather stations will provide a density altitude option. Both options calculate air density.[/SIZE] [SIZE=2]For the long-range shooter we have to ask ourselves the question: "So what with air density?"[/SIZE] [SIZE=2]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.[/SIZE] [SIZE=2]300 RUM Berger 230, DA3000, 10 MPH[/SIZE] [SIZE=2]Range ELV Wind SD[/SIZE] [SIZE=2]600 7.2 2.3 L1[/SIZE] [SIZE=2]300 RUM Berger 230, DA7000, 10 MPH[/SIZE] [SIZE=2]Range ELV Wind SD[/SIZE] [SIZE=2]600 6.9 2.0 L1[/SIZE] [SIZE=2]300 RUM Berger 230, DA3000, 10 MPH[/SIZE] [SIZE=2]Range ELV Wind SD[/SIZE] [SIZE=2]1000 19.5 4.3 L2[/SIZE] [SIZE=2]300 RUM Berger 230, DA7000, 10 MPH[/SIZE] [SIZE=2]Range ELV Wind SD[/SIZE] [SIZE=2]1000 18.6 3.7 L2[/SIZE] [SIZE=2]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?"[/SIZE] [SIZE=2]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.[/SIZE] [SIZE=2]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! [/SIZE] [SIZE=2]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.[/SIZE] [/QUOTE]
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