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Rifles, Reloading, Optics, Equipment
Long Range Scopes and Other Optics
Nightforce NXS- Kenton Industries BDC Military spec turret.
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<blockquote data-quote="Buffalobob" data-source="post: 264279" data-attributes="member: 8"><p>There are two principle adjustments to make to a BDC knob once it is "engraved".</p><p></p><p>In the world of air pollution control and smoke stack design is a set of peculiarities known collectively as the adiabatic lapse rate. Put simply, the higher up you go the thinner the air and the colder it is. So as you increase your altitude the bullet will strike higher from less dense air if the temperature is the same. But colder temperature makes air denser so the bullet will strike lower at a given altitude if it is colder.</p><p></p><p>So here is one example of what I include at the top and or bottom of all of my drop charts for my particular rifle and for my particular bullet.</p><p></p><p></p><p></p><p>What you see is that the drop table was run in the computer with a setting or 5175 feet of altitude and a temperature of 60 degree Fahrenheit. I then change the temperature by 10 degrees while holding the altitude constant and determine how much that affected the bullet strike at 1000 yards and make a note that it affects the bullet strike by one inch or a change in the dial of 0.1 inch/MOA. Then I reset the temperature back to original setting and change the altitude by 1000 feet and check to see how the bullet strike is at 1000 yards and record that as a change in drop which is 0.2 inches/MOA.</p><p></p><p>Those two factors can be ratioed by distance if you wish such that at 500 yards the factors would be half and at 2000 yards the factors would be doubled. Also if you are expecting 60 degree temperature but it is 30 degrees colder then multiply by three. Ratioing will not be extremely precise due to the nature of ballistics but if you stay withing reasonable distances and changes it will be fine because the adjustments are small.</p><p></p><p>You must keep track of positive versus negative change because under normal situations temperature will be subtracted from altitude. Also things change during the day.</p><p></p><p>In summary temperature and altitude are the two principle factors and you should determine them for you bullet and your hunting area. Only you know the range of extremes you can expect to encounter. </p><p></p><p>The process might even work if you use meters and centigrade. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite8" alt=":D" title="Big Grin :D" loading="lazy" data-shortname=":D" /></p></blockquote><p></p>
[QUOTE="Buffalobob, post: 264279, member: 8"] There are two principle adjustments to make to a BDC knob once it is "engraved". In the world of air pollution control and smoke stack design is a set of peculiarities known collectively as the adiabatic lapse rate. Put simply, the higher up you go the thinner the air and the colder it is. So as you increase your altitude the bullet will strike higher from less dense air if the temperature is the same. But colder temperature makes air denser so the bullet will strike lower at a given altitude if it is colder. So here is one example of what I include at the top and or bottom of all of my drop charts for my particular rifle and for my particular bullet. What you see is that the drop table was run in the computer with a setting or 5175 feet of altitude and a temperature of 60 degree Fahrenheit. I then change the temperature by 10 degrees while holding the altitude constant and determine how much that affected the bullet strike at 1000 yards and make a note that it affects the bullet strike by one inch or a change in the dial of 0.1 inch/MOA. Then I reset the temperature back to original setting and change the altitude by 1000 feet and check to see how the bullet strike is at 1000 yards and record that as a change in drop which is 0.2 inches/MOA. Those two factors can be ratioed by distance if you wish such that at 500 yards the factors would be half and at 2000 yards the factors would be doubled. Also if you are expecting 60 degree temperature but it is 30 degrees colder then multiply by three. Ratioing will not be extremely precise due to the nature of ballistics but if you stay withing reasonable distances and changes it will be fine because the adjustments are small. You must keep track of positive versus negative change because under normal situations temperature will be subtracted from altitude. Also things change during the day. In summary temperature and altitude are the two principle factors and you should determine them for you bullet and your hunting area. Only you know the range of extremes you can expect to encounter. The process might even work if you use meters and centigrade. :D [/QUOTE]
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Nightforce NXS- Kenton Industries BDC Military spec turret.
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