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Rifles, Reloading, Optics, Equipment
Long Range Scopes and Other Optics
MilDot Calculations and zoom
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<blockquote data-quote="gperry99" data-source="post: 287032" data-attributes="member: 17901"><p>A brief review of the basics is in order. First the spacing between reference bars of a reticle located in the 1st focal plane do not change with operating power of the scope but the lines get darker and thicker as you decrease power from the calibration power. Secondly, for reticles in the 2nd focal plane the spacing between the reference bars changes by the ratio of the calibration power divided by the operating power. The lower the power the greater the distance between the reference bars. These principles apply to all ranging reticles (MOA, mil radian, inches per 100 yards, and cm per 100 meters). By playing with this ratio it is possible to change 2 MOA spacing to 1 mil radian spacing for example.</p><p> </p><p>If you are using a BDC elevation adjustment dial you need to remember that it is a cam that causes the elevation to change in accordance with the bullet trajectory curve at some standard conditions. The better vendors clearly identify these conditions. If you are shooting at "non standard" conditions you will need to manually dial in a bias value to compensate for the change in base conditions. The current version of Exbal (PC version 9.6) has a feature that will generate BDC quick reference cards that give you the information needed to use either a BDC elevation adjustment, a BDC reticle, or both under varying atmospheric conditions and incline angles.</p></blockquote><p></p>
[QUOTE="gperry99, post: 287032, member: 17901"] A brief review of the basics is in order. First the spacing between reference bars of a reticle located in the 1st focal plane do not change with operating power of the scope but the lines get darker and thicker as you decrease power from the calibration power. Secondly, for reticles in the 2nd focal plane the spacing between the reference bars changes by the ratio of the calibration power divided by the operating power. The lower the power the greater the distance between the reference bars. These principles apply to all ranging reticles (MOA, mil radian, inches per 100 yards, and cm per 100 meters). By playing with this ratio it is possible to change 2 MOA spacing to 1 mil radian spacing for example. If you are using a BDC elevation adjustment dial you need to remember that it is a cam that causes the elevation to change in accordance with the bullet trajectory curve at some standard conditions. The better vendors clearly identify these conditions. If you are shooting at "non standard" conditions you will need to manually dial in a bias value to compensate for the change in base conditions. The current version of Exbal (PC version 9.6) has a feature that will generate BDC quick reference cards that give you the information needed to use either a BDC elevation adjustment, a BDC reticle, or both under varying atmospheric conditions and incline angles. [/QUOTE]
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