Grey2112,
This can can a bit scientific but here goes. First the concept of what "Minute Of Angle" MOA is and how it affects the bullet's dispersion pattern as ranges are increased must be understood. I found this on a disk website and I believe it is close and can be helpful.
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True Minute Of Angle, MOA, is measured by first determining the minutes of angle in a circle. We know that a circle contains 360 degrees and that there are 60 minutes in each degree. The minutes of angle in a circle is 360 x 60 or 21,600. The circumference of a circle is 2 x p x R where R is the radius of the circle in inches. Hence, for any range R, a minute of angle equals 2 x 3.1416 x R divided by 21,600 or .000291 x R.
Therefore, if the range R is 100 yards, a minute of angle would be .000291 x 100 x 36 or 1.0476 inches. Because the distance covered at 100 yards is so close to being exactly 1 inch, the fraction is usually disregarded for range work, and we commonly say that a minute of change on the rear sight will move the point of impact 1-inch at 100 yards. If we were shooting at 1,000 yards, a minute of angle would cover .000291 x 1000 x 36 or 10.476 inches. The difference between the true minutes of angle and the rounded minutes of angle becomes greater as the range increases.
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So basicly 1 MOA equals = 1.045 inches at 100 yards, and increases as the range increases. Most round it to 1 inch - 1 MOA just to ease the process. And except at the "benchrest or at extremely long ranges" the 1" works fine. At least for me anyway. Examples: 200 yards = 2 MOA, 300 yards = 3 MOA... so forth and so on. 500 yards is 5 minute of angle MOA.
To find the theoretical increase in elevation at 100 yards to hit line of sight - point of impact from 200 to 500 yards, divide the range by "100" and you get the MOA for that range. 500 yds is 500/100=5 MOA, 450/100= 4.5 MOA, 475/100=4.75 MOA etc etc. Just think of MOA as one inch, it makes it easier.
If your bullet drop at 500 yards is 62", then divide 62" by 5 MOA and you get 12.4" or 62"/5MOA=12.4". Given this ballistics input(AKA: Dope), if you zero your sight at 100 yards to impact 12.4" high, you theorectically should hit point of impact - line of sight at that range.
That is what the reticle takes into account in the scope. You wrote,
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At the bottom it shows the reticle with standard corrections at 100 yards of 1.5" at 200, 4.5" at 300, 7.5" at 400, and 11" at 500 yards.
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I compute similar data below manually.
Range - Bullet Drop - MOA
100 - zero point of impact - line of sight
200 - -3.3" 1.65" below line of sight
300 - -13" 4.3" below line of sight
400 - -32" 8" below line of sight
500 - -62" 12.4" below line of sight
In order to correct for the bullet drop at the farther ranges, simply zero your weapon at 100 yards, then crank the scope up the appropriate amount of MOA's or inches from above chart, and you can reasonably be expected to hit at the given farther ranges.
The plex reticle you mentioned does this for you. You can see that the plex formula you provided above, does basicly the same thing that I have done manually in my chart.
I don't like using holdover, mildots or stadias, I much prefer what we call, "cranking in the ballistics dope" to achieve a "line of sight - point of impact" hit. That way, my reticle cross hair never leaves the desired point of impact.
You can also use the same method for determining the exact hold off for wind drift. Stadias and mil-dots can also be set-up to provide for that as well. But that is another thread.
The Bullet Drop Compensator BDC, does the same thing as above. It is pre-adjusted, geared I believe, and measured for the ballistic characteristics of a given round. All you need to do is estimate the range... crank to that range on the elevation turret, hold center and squeeze. Given a no wind situation of course.
Finally, what ever ballistics dope you use, or method of acquiring and then applying that dope for the given load... you must then go to that "given" range, to confirm that it is actually right for your set-up. Then adjust, record for later use, and then practice, practice!
Know this: temperature, humidity, altitude, and even the distance to target all serve to change this dope in day to day varying conditions. I suggest that you keep a solid accurate record of your results each and every range visit, recording those variables. Then you will have built a solid mechanism for returning to the "line of sight - point of impact" desired under varying conditions and ranges.
I know this was wordy, and hope it is helpful.
Many more here probably have a better way of explaining this than I. Good luck.
v/r
CG