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Scope Reticle Mechanism Question

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inthewoods View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote inthewoods Quote  Post ReplyReply Direct Link To This Post Topic: Scope Reticle Mechanism Question
    Posted: August/04/2019 at 05:06
On a 1/4 MOA ejector mechanism, how much movement of the crosshairs equals 1/4 MOA at 100 yards?
inthewoods
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RifleDude View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RifleDude Quote  Post ReplyReply Direct Link To This Post Posted: August/04/2019 at 07:14
Ok, first of all, MOA is an angular measure, not a linear measure, so citing a distance to target is irrelevant. 1 MOA = 1/60 of a degree. The reason you're relating MOA to 100 yards is likely because 1 MOA happens to equate to a deviation of approx 1 inch at 100 yards (1.047" to be exact). Since MOA is an angular measure, that deviation grows as distance increases, so 1MOA translates to approx 2.094" deviation on target @ 200 yds, 5.235" @ 500, 10.47" @ 1000, etc.

So, to answer your question, the linear reticle movement amount to achieve a given correction can vary from scope to scope because since MOA (and Milliradian) is an angular measure, the amount of reticle movement to accomplish a given angular displacement depends on where the reticle is located inside the scope.

But...lets assume for illustration purposes that the reticle is located 6" away from the pivot point of the erector assy (the term is "erector," not "ejector") inside the scope. Since we're dealing with an angular measure, going back to your high school trig, we would then use 6" as the length of the adjacent side of a right triangle and we're wanting to solve for the opposite side of the triangle (the linear reticle displacement). Since 1 MOA = 1/60 of a degree, the acute angle between the hypotenuse and adjacent side of the triangle @ 1 minute of arc is thus .0167 deg.

In that example, to calculate reticle movement, we would then use the formula:
X = 6(tan .0167)...
X = 6(.00029)...
X = .00174" of reticle movement for 1MOA of displacement.

Therefore, in that example, the reticle would need to move .00174/4 or approx .0004" for 1/4 MOA.

Ted


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inthewoods View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote inthewoods Quote  Post ReplyReply Direct Link To This Post Posted: August/04/2019 at 08:03
RifleDude
Much appreciated info. I was guessing .001 to .002".
inthewoods
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