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MOA ... Do I have this right?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/20/2006 at 15:11
macky View Drop Down
Optics Apprentice
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I'm sure I'm starting at a pretty basic place, but I just want to make sure that I have my info right rather than build my foundation on sand ...

 

So I read that "defined loosely, one MOA equals 1" at 100 yards, 2" at 200 yards, 3" at 300 yards, etc (the one inch is really 1.047197580733") ..... then I read about scopes that have 1/4 MOA, 1/2 MOA, etc, adjustment knobs.  So if I have this right, and I have a scope with 1/2 MOA adjustment knobs, then each click on the knob is a 1/2" increment at 100 yards, 1" increment at 200 yards, 1 1/2" increment at 300 yards .... and at 500 yards each click on the knob is a 2 1/2" increment on my target .... is 1/2" a fairly acceptable increment?  I guess if you were shooting field mice at 500 yards you might want better   

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/20/2006 at 15:31
Infidel View Drop Down
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Yes, you have it right.  I (and others) tend to get sloppy with the terms, and use "minutes" when I should say "inches at 100 yards" and vice-versa.  Some places you will see "shooter's minutes of angle" to refer to 1" at 100 yards, and "true minutes of angle" to refer to ... well, ... true minutes of angle.  Most scopes' adjustments are in fractions of inches at 100 yards.  The most popular click values are 1/4" and 1/8".  1/2" is faster to adjust for different distances, but not as precise. 


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/20/2006 at 15:43
macky View Drop Down
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Thanks .... is there a finite number of clicks on an adjustment knob.  Meaning, if you have a 1/8 MOA click knob and lets say (for discussions sake) that the knob has 80 rotational clicks (40 in each direction from 0) .... then 80 x 1/8 = 80/8 or 10 MOA .... then that scope can compensate 5 MOA higher and 5 MOA lower .... or 5" low to 5" high at 100 yards, and 2 1/2" lower to 2 1/2" higher at 500 yards?  At I way off on the number of rotational clicks on a scope?  (I think I hope so)
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/20/2006 at 18:11
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You are a bit off on the number of clicks.  Scopes are typically speced out for a certain adjustment range which is normally defined in inches at 100 yards.  For example, for a SIghtron S2 4-16x42MD scope that I have the adjustment range is advertised as 56 inches at 100 yards.  That means that once the scope is centered mechanically (both windage and adjustment knobs are set to the centers of their adjustment ranges) I can adjust the scope to aim 28inches higher or lower and 28 inches to the left or to the right.

 

This particular scope has 1/8" adjustments which translates into 448 clicks of total adjustment range or +/-224 clicks from the center position.

 

If this scope had 1/4" adjustments, that would be 224 clicks of total adjustment range.

 

If this scope had 1/2" adjustments, that would be 112 clicks of total adjustment range.

 

Most varmint scopes have 1/8" clicks because the targets are small.

 

For tactical scopes, where a shooter often has to dial in a lot of adjustment, but aims at a considerably larger target 1/2" click are most common and there quite a few that have 1" clicks.

 

1/4" clicks are the most common on mid range scopes as they offer a good compromise between mechanical resolution and adjustment speed.

 

ILya

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/20/2006 at 19:45
Infidel View Drop Down
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Macky, you have it right again, most of your arithmetic is fine.  Except that most scopes have more than 40 clicks per revolution, and more than one revolution.  So, for instance, a scope with 1/4" clicks might have 72 clicks perrevolution, which is 18" at 100 yards for each revolution, and it might have almost but not quite 4 revolutions, providing 68 inches of total vertical adjustment (34" up and 34" down from the mechanical zero).

Originally posted by macky macky wrote:

....then that scope can compensate 5 MOA higher and 5 MOA lower .... or 5" low to 5" high at 100 yards, and 2 1/2" lower to 2 1/2" higher at 500 yards?


There's a problem with this arithmetic.  If the adjustment is 5" at 100 yards, then it will be 5 times that, or 25" at 500 yards, 30" at 600, 50" at 1000.

In my previous example of 68 total 34" each way adjustment range at 100 yards, that's 340" each way, 680" total at 1000 yards.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/21/2006 at 08:48
Dale Clifford View Drop Down
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Back when the Sumarians were measuring the amount of wheat and barley they wanted to buy to make their beer, the basic math base was base 60 which was later applied to 2 pi radians. A 2 pi radian sweep is 360 degrees of arc or a complete circle, or two hemisphere folded in half, or the sum of two squared euclidean parameters, x and y one a real root and 1 imaginary. Since the interger math didn't give a whole real root- it was easier to use a division of (yup) base 60. Thus 60 sec equals 1 min- 60 mins. equal 1 hr.- 60 hours equals one long work week and time for a beer. (24 hours is actually 2 modulo 12).
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/23/2006 at 13:38
Urimaginaryfrnd View Drop Down
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The moral to this story is that if you are shooting field mice at 500 yds you need to walk closer.

 

Most Scopes come with 1/4 moa adjustment. Some target scopes come with 1/8moa adjustment.

My Leupold Mark 4 10x M3 has 1/2moa windage and 1moa elevation so it is perfect to put a round center mass at that 500yds but hit a mouse no. The rifles I own are about 1moa to 1/2 moa guns at best, but if you have a spare $3500.+ you can get a 1/4 moa gun from http://www.gaprecision.net/        or   http://www.tacticaloperations.com/

 

and then you have to factor in the wind.      http://www.snipercentral.com/308.htm

 

Needless to say your ammo has to be same bullet  same load all the time. Keep a notebook. Practice!

 

 

 

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/23/2006 at 20:05
Dale Clifford View Drop Down
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another moral might be the best laid plans of mice and men aften go agla. Almost any remington in a .22 cal with a good 1/8" clicks and 1/8" crosshair with good handloads will shoot 1/4 " groups. --for about $700.
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