How an MOA is measured

J_Roger

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Ok guys, here's one for ya. We all know that an MOA is an inch point whatever at 100 yards, and we all talk about shooting at least an MOA with our rifles, but how do you really measure MOA accuracy? One MOA at 100 is an inch BUT if I'm aiming dead center at a target and my round impacts one inch from center, is that not 2 MOA? Here's my reasoning. One MOA at a 100 would be a one inch but wouldn't that be an inch diameter, and therefore a half inch radius circle around the center? So to shoot one MOA, your rounds must be at most half an inch from the center? What do you think?
 

NOMAD

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  • Oct 7, 2001
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    Re: How an MOA is measured

    Devil dog you are over thinking this!!

    To determine the accuracy of your gun by measuring the group measure the size of the group center to center of your bullet holes and you can now say your gun shoots ABC size group!!

    The location of the impacts on your target has nothing to do with the measuring of accuracy of the group.

    The hits on target can be a product of a bad zero or changing environmental conditions or a host of other things.

     

    Ol' RD

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    Re: How an MOA is measured

    What he said!
    whistle.gif
     

    threetrees

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    Re: How an MOA is measured

    the difference between precision and accuracy:

    Accuracy-and-precision-picture.png


    offset is not important - it can be compensated/fixed via the reticle.

    but the 'width'/spread not - that's what you have to live with. that's where your markmanship and the quality of the rifle comes in.
     

    tnichols

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    Re: How an MOA is measured

    My dumb farm boy way of thinking it is, if a rifle will consistantly shoot 5" groups at 500 yards, it's a MOA (or slightly better) rifle. Don't mind f^#K it, just get out and shoot and play in the wind, and have fun.
     

    sandwarrior

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    Re: How an MOA is measured

    For groups you measure center to center of outside (farthest apart)shots.

    For measuring MOA on a lone shot on a target, you measure bullet center to point of aim. If you hit one inch right then you made the shot @ 1 moa. You don't add the opposite side.
     

    Graham

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    Re: How an MOA is measured

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: J_Roger</div><div class="ubbcode-body">One MOA at 100 is an inch</div></div>1 MOA equals 1.047 inches at 100 yards. A 5% error is significant at distance.
     

    Sterling Shooter

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    Re: How an MOA is measured

    At distance it's moot, going to distance it's important, as in from a 100 to 1000 yard zero. For example, making a zero refinement at 1000 yards, you can forget the .047; however, from 100 to 1000 with true MOA yet thinking in inches could be a pretty big error, about 18.8 iches based on a 40 MOA come-up.
     

    threetrees

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    Re: How an MOA is measured

    the precision is kind of an errorbar. when someone argues about 5%, they are talking of an error on an error bar ... when you go through the maths/statistics in detail, you'll see that the error on the precision/moa derived from 3-5 shot groups is larger than those 5% and, from my point of view, can be ignored in most cases.

    for instance: do you define the precision/moa by full-width-half-maximum? 1/e? or ... 1/2/3 sigma? probably most interesting would be 3 sigma - then you have an area where your shots should be with a confidence of 99.7%. but noone wants to give that number.

    -----------------

    short: make 5 shots, get largest distance between centre of holes. take that as an estimate.

    moa is 'minute of angle' -> given a distance r, the circumference is: 2*pi*r (circumference); this corresponds to 360 degrees, each degree having 60 minutes.

    so the 'length' of one moa at a distance r is: 2*pi*r / (360*60)

    take the measured max spread, divide by the above length of one moa at a distance r and you got your moa-estimate.

    -----

    additional comment on what sterling said: there are two conventions used:

    a) moa in the sense of impact distribution / the precision of the combo the rifle+you+environment.

    b) the other one is compensation for bullet drop when going from one distance to another.

    in case a) moa is used in terms of precision (spread of impacts) - a 5% error here does not really matter
    in case b) moa is used in terms of accuracy (shift of the mean); 5% can be significant here.
     

    sandwarrior

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    Re: How an MOA is measured

    Wow...we need to make this difficult.

    An MOA is 1.047" or 1.05" for short @ 100 yds. Another way 1"- PHY +5%. Unless you are shooting benchrest accuracy that .050" isn't going to matter. Most times even in benchrest it doesn't. Now, at 1000 yds. that is times ten, or 10.47". So, as you see it, or measure it after the bullets strike the target, .47" or 5% isn't going to make a hill of beans.

    Where it becomes critical is when you adjust your sights
    (scope). If your sights adjust in inches (IPHY) then you lose that 5% per inch of adjustment. So, if it takes 34 MOA to get you to 1k, but you adjusted up 34" you are going to be that 5% low, or 17" low. Holding center mass on a full size target you will get a hit. If shooting center mass on a half size torso you will get a miss. Windage will be off as well but not as bad.

    So, getting back to what the original question was, if you hit within one inch-per hundred yards, i.e., bullet strike 4" away from center @ 400 then you've gotten within an MOA of your target. Even with the differences the same applies to an MOA away 4.188", you come within an MOA.
     

    BadDudes4Hire

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    Dec 22, 2011
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    Re: How an MOA is measured

    First, get an understanding of elevation. Understand your ballistics for the particular round you are using. Okay. At 100 yards, your bullet will drop so much, then more at 200 and so on. Second, get an understanding of your windage. Again, know your specific ballistics for that particular round. The heavier (more grains) the round, the less windage you will incur, in most cases. Now, there are many threads on these 2 topics alone. Lets remove these topics and lets talk MOA. Most guys here have told you that the 1 Minute of Angle is 1.047 inches at exactly 100 yards. That is 2.094 inches at 200 yards. That is 4.188 inches at 400 yards. 8.376 inches at 800 yards, and 10.47 inches at 1000 yards. If the bore of your rifle shot a "laser bullet" that didnt drop, or didnt get affected by wind, it would be exactly 0 MOA at 1000 yards. Let that be the Center of the cone. Imagine a cone around that centers this laser shot. If you were off by 1.047 inches at 100 yards, then draw a circle around that first laser center shot, the bullet would be off 2.094 inches at 200 and so on til off 10.47 inches at 1000 yards. Keep drawing circles at so many x00 yards. This would be 1 MOA. MOA is a degree, like in 360 degrees of a circle. That circle would be proportionate at each x00 yard length. I hope this makes sense so far. Now you have your cone. You can see that in any direction you miss 1.047 inches, your cone proportionate to however many yards from that first laser center shot. Now, put your ballistics back in the picture, 1 -drop and 2- windage. 1 moa is considered decent in terms of long range accuracy. If you are 2 MOA off at 1000 yards you are off 20.94 inches in any direction from center.
    TaDa - MOA
     

    bigwheeler

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    Re: How an MOA is measured

    I think you meant an moa is 1/60 of one degree of a circle. degrees, minutes and
    seconds. They've been around in navigating, star mapping and surveying for longer
    than any of us.
     

    BadDudes4Hire

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    Re: How an MOA is measured

    Yeah, I just didnt want to go into the specifics of the degrees, of a circle, when I was really concentrating on the MOA aspect, and using a circle proportionate out from that, making a cone. That is correct, sorry for not specifying. Been around for awhile, they have. Thanks for catching that, as others porbably saw that as well.
     

    Sterling Shooter

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    Re: How an MOA is measured

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: J_Roger</div><div class="ubbcode-body">Ok guys, here's one for ya. We all know that an MOA is an inch point whatever at 100 yards, and we all talk about shooting at least an MOA with our rifles, but how do you really measure MOA accuracy? One MOA at 100 is an inch BUT if I'm aiming dead center at a target and my round impacts one inch from center, is that not 2 MOA? Here's my reasoning. One MOA at a 100 would be a one inch but wouldn't that be an inch diameter, and therefore a half inch radius circle around the center? So to shoot one MOA, your rounds must be at most half an inch from the center? What do you think?</div></div>

    The literal definition of hitting where aimed is when the bullet path intersects line of sight, where the resulting value in any form of measurement is zero. Since most of us can not realize zero dispersion, that's to say, put em all in the same hole, we shoot a group and triangulate it to determine the center for the purpose of adjusting the sights to hit where aimed. We can also use the triangulated center of a group to create a radius which encompasses our group; and, this can be used to provide a value for our group in MOA if we wish. Once zeroed, we can use the MOA unit of measurement for all sorts of things, like range-finding, wind counters, and elevation adjustment to distance, where a singular bullet is accepted as evidence of a zero, or where the rifle was pointed.