Need help on understanding MOA...

Discussion in 'Competition Shooting Forum' started by Smokin Guns, Oct 16, 2003.

  1. Smokin Guns

    Smokin Guns New Member

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    Another member (myself included) asks this question...

    All I can do with my Romanian is that at 100+yds 15 rounds can put a 9"(diameter, 4.5 radius). Now this is not using the bullseye for the measuring point. My measurement is that all 15 hit in a 9" circle. I never have, until I got on line here while back knew anything about MOA's and stuff like that. Is the MOA measured with a protractor with the bullseye being the start of the MOA or is the MOA the halfway point between the two holes furtherest from each other?

    Y'all got any advice/input/education...;)
  2. Jay

    Jay New Member

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    Greetings SG,

    I'm no teacher, but lets see if I can get this right the first time. (nope, had to edit twice) I'm sure there are folks that can explain it better than I can, but here goes.

    MOA stands for Minute Of Angle. This is a mathematical unit.

    There are 360 degrees in a circle. There are 60 minutes in each degree. One minute of angle is 1/60 of one degree. Visualize it as a triangle with one corner at the muzzle, and the other two corners one inch apart on the target 100 yards away.

    Just by coincidence, one minute of angle is just about 1 inch at 100 yards, (1.0476 inches to be precise), or 2 inches at 200 yards.
    (or 2 x 1.0476 precisely) and so on......

    For the purposes of rifle scopes, the amount of variance from the true measurement of a MOA at 100 yards and 1 inch is so small that it's not worth worrying about.

    Scopes or iron sights with a specification of 1/4 MOA clicks, or some kind of a description which means the same thing, will move the cross hairs or sights about one fourth of an inch with each click that you manipulate the turret knobs. The distance traveled by the crosshairs at 200 yards with each click will be about one half inch. Double the distance to the target and you double the distance each click moves the cross hairs.


    If your rifle can shoot groups 1 inch and under at 100 yds, then you have a "1 MOA rifle".

    There will be no quiz :D

    Hope this helps, Jay
    Last edited: Oct 17, 2003
  3. 45Smashemflat

    45Smashemflat New Member

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    Very good explanation!!

    You can use this info to determine the MOA of various portions of your reticle, such as the width of the thick lines on a Duplex, or the distance between the thick/thin transition and the cross. If you know the MOA, or the "inches it covers up" at 110yds, you can use this as a rudimentary rangfinder.

    Lets say looking at a ruler sitting out at 100yds, you notice that the ruler shows 18" between the top of the thick post and the cross hairs. Any buck whose chest fits between the thick post and the cross is probably 100 yds or closer.
  4. Smokin Guns

    Smokin Guns New Member

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    Thanks to Jay and 45...Good explanation!!! :)
  5. 45Smashemflat

    45Smashemflat New Member

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    Now lets do the same thing for Mils........
  6. Jay

    Jay New Member

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    Not being comfortably versed in this subject, here's a quote from an article, and a link to it, that was written by a gent much more qualified to explain it than I am.........

    "Mil" is short for milli-radian, which is nothing more than a measurement of an angle. Most of us know that there are 360 degrees in a circle, and 60 minutes in each of those individual degrees. Likewise there are 6400 mils in a circle (17.7 mils per degree). This breaks down even further into approximately 3.5 minutes of angle per Mil. (One Minute of Angle (MOA) is equal to 1" at 100 yds, 2" at 200 yds and so on) That's the important part- 3.5 MOA=1 Mil. "

    MilDot article
  7. Smokin Guns

    Smokin Guns New Member

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    Thanks again Jay!...I'm learnin' through y'all!!!


    BTW, I need some help on Unertl Scopes in the "Whats it Worth" forum...;)
  8. Jay

    Jay New Member

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    I get off work at midnight, but I'll post a link to a gent that sells the older scopes, but I don't know anything about them other than the bare basics.

    Jay
  9. FN_Project90

    FN_Project90 New Member

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    HEHE thought I would get ultra technical and anal, can't remember where I got the picture I used it in a post before though

    Minute of Angle
    Most firearm sighting scopes incorporate windage and elevation adjustments referenced to MOA (minute of angle). Each click of the scope turret is usually 1/4 MOA change and on some scopes 1/8 MOA. Normally, shooters refer to these adjustments as a change of a fraction of an inch at 100 yards rather than the true value of MOA for which they are supposedly calibrated to. The value of inch is a nice easy number to work with and most of us can easily visualize its length and its multiples without the aid of a calculator. Actually the comparison is close enough to not be of practical concern, especially at distances up to a few hundred yards, and the real difference is a mere 0.47 inch at 1000 yards. For serious target shooting and as shooting distances increase the attention to MOA value relative to sight adjustment becomes more essential.

    1 moa, inch grouping @ 100 yards. .5 moa 1/2 inch grouping @ 100 yards. 1 moa equals 10 inch grouping at 1000 yards. .5 moa equals 5 inch grouping at 1000 yards.

    Calculating MOA

    The angle of an arc is expressed in number of degrees. There are 360 degrees of arc to a full circle. Each degree consists of 60 minutes of arc. The distance covered by the measure of arc is relative to the circumference (total distance around the circle) it is contained within. Knowing the radius (distance to center of circle) circumference is easily calculated by using the constant pi . The ratio (represented by pi ) of circumference is constant to diameter (radius x 2) regardless of circle size. The precise value of pi is so far unknown to man but is normally resolved to 3.1416 or 3.141 for our purposes.


    Suppose a circle with a 6 inch radius. Circumference can be calculated as:

    circumference = (radius x 2) x pi
    circumference = (6 x 2) x 3.1416
    circumference = 12 x 3.1416
    circumference = 37.6992 inches

    The distance covered by 1 degree of angle (37.6992 / 360 or, circumference divided by 360 degrees) is 0.1047 inch at 6 inches from center of circle.
    And, 1 minute of angle represents (0.1047 / 60 or, 1 degree divided by 60 minutes) 0.001745 inch at 6 inches from center of circle.

    Knowing what MOA represents allows us to calculate its value to any distance.
    Six inches (the radius of the above example) is 1/600th of 100 yards: (100 yards x 36 inches) / 6 inches = 600
    Therefore, the value of MOA at 100 yards is 1.047 inches (0.001745 x 600 = 1.047)
    At 50 yards 1/2 the 100 yard value; 70% @ 70 yards; twice @ 200 yards; 6 times @ 600 yards; and so on.
    So, the difference between thinking in inches as opposed to MOA is 0.47 inch @ 1000 yards.

    Where group size is expressed in inches the word 'inch' should be spelled. Writing the symbol commonly used to represent the measure of inch (") is not accurate here, and in fact misleading since that symbol also represents 'second of angle' (1/60 of a minute of angle). Therefore, a group of 1 inch would properly be written as '1 inch' not 1". It could also be written as 1' since that symbol (') is used to represent minute of angle but that might be misleading to those thinking in feet.

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    Last edited: Oct 25, 2003
  10. stash247

    stash247 New Member

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    Back to the basics: If that Romy is shooting into 9" at 100 yds, that's 9moa, more or less. During bird season, we call that a pattern, not a group.
    Look at the muzzle, and closely. I will bet the crown is sloppy, or the lands washed out from cleaning from that end. Either one suggests a trip to the gunsmith, either to recrown, or replace, that barrel.
    A .22 target rifle is capable of groups in the 2's, or less, at 100 yds. It could be ammo, but unless this rifle sees nothing but "what's cheap" at Wal Mart, I suspect the problem goes deeper.
    If you are in love with the rifle, think about a barrel; otherwise, think about a gun show.
  11. kaylan1

    kaylan1 New Member

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    I agree with stash247. Thank you Professor FN_Project90 on that enlighting and information class on MOA .You explained it very well and It was easy to understand, evens fer me.I gots the jist of it.

    Can I get College Credit hours for that? I need them.:D
    Last edited: Feb 25, 2004
  12. masterdave

    masterdave New Member

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    moa

    :D M.O.A. is a way of measure . ! moa is one inch ,if a gun shoots 1/2 moa it shoots a one half inch group [thats not always an easy thing to do .where do you live smokinggun ?im new to the forum but i see you question and anser in 22 rimfire and said you dont like snow !! welcome to the club hope to hear from you KEEP EM IN THE BLACK Dave
  13. Smokin Guns

    Smokin Guns New Member

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    Dave, A central Ohio "Buckeye" here...I keep a'tryin...;)
  14. Crpdeth

    Crpdeth Active Member

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