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meaning of MOA?

Discussion in 'Rifle Country' started by Charles W Webb, Nov 15, 2005.

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  1. Charles W Webb

    Charles W Webb Member

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    Well I am wanting to get into long range shooting and such and I have heard the term MOA alot but have never found out its meaning. Any info would be apreciated, thank you.

    Charles
     
  2. Canuck-IL

    Canuck-IL Member

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  3. Domino

    Domino Member

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    If I am not mistaken MOA stands for "minuted of angle"

    This refers to accuracy based on how many inches a gun shoots at the distance of 100 yards.

    If a rifle shoots at 2 MOA it means that it groups 2" at 100 yards.
     
  4. Charles W Webb

    Charles W Webb Member

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    Thank you both for taking the time to answer my post.:cool:
     
  5. rockstar.esq

    rockstar.esq Member

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    Minute of angle.
    Not so common vernacular.
    A degree of angle is further divided into 60 minutes and further 60 seconds. Minute of angle refers to the tangent of the greatest group dispersion divided by the radius (linear distance to said target). By most accounts 1/60th of one degree is considered fine accuracy. The actual dispersion of 1 MOA at 100yds is .96 inches. Most folks assume one inch and tack on another every hundred yards. For example one minute of angle accuracy at 1000 yds would be 10 inches!
     
  6. Hawken50

    Hawken50 Member

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    dosen't it double with every hundred yards?

    1moa @ 100yrds = 1 in
    1moa @ 200yrds = 2 in
    1moa @ 300yrds = 4 in
    1moa @ 400yrds = 8 in
    1moa @ 500yrds = 16 in

    i have been wrong before...once.
     
  7. USSR

    USSR Member

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    MOA - Minute of Angle.

    1MOA = 1.047" @ 100 yards
    1MOA = 2.094" @ 200 yards
    etc.

    1MOA is typically rounded off to 1 inch. Long range competitors and snipers make scope adjustments/corrections in MOA - not clicks. If you have a typical scope with 1/4" adjustments and you are shooting 3" low at 100 yards, your spotter will tell you to come up 3MOA - not 12 clicks. Hope that helps.

    Don
     
  8. Swampy

    Swampy Member

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    A true geometric "Minute of Angle" is 1.047" at 100 yds, 2.094" at 200 yds.... etc....

    A SHOOTERS "Minute of Angle" is 1.00" at 100, 2.00 at 200..... and etc...

    Now it's twice.....:p
    The progression of MOA is geometric, not exponential.....

    1moa @ 100yrds = 1 in
    1moa @ 200yrds = 2 in
    1moa @ 300yrds = 3 in
    1moa @ 400yrds = 4 in
    1moa @ 500yrds = 5 in

    Best to all,
    Swampy

    Garands forever
     
  9. GoRon

    GoRon Member

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    Here is a great post from TFL that I copied for future reference.

     
  10. Rockstar

    Rockstar member

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    Well, rock, at least your name was on-the-money! :)
     
  11. benEzra

    benEzra Moderator Emeritus

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    One thing that's confusing is that in most technical fields, "minutes of angle" are usually called arcminutes. One arcminute (e.g., 1 MOA) is 1/60 of a degree. In astronomy, you'll also see arcseconds, 1 arcsecond being 1/60 of an arcminute.

    An arcminute/MOA is a TINY angle. To put it in perspective, the earth rotates one arcminute/MOA every 4 seconds...
     
  12. Hawken50

    Hawken50 Member

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    awww nuts, there goes my track record of near perfection.
     
  13. Bwana John

    Bwana John Member

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    Actually MOA measures the angle that the group subtends, it is NOT a linear measurment.:banghead:
    This method of quantifying group size only "works" for very small angles.:cuss:
    The math is actually much easier if radians, instead of degrees are used.:evil:

    A more accurate method might be: 2 X arctan (1/2 group size / distance to target). This method would relate linear group size to the change in angle the barrel experances, without the problems of compairing radius to circumference.

    AND just because a rifle shoots 1 inch groups at 100 meters does NOT mean you will shoot 10 inch groups with it at 1000 meters.:scrutiny:
     
  14. USSR

    USSR Member

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    Ahhh, you noticed that too.:D

    Don
     
  15. Zak Smith

    Zak Smith Moderator Emeritus

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    For any rifle type accuracy measurements, the error between the linear distance and circumferential distance is about 7 / 1,000,000,000. In other words.. WAY past the number of significant figures you can measure in group size anyway. In summary, for rifle accuracy, use 1.047 or 1.0472" per 100 yards.

    -z
     
  16. Swampy

    Swampy Member

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    Granted..... but up until this point I don't think that's what the issue was.... It WAS just about defining what a shooters MOA was, not what a rifle was capable of....

    Now maybe's the time to switch tracks??? :p

    Just my opinion,
    Swampy

    garands forever
     
  17. ScopedOut

    ScopedOut Member

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    So a rifle capable of, say, 3/4 MOA at 100m is not necessarily capable of 3/4MOA at 900m? I'm guessing that factors both intrinsic to the rifle (bedding, spin rate, muzzle velocity, load consistency), and extrinsic (wind, humidity) play a role in widening the cone of precision?

    Here's my chance to learn. Any takers?

     
  18. Swampy

    Swampy Member

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    True.....

    Once the bullet leaves the muzzle it's "on it's own" so to speak and each bullets individual idosyncrasies and imperfections come into play with where it ends up at the terminal point of the trajectory..... i.e. dispersion from the ideal. :(

    It's generally said of a bullet-load-rifle combo that, "If it's gonna' shoot 1 MOA at 600 yds (the size of the MR target X-ring is 6" diameter) it'd better shoot 1/2 MOA at 100 yards".

    No hard rule that for certain... but just a common saying among Highpower shooters. There is some truth to it for sure.......

    Best regards,
    Swampy

    Garands forever
     
  19. 30Cal

    30Cal Member

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    Velocity, drop and windage aren't a linear function of range (there's no straight line in a bullet's trajectory). Makes sense that accuracy isn't either.
     
  20. Molon Labe

    Molon Labe Member

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    O.K., dumb question time:

    If a firearms manufacturer says one of their rifles has an inherent accuracy of 1 MOA at 100 yards, what exactly does this mean?

    I can think of two definitions:

    1. The maximum error is 1 MOA. This means the point-of-impact (POI) will have a maximum error of 1.047" from the point-of-aim (POA) at 100 yards (error = POI - POA). If we use this definition, then a group of shots will have a maximum radius of 1.047", which means the maximum diameter of the group will be 2.094".

    2. The maximum diameter of the group is 1.047". This means the worse error (error = POI - POA) is 0.5235".

    So which is it? I assume it's #2.
     
  21. Zak Smith

    Zak Smith Moderator Emeritus

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    There is usually no concept of "error" of POA away from POI, the logic being that you can adjust the point of aim to the center of the group.

    Group size is normally the maximum center to center distance for a 3, 5, 10, etc, shot group. In practice, it is easiest to measure by measuring the maximum outside to outside distance and subtacting one bullet diameter.

    -z
     
  22. USSR

    USSR Member

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    Molon,

    First, manufacturers don't use the term "inherent accuracy". Only guys on website forums who believe certain cartridges possess mythical powers, and any rifle you chamber in that cartridge will be accurate use these terms.;) You are correct in your assumption that it is your #2 definition, although the .047" is usually dropped. The number of rounds fired to constitute a group are specified (usually 3 or 5), and although the type of ammo used is usually not specified, it is assumed to be match ammo such as Federal Gold Medal Match. The really top gunsmiths will guarantee the rifles they build to deliver 0.5" groups at 100 yards.

    Don
     
  23. Molon Labe

    Molon Labe Member

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    I guess I was referring to the accuracy of a rifle that is mounted in a vice. In other words, the inherent, "mechanical" accuracy of a rifle + ammo combination.
     
  24. USSR

    USSR Member

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    Molon,

    Nobody shoots their rifle in a "vise".

    Don
     
  25. Medusa

    Medusa Member

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    Well, the coefficient of friction is proportional to the speed, at high speed it's proportional to the velocity's square, at lower speed to the velocity itself. So the trajectory of flight has a shape of ballistic curve instead of perfect arc, besides, other factors that affect the projectile's flight are gyroscopic effect, then the lift created by the spin (total blackout on the effect's name :cuss: ), drag that depends on bullet's shape (whether the airflow is laminar or turbulent at the boattail), then of course the Coriolis effect, differences in air density (by pressure and temperature) over the flightpath, fluctuating gradient vectors of pressure and temperature. Hmm did I miss something? surely did :banghead: Did I mentioned wobbling hands and breathing at the wrong time?
     
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