MOA/ Click type question

Discussion in 'General Discussion' started by jmason, Jun 10, 2009.

  1. jmason

    jmason Well-Known Member

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    For some reason my brain isn't cooperating with me today. I went out this morning to do a trajectory validation and check my spin drift but it was so foggy I couldn't see past 100 yds. So I decided to try to find out the actual click value of my scope. Didn't want to waste the trip and had to go to work.

    Here is the info:

    Distance to target 107 yards
    advertised click value of scope 1/4 MOA per click

    I shot a 3 shot group at my zero dot then I dailed 28 MOA up and shot 3 more.

    From center to center (top group to bottom group) I have 30 9/16"

    What the heck is my actual click value?
     
  2. 406pat

    406pat Well-Known Member

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    I'll take a crack at it.

    At 107 yards, 1 MOA=1.07"

    you have 30 9/16" or 30.5625"

    (Sorry, I'm an engineer by trade and prefer to work in decimals)

    30.5625"/1.07"=28.5631 MOA

    If you dialed up 28 MOA that means you went up 112 clicks on your scope (28 MOA X 4 clicks per MOA)

    If you actually got 28.5631 MOA that means that each click was worth .255 MOA

    By this reasoning The actual MOA/click value is .005 MOA greater than advertised.

    If this is correct than at 1000 yards each click would give an additional .05" of elevation above the 2.5" that 1/4 MOA would be.

    This is also assuming that MOA means 1" at 100 yards. I know there's some other definitions out there but that's another issue.

    I hope someone double checks me on this.
     

  3. AJ Peacock

    AJ Peacock Well-Known Member

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    406Pat, pretty close.

    You needed to use 1.047" for MOA at 100yds, which gives 1.12029"/moa at 107yds

    28moa*1.12029=31.37

    Spread of group is 30.5625" for a difference of .81" or .72moa difference.

    If the gun and shooter were perfect, then the scope would be off by .72MOA, however I don't know how large the groups are. Unless the gun and shooter are both worldclass (less than 1/4moa group sizes), then I would trust the scope.

    AJ

    ps: Hopefully, someone will double check my calcs.
     
  4. WildcatB

    WildcatB Well-Known Member

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    1" at 100 yards is referred to as "Shooters MOA".

    True MOA (Minute of Angle) is 1.047" (rounded) at 100 yards. To get this number take the tangent of 1 min (or .0166666 degrees) and multiply that by the distance in inches.

    At 107 yards a true MOA is 1.121" (rounded) at 100 yards

    Some scopes dial Shooter's MOA others true MOA.

    It looks like yours is Shooters MOA. The .005 difference per click in advertised value that 406Pat got using a Shooter's MOA is very close. The difference is most likely due to group variance and measuring error.

    Shoot more groups, re-calc, and see what you get next time.


    Paul
     
  5. jmason

    jmason Well-Known Member

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    Defiantly not the case. However If I understand what your saying. Then there's not enough error for me to worry about, right? The bottom group was .75MOA and the top one was .2 (probably the best group I ever shot oddly enough). The gun is a 270 win.

    So what does being off .72MOA make my click value, .18846? (.72x1.047=.75384/4=.18846)

    What ever I get here for error is likely me. Just curious what you guys come up with.
     
  6. AJ Peacock

    AJ Peacock Well-Known Member

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    It would be (error)/(adjustment) or .72/28 or 2.571% error. Assuming you had shot it perfectly, that would make each click 1.047/4*1.02571=.2685moa.

    However, with only a single test, it is likely that your group center isn't actually the center of a larger sample size. If the center of the second group was actually at the top of the group, then your error would be reduced by .75/2 = .375, leaving an error of .72-.375 = .355. If the smaller group center was at the edge, that could reduce your error another .1moa.

    I would personally trust the scope, unless you can duplicate the measurement several more times. My guess is that your scope is very close (close enough to ignore).

    AJ
     
    Last edited: Jun 10, 2009
  7. jmason

    jmason Well-Known Member

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    Thanks AJ. Thats what I was lookin' to hear.