Relationship between 1MOA and 1Inchs in Ballistics Calculator.

Discussion in 'Long Range Hunting & Shooting' started by irish sitka, Jul 31, 2011.

  1. irish sitka

    irish sitka Active Member

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    Jun 19, 2011
    Looking for some info here please.
    I am using 130g Hornday in a Ruger 270.
    The sight I use has 1/4" MOA at 100yds, 4 clicks 1" at 100yds.

    Ballistics Calculator drop down chart:

    .....................Drop.........................Wind
    .....................1 moa......................1. moa
    100yds.........1.2.............................0.0 R
    200yds........-0.0............................-0.0 R
    300yds........-1.6............................-0.3 R
    400yds........-3.4............................-0.4 R

    If I change the heading MOA to Inches obviously the figures change.
    What I am looking for is the connection between the MOA and the Inches.
    Sorry about all the dots! Would not load properly without them!
    Does what I am saying make sense?
    I am sure someone will explain it to me.
    Thanks in advance.
     
  2. RockyMtnMT

    RockyMtnMT Official LRH Sponsor

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    Mar 25, 2007
    I am sure someone will say it better than I, here is my shot at it.

    It has to do with how your scope is set up to adjust. It is probably set up in one of two ways. IPHY or MOA. IPHY= inches per hundred yards. MOA=minute of angle. Look in your scope manual to find out what your click value is and use that in your ballistics calculator. The difference is not very much but will become very noticeable at the longer ranges.

    Steve
     

  3. SBruce

    SBruce Well-Known Member

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    Oct 31, 2009
    Dont know for sure if this is what you're asking for, but 1 moa subtends 1.0472" at 100 yds.

    10 moa (if the scope is accurate) will move the bullet approx 10.5 inches at 100 yds (10.472"). 20 moa is double that.

    If you know that your bullet drops from line of sight 78" at 700 yds, then figuring IPHY is easy. 78 divided by 7 = 11.14 IPHY. Simplified to 11 or 11+ a click on an IPHY scope.

    Figuring the true moa takes another calculation. 78 divided by 7, divided by 1.0472 = 10.64 moa. Simplified to 10.5 or 10.75 marks on a true MOA scope.

    Some programs that I've seen allow you to get the correction in either IPHY or true MOA.

    Your example of 3.4 minutes at 400 yds equates to 3.56 IPHY, or 14.24 inches low at 400yds. (3.4 times 1.0472 = 3.56............3.56" times 4 = 14.24").
     
  4. Browninglover1

    Browninglover1 Well-Known Member

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    Jan 10, 2011
    S Bruce nailed it right on the head. The difference become more noticeable at longer yardages. At 1000 yards for example if you you assumed 1 MOA was 10 inches and dialed in 30 MOA into your scope (to try and bring your point of impact up 300 inches) you would actually move your group by 314.1 inches and miss your intended target by over a foot.