Ballistics question? 20 MOA base vs. 0 MOA base

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by bowhunthard, Aug 16, 2010.

  1. bowhunthard

    bowhunthard Well-Known Member

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    I was wondering if anyone knows the answer to this question: will there be an actual physical difference in a drop chart for a 20 MOA base vs. a 0 MOA base?

    I realize velocity, etc. would stay the same, but will the bullet from one of the bases impact higher than the other at a set range other than the zero? If both bases were zeroed @ the same range? Or does the 20 MOA only allow the scope zero to be set with less clicks for an extended range?

    I'm just trying to see if buying a 20 MOA rail would be worth it for me, ballistically that is.

    I think I over-thought this, and now I'm confusing myself lol... Will I be able to use my ballistics program accurately with a 20 MOA base?

    Thanks.
     
  2. NomadPilot

    NomadPilot Well-Known Member

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    No.
    Yep, that one.
    Yes.
     

  3. X3MHunter

    X3MHunter Well-Known Member

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    All the 20 MOA base will do is allow you to shoot further because you will have 20 MOA more of usable elevation in your scope, other than that, everything else is the same.
     
  4. bowhunthard

    bowhunthard Well-Known Member

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    Thanks so much. That's what I originally thought, but I thought about it so much I guess I over analyzed and ended up thinking the opposite lol.

    Thanks again.
     
  5. zupatun

    zupatun Well-Known Member

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    Someone correct me if I'm wrong--here's how I think about it...

    Normally, your scope would be zeroed in (if bases and rings are machined and fitted true and level) close to the center of the range of your scope adjustment...so you can dial "up" for only about half the whole range of your scope, if needed, to compensate for your drops.


    What the 20 MOA base does is tilt your scope. Now you have to re-adjust your scope "down" so you are lined up with your zero point. You "new" starting point for zero is now in the lower half of your scope adjustment "down" ~20 MOA, so you now have that 20MOA and the rest of the other half of the range of your scope adjustment to "dial up" for your drops.

     
  6. Mikecr

    Mikecr Well-Known Member

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    Perfect explanation Matt!
     
  7. barthmonster

    barthmonster Well-Known Member

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    Yeah that's right, except now my scope doesn't go low enough to zero. Is that why people use a 30mm tube scope and not a 1" tube a lot ? I'm shooting 8.5" high (.308) at 100 Yards and can't lower it with the scope. Somethings gotta give...
     
  8. Autorotate

    Autorotate Well-Known Member

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    No.

    No. Example, if you zero two identical rifles at 200 yards, but one has a zero MOA base, and the other has a 40 MOA base, and then shoot at a 1000 yard target with both rifles, the bullet drop from both rifles will be identical.

    No, the adjustment from your zero range to the target at extended range will be the same regardless of the amount of taper on your scope base.

    You need to evaluate a couple factors to see if a 20 MOA is a good fit for you. First, how much total elevation travel does your rifle optic posses? What is your minimum intended zero range? What is your maximum intended range for the rifle?

    Yes, all ballistic programs will function perfectly no matter the base you put on the rifle, provided the ballistic solution doesn't exceed the elevation/windage adjustment of the rifle.

    Fire back your next set of questions..after you answer the ones above....make sure this get's cleared up!

    The main purpose behind a canted base is to permit elevation adjustment of your optic at extended ranges. With a 0 MOA base, your optic is roughly aligned (should be depending on the profile of your receiver) with the bore centerline. If your optic has 50 MOA total of elevation travel, then with a 0 MOA base, the elevation adjustment is probably close to center with a 100 yard zero, leaving you 25 MOA adjustment up and down.

    Long range hunters would rather use that 25 MOA worth of adjustment towards long range elevation travel...so they mount 5, 10, 15, 20 etc MOA bases to their rifles to extend the useful elevation range of their scope.

    In the example above, and if the optic was centered with the bore centerline on a 0 MOA base.....if the 50 MOA optic was mounted on a 10 MOA base, the optic would have 35 MOA travel "up" (bullet path movement), and 15 MOA "down".

    In the same example, if mounted on a 20 MOA base, it would now have 45 MOA travel "up", and 5 MOA "down". This might be considered marginal on the "down" adjustment remaining, to ensure the capability to zero at closer (100-200 yd) ranges.

    Another factor to consider, especially with factory actions, is the profile of the action can contain significant alignment errors (both windage and elevation, but will focus on elevation for this post), that can "rob" your optic of some travel (sometimes as much as 5-7 MOA).

    Additionally, some optics, have been known to "walk" or introduce a windage error at the extreme limits (top or bottom) of their elevation travel range...it's thought best to try a place the elevation adjustment towards the center of it's operating range, to minimize the chance/effect of this, no matter the quality of the optic.

    Hope this helps! Good shooting!gun)