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Thread: Balliastic Software and the 20moa rail

  1. #1
    Join Date
    Jun 2015
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    St Louis Bench Rest Club
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    32

    Balliastic Software and the 20moa rail

    I'm having a hard time wrapping my head around how my ballistic software ("Shooter") can predict that I need U5.6 for my 308 shooting 168grain Sierra @ 600 yards when it doesn't ask if the rail the scope is mounted on is flat or if it has a 20 MOA tilt. If you could enlighten me I would appreciate it. Thanks, Bill.

  2. #2
    Join Date
    Dec 2003
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    washington.........STATE that is.
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    "mounted flat" just means that the "tilt" is inside your scope

    A 20moa rail puts some of this "tilt" outside but doesn't change the fact that all the program needs is the separation (distance) from boreline to centerline of scope.

    help?

  3. #3
    Join Date
    Jul 2009
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    Northshore
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    Did your program ask for your zero. If you zero your scope at 100 then 100 yard zero is just that, no matter what rail. You will just have more elevation from one or the other.

  4. #4
    Join Date
    Jun 2015
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    St Louis Bench Rest Club
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    OK that makes sense. But I'm using a Schmidt & Bender 12-50x56 PM II/P which has 75MOA elevation. The SB PM has an elevation turret that has five rotations. Each rotation then means I have 15 minutes of elevation. If I am bore sighted at 100 yards and I'm starting the fourth rotation that means that I have already used up 45MOA even with the 20 MOA rail. Something just looks wrong to me. If I had not started with the 20 MOA rail it seems I would now have used up 65 of the 75 MOA that I had to work with. What do you think?

  5. #5
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    Did you put your rail on backwards? The low end goes to the front.

  6. #6
    Join Date
    Mar 2013
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    Nelson New Zealand
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    In theory if the barrel is set up nicely in the action & they are in the stock nicely & your have good rings a zero rail should have you sighted in at 100 at around the middle of the scope elevation adjustment, 37.5 moa, if you used a 20 moa rail installed correctly you should be 20 moa lower, so 17.5 moa, so 57.5 moa up.

    With a canted rail the scopes objective is pointing down & the eye piece pointing up compared to the centre line of the bore

  7. #7
    Join Date
    Jun 2012
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    West central NH
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    Put another way, the purpose of the 20 MOA rail is to give you 20 more MOA of elevation adjustment than you'd have if your scope was mounted flat, or parallel to the bore of the rifle. It is especially helpful with a one inch tube, which on average will have less elevation adjustment than a 30 or 36mm tube.

  8. #8
    Join Date
    Jun 2015
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    St Louis Bench Rest Club
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    I'm going to fall back until I get it zeroed. At this time I'm pretty sure something is crossed up. I agree the 20 MOA rail should put me in the neighborhood of 17 to 20 MOA when zeroed at 100 yards. I'll post what I find. Half of the fun is figuring out stuff like this. Thanks for the help. Bill.

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