how to set up balistic plex drop to 45-70 rainbow?

Discussion in 'Long Range Scopes and Other Optics' started by 01mikep, Jan 4, 2009.

  1. 01mikep

    01mikep New Member

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    Jan 4, 2009
    This is probably simple for most of you on here but kinda confusing to me. I think I have been working in the wrong direction.

    The cross hair is zero
    first drop down is 1.5
    second drop down is 4.5
    third drop down is 7.6
    fourth drop down is 11

    this is in inches @ 100 yards

    Burris gives a drop chart for 100 to 500 yards and 200 to 600 yards but
    the 45-70 obviously does not match up to those yardages. How can I match
    the drop to the 45-70's more rainbow like bullet drop. I know the drop of my loads, just not how to compare it to the drops on the scope.

    Thanks all.
     
  2. KRP

    KRP Well-Known Member

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    591
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    Dec 25, 2007
    Divide the drop in inches by the yardage in hundreds to see where each hash will zero. Then just work your way down you drop chart for all the hash marks.

    For example if you have 2.25" drop at 150 yards, 2.25(drop in inches)/1.5(yardage in hundreds)=1.5(IPHY of first hash) so that is where the first hash is zeroed.

    With a variable power SFP scope you can change the magnification setting and change the subtensions of the reticle also. Cut the magnification in half and the subtensions double.

    If you want to do it the easy way you could post your drop figures here and someone can run them through Exbal and give you the numbers.
     

  3. 01mikep

    01mikep New Member

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    Jan 4, 2009
    So when I divide my bullet drop by the yardage in hundredths, that is my holdover @100 yards. My question now is if I zero at something other than 100 yards how can I apply the data that I have for 100 yards. If I zero at 100 yards with this rifle, I use up all the drop hashes by 225 yards. I would like to stretch it to 325 or 350 if possible. Is there a better scope to use than the burris Fullfield II 2x7 with the ballistic plex on a 45-70 marlin w/18 in barrel. I'm just tired of being limited so much by guessing holdover (not accurate).
     
  4. KRP

    KRP Well-Known Member

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    Dec 25, 2007
    The math is the same no matter what yardage you choose to zero at. Zero at 150 or 200 or whatever you choose and then work down the chart figuring where each hash is zeroed from there. Some sort of Mil/MOA reticle may be of more use, you can have custom ballistic reticles installed in some scopes, or you could go to a scope with turrets and dial the corrections. Like I said you can dial the power down on the scope and increase the subtensions also so you can figure the hash zeroes at different power to shoot different distances.
     
  5. Tyler Kemp

    Tyler Kemp SPONSOR

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    Aug 10, 2006
    Just times the inches that the scope reticle dimensions are at 100 by MOA (1.??) and then you have the drops in MOA. Just compare that to your ballistics chart and go to town!
     
  6. woods

    woods Well-Known Member

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    Jun 4, 2006
    Hey mike

    Taking a typical 45-70 shooting a 300 gr bullet at a typical 2200 fps with a typical ballistic coefficient of .200 would have the following trajectory when zeroed at 100 yards:

    100 yds - 0"
    150 yds - 3"
    200 yds - 9"
    250 yds - 19"
    300 yds - 33.6"

    So the reticle will subtend the following at the following yardages when zeroed at 100 yards:

    crosshairs - 100 yds - 0"
    1st line down - 150 yds - 2.25" (1.5x1.5=2.25")
    2nd line down - 200 yds - 9" (4.5x2=9")
    3rd line down - 250 yds - 19" (7.6x2.5=19"
    4th line down - 300 yds - 33" (11x3=33")

    Dude, just zero at 100 yards and the reticle will match that trajectory exactly for every 50 yards out to 300 yards. They were made for each other!

    What's the problem?