Tall Target Test

Discussion in 'ELR, Ballistics & Bullets Board' started by chromatica, Aug 26, 2017.

  1. chromatica

    chromatica

    Joined:
    Jun 12, 2013
    Messages:
    81
    Tall Target Test



    Date: 7/28/17

    Location: Escondido Fish & Game



    Ballistics post:



    Bryan has been urging all of us to conduct a tall target test to calibrate our optics and to do this before we begin any long distance work. I decided to give my rig a shakedown before heading out to the LRP world. My rifle is a custom .260 LRP built on a Savage platform. It is equipped with a Steiner 4-12x50 military scope so I expected it to do a good job of tracking.



    In order to make a Tall Target, I picked up some foam poster board from a big box office supply store. I created two 36-inch vertical scales separated by about 14 inches. I put tick marks 5 inches apart, knowing I would use a yardstick to make precise measurements after the fact.



    While I was making the target, I read about a leveling jig on one of the forums, Brownells (part # 289-100-000WB) so I ordered one. When it arrived I set up to align the crosshairs of my scope and adjust the scope level properly. The aluminum jig has two vblocks that ride a slotted bar – one sits on the scope bell and the other sits right on the barrel. There is a bubble level across the top of the larger vblock to let you know when the line going from the center of the scope down through the axis of your barrel is exactly plumb. I adjusted the rifle on its bipod until the bubble level was centered. Then I hung a plumb bob at the other end of the house and rotated the scope in its rings until the vertical crosshairs aligned with the plumb bob. Bingo, all set for the range!



    I set up with a buddy at one of the local private ranges. There was a mild breeze I estimated to be 2-5 mph. We tried using a plumb bob to hang the target so the scale would be exactly plumb, but the light breezes deflected the bob and made it impossible to take a reading. We shifted to using a carpenter’s level. This turned out to be the right answer. I had previously zeroed the scope, but because of the previous scope leveling adjustments, I needed to recheck my zero. I adjusted the elevation using the bull on the tall target. There was a mild breeze and I decided to zero horizontally using the windage turret instead of trying to hold off for changing wind conditions.



    My helper spotted for me as I began the upward steps on the left-hand scale of the target. I added increments of 2.5 milRads to my starting elevation, placing four shots at each of the intervals. Beginning at 0.8 milRads I increased the elevation to 3.3, 5.8, 8.3, and finally 10.8 milRads. After allowing the barrel to cool, I started downward on the right hand scale of the target to see if there were any signs of hysteresis. I noticed that my groups opened up on the way down. My helper had found some other things to do during the break and so I had more work to do to count the rounds and keep records. I experienced several light strikes (http://forum.accurateshooter.com/threads/problem-with-light-strikes.3931634/) ; this also interrupted my concentration. In general though, I was pleased that the scope tracked vertically and that quick measurements with a yardstick showed that the elevation intervals were right on the money. I have renewed confidence in my optics and the entire shooting platform.



    When I got home, I averaged the z measurement using a spreadsheet. Here are the results:



    Moving Upward


    Elev Expected Avg Measurement

    2.5 9 in 9.3 in

    5.0 18 18.225

    7.5 27 26.9

    10.0 36 36.06

    Moving downward:

    <yet do do>


    Here is a picture of my Tall Target:





    Tall Target.jpg
     
    IdahoSharpshooter likes this.
  2. boltfluter

    boltfluter Gold $$ Contributor

    Joined:
    Jan 3, 2012
    Messages:
    1,788
    Looks like you have a winner there. Always nice to know that your optics are tracking like they should. :):cool:

    Paul

    www.boltfluting.com
     

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