How is this trajectory possible?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by twoftagl, Dec 24, 2012.

  1. twoftagl

    twoftagl Well-Known Member

    Messages:
    82
    Joined:
    Apr 21, 2012
    I set out yesterday to find out my actual drops, just to compare and fine-tune the profile in EXBAL. After measuring the drops, I can't find a reasonable profile. The measured drops are so far off I must be missing something, I can't figure out how to get a 23.5" drop at 400yards and 73.5" at 600 on either shooter or Exbal.

    300 wm (winchester load)
    180grain bc=.438
    mv2960 published (I was showing avg of 3028)
    55 degrees / 300 feet / 23% / sea level pressure 30.05
    200 yard zero / sight-in conditions same as above
    sight height 1.925

    measured drop:
    400yd: 23.5" 5-shot group
    600yd: 73.5" 4-shot group (one flyer excluded)


    In order to get a profile to match in the given conditions, the closest I can come in EXBAL is a bc of 1.25 and mv of 2510 fps!!???!!?? That's rediculous. The 400 yard drop is about 4" lower than what it should be shooting, and the 600 yard drop is about 6" lower.

    I must be missing something completely here. Only thing I can think of is when I went from 400 to 600 I neglected to set my parallax. Doesn't seem like parallax was an issue though, cause there were four within a 5.8" vertical spread which is about the moa I usually get with that load. The fifth shot was so far low that I had to rule it out. Only setting I changed on the scope was the windage, just to keep it on the cardboard.

    Any ideas? The actual drops don't even add up to the dopes I usually use, 19 clicks (1/4 moa) at 400 and 42 at 600.

    Chris
     
  2. farout

    farout Well-Known Member

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    Joined:
    Nov 21, 2011
    twoftagl,

    I ran the number through the Berger bullet drop calculator.

    Using a 200 yard zero the drops were:
    400 yards 19.0"
    600 yards 67.24"

    Using a 100 yard zero the drops were:
    400 yards 24.02"
    600 yards 74.76"

    Using the 100 yard zero the number are very close to yours. Maybe you are zeroed at 100 yards?
     
  3. Joe King

    Joe King Well-Known Member

    Messages:
    1,390
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    Apr 29, 2012
    Can you not use G7 BC's? What make you certain that your MV's are what they are, unless you have a very very good ie expensive chrony I wouldn't take what it says to heart. drop your MV on exbal til it matches up with what your actual trajectory is.
     
  4. twoftagl

    twoftagl Well-Known Member

    Messages:
    82
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    Apr 21, 2012
    Jeez that's scary!! Those numbers are right-on!

    I've been using this zero for a while now...had to re-set the turrets when going to 200. Yesterday when I re-verified it was very close (ended up making a 1-click adjustment). I would've had to do the same thing twice. Those numbers are so darned close, though...there has to be something there...hmmmmmm

    Chris