How do you true up your data?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by bdpayne2000, May 31, 2014.

  1. bdpayne2000

    bdpayne2000 Well-Known Member

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    Relatively new at this long range game and was wondering how you true up your data. Read an article by Todd Hodnett and he recommended that you true your data with targets that are within 20% of the transonic range of the load. For example if that range is 800 then that is where you should shoot and true at that point and not a shorter distance. Do you fool with BC's or just adjust velocity?

    Thanks, Brian.
     
  2. Mikecr

    Mikecr Well-Known Member

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    You should measure your muzzle velocity, and if your BC needs adjusting, do just that.
    Don't overlook air density parameters.
     

  3. MMERSS

    MMERSS Well-Known Member

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    Buy Litz's book Accuracy and Precision for Long Range Shooting. There is more to merely adjusting velocity and/or BC to fully true a ballistics solution (tracking, actual click value, etc.). This book goes into great detail on all aspects of what you may be asking and assuredly more. This book is well worth the money and the reading.
     
  4. Chase Curtis

    Chase Curtis Official LRH Sponsor

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    In all honesty... I think this can get too complicated when there is no need..

    I shoot clay pigeons at 600-1000 yards and get real world data and adjust accordingly. Adjust BC or velocity... Don't confuse yourself with the facts. gun)
     
  5. Mikecr

    Mikecr Well-Known Member

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    It gets 'complicated when you walk a mile or two from your truck with a shooting system, and suddenly you spot a clay pigeon at a random distance down in the valley. You range it at ~730yds, a little wind on your face, 5 deg slope, set your gun down onto it's bipod, look up your numbers, dial the scope, level, and take the pigeon, when it stands up again, with one cold bore shot. That's all you get, and if 'simple' for you, because you actually did a little work up front, it's enough for ~80%(C) kill percentage.
     
  6. angus-5024

    angus-5024 Well-Known Member

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  7. Mikecr

    Mikecr Well-Known Member

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    Guess it depends on your standard of 'things'...

    Given exposed killzone for a groundhog(for example), and a little better than 1/2moa system(which is a whole bunch of 'things'), 600yds is challenging enough. No need to delude yourself over random ranges near 1kyd+..

    You don't adjust muzzle velocity to compensate for an error in BC. Muzzle velocity does not change with air density,, effective BC does.
    Measure muzzle velocity and enter what you measure.
    Measure your scope adjustments and enter them.
    Measure distance to several range targets.
    Measure or obtain air density parameters and enter them.
    Enter BC until it's right with results for conditions. AND NOW THAT'S KNOWN.