Chrony/Ballistics Software Discrepancies

Discussion in 'Reloading' started by texastrophy, Sep 23, 2010.

  1. texastrophy

    texastrophy Well-Known Member

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    My chrony records 2980fps. I have to manipulate the velocity to 2750fps in two different ballistics software programs to duplicate the actual field results in bullet drop. The load I'm using should more accurately reflect the chrony results so why is the ballistics software needing to be tweeked so much to accurately reflect my bullet drop? I'm using a G1 BC for a Berger FB bullet and all the climate factors are up to the minute.
     
  2. boomtube

    boomtube Well-Known Member

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    Your experience is why I dropped most efforts to use computers for ballistics, internal and external, years ago. As with "gobal warming", if we have to manlipute the program data to get the results to conform, what the he77 good is it? That ain't science, it's kidding ourselves!
     

  3. RockyMtnMT

    RockyMtnMT Official LRH Sponsor

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    This is a great subject, as there are so many variables that can cause the need for tweaking the program.

    How far are you shooting? Have you tried a different chrony? Is your scope height measured correctly? Have you looked up the current bc listing for the bullet that you are using?

    I guess what I am saying is that it may be something other than your chrony. Try adjusting the bc value to get the drops to match, if you have not done this.

    Good luck

    Steve
     
  4. bigngreen

    bigngreen Well-Known Member

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    What programs are you using? The most common issue is data entry, most programs are very good and better IMO than most crony's these days. If you post your data others can check it, sometimes you can miss the simplest things.
    Also have you checked the calibration of you optic?
     
  5. texastrophy

    texastrophy Well-Known Member

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    I'm using Ballistic v.3.2.8 for iphone and the Berger Ballistic program. I've measured scope height accurately, entered in the BC according to the manufacturer and am shooting at 100 yds. with my Chrony at 15 ft. from the muzzle. All the climate data and bullet data is correct. Both programs come up with very close to the same information.
     
  6. bigngreen

    bigngreen Well-Known Member

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    I've found the Berger program very good if you deal with the environmental data correctly. Have you checked you scope adjustment, it is critical to check. What ranges are you verifying data at?
     
  7. kiwi3006

    kiwi3006 Well-Known Member

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    The only thing I can think of is that you are adding both the station pressure AND altitude. If your Kestrel(or whatever) is giving the actual pressure at your location then set the altitude to zero.
    You might already be doing this, but since you haven't stated what the atmospherics are we don't know.
    Can you post all your data, actual drops at ranges and atmospheric data.

    Stu.
     
  8. texastrophy

    texastrophy Well-Known Member

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    The actual field results show 4.78 inches @ 100 yds and 6.14 inches @ 200 yds with the rifle sighted in at 300 yds. Sorry for the double image post. I didn't know how to remove it once it was uploaded.

    [​IMG][​IMG]
     
  9. kiwi3006

    kiwi3006 Well-Known Member

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    Running your data through AlBal I got the same results as you. It seems very strange that your chronograph is +200 fps out but it islooking that way from your data.
    Do you have access to another chrongraph? What is your load for that round(powder weight, primer etc) barrel length

    Stu.
     
  10. bigngreen

    bigngreen Well-Known Member

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    Have you check the ranges your shooting at with a range finder? I know my range is set up all out of wack and it was giving me fits till I checked it all.

    There is not a change that you can make big enough to make it work, as far as I can tell other than dropping your velocity way down or changing you zero to 330 ish. You really need to shoot past your zero point to get a better idea of what your actual drops are. You lobe one out to 500 or 600yrds and it will tell you right quick what is going on.

    I have a real problem getting a true zero at a specific range, when I'm sighting in I tense up or something stupid and when I run it out there I'm always low so I have to fart around and shoot a few at various ranges then dial to zero and shoot, I do this a few times and stay loose and in the end I end up with a zero high that reflects what I shoot when I shoot a cold bore shot at a LR target, just something to ponder.
     
  11. Forester

    Forester Well-Known Member

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    Does the Chrono give good data with other rifles of similar size/muzzle blast?

    Looks a lot like Chrono error to me. I usually use a chrono to get me close but rely on measured drops at multiple distances as far out as possible to finalize any data I plan to use in the field.
     
  12. anithacbs101

    anithacbs101 New Member

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    I have to manipulate the velocity to 2750fps in two different ... The most common issue is data entry, most programs are very good typing speed is must.<a href="http://www.formfillingprojects.info/category/online-data-entry/"></a>.gun)
     
  13. Mikecr

    Mikecr Well-Known Member

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    It's not a software issue. The ballistic solution is right.
    I would suspect the ranges.

    If your zero was actually ~325yds, both 100/200 POIs would match.
     
  14. rscott5028

    rscott5028 Well-Known Member

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    +1 to all of the above

    ...including, very likely additive/stacking errors...

    - scope height
    - velocity (including SD)
    - ranges
    - measuring exact zero POI (including group size and sampling errors)
    - correolis
    - spin drift