Ballistics isn't the math the math?

Discussion in 'Long Range Hunting & Shooting' started by Terry Scott, Feb 11, 2012.

  1. Terry Scott

    Terry Scott Well-Known Member

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    Today at the range, shooting @ 960 yds I checked my bullet calcs and hit the gong dead center. After coming home, and looking at 3 different ballistic programs that use all the variables to calc drop, I came up with three different answers, that were as much as 1.5 moa apart.... Isn't the math the math?
    I rechecked my solutions all the variables were the same...but the answers seem to start changing at about 600 yds...
     
  2. SBruce

    SBruce Well-Known Member

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    I've noticed the same thing, although not quite that big of a difference.

    I've got two versions of the Exbal program, and the PDA version has to have 1/2" HG less pressure to give identical results as the PC version. I read somewhere that it was due to different atmospheric models used. Also, I've got the Sierra software, and it doesn't exactly match the Exbal outputs.

    Everything was input exactly the same and Sierra gives 6" more drop at 1000 and 3" more drift.??

    Perhaps they use different drag models also.?
     

  3. joseph

    joseph Well-Known Member

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  4. Autorotate

    Autorotate Well-Known Member

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    IMHO--I don't have the science to back this up, but it's my conclusion on my personal experiences....that each rifle has a unique BC due to variances in stability and groove/bore signature the rifle's barrel imparts on the bullet. So your results in the field vs the computed by your ballistic solution CAN vary (and very likely will).

    Have you "track checked" your rifle scope yet? You may find that more/less elevation is being applied to your reticle than is indicated by your turrent.

    A yard stick at 100 yds, with the rifle locked into a vice, and then manipulate the elevation turrent to the 960 yd solution, and see if your scope is applying the assumed solution.

    If you hang the yard stick level with a plumb line, you can verify your optic isn't introducing any "windage" into your elevation only solution as well, during this same range session.

    Good shooting!gun)
     
  5. 4xforfun

    4xforfun Well-Known Member

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    I agree....every gun lets em fly different. BUT....I think that the programs should all spit out the same numbers.

    I think we should get the government involved to find a solution and fix the problem. Obama's team will ger-R-done!!

    TAKE AWAY OUR GUNS...PROBLEM SOLVED!!

    Sorry...couldn't resist.:D
     
  6. rscott5028

    rscott5028 Well-Known Member

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    You're right. Math is math.

    But, there are a number of reasons why different software may give different solutions especially as you extend your distance.

    - different assumptions (e.g. atmospheric conditions, scope height, inches or true MOA, corriolis, spin drift)
    - rounding error (depending on how the program was written)
    - software bugs (there are sometimes bugs in the application, libraries, or even a chipset)
    - sloppiness (did the programmer ever think you'd shoot past 1000 yds?)
    - stacking error (a little bit here and there adds up at longer ranges)

    Similarly, shooting results may deviate from software predictions for a variety of reasons.

    -- richard
     
  7. Top Cat

    Top Cat Well-Known Member

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    Different ballistic programs use different mathematical equations to predict the bullet's performance in flight, and even ballistic computers that use the same basic math will likely have been "tweaked" by the software programmer either to improve it, or to make the necessary alterations to avoid infringing intellectual property patents.

    So unless a ballistic program licenses and employs identical software the output will be different.

    TC
     
  8. Terry Scott

    Terry Scott Well-Known Member

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    Thanks all, evidently there is a lot more going on in the math.
    I'll just shoot the distances and get the numbers in reality with the ballistic profiles as my starting point.
     
  9. Sami

    Sami Well-Known Member

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    One of the items I could see being a difference is the "sample rate". What it means is that you will have to pick how often (at what interval) the change in velocity (and drop and drift) is calculated. If you do this at different rates then you will have different answers.

    Easiest way to explain it probably is taking interest calculation as an example. If I loan someone money, would it be best for me to add up interest to the principal every day, every month or just once a year? Every day of course because next day I would be getting interest on the interest. Same applies to ballistic calculation as well.

    If one knows a little about programming, here is an open source ballistic program that you can download and play with the code: http://sourceforge.net/projects/balcomp/
     
  10. Swampy79

    Swampy79 New Member

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    Just to reiterate what everyone has said it is most likely these reasons:

    Between "your" drop chart and the programs is the difference introduced by the unique nature of your rifle.

    Between the different programs, it is undoubtedly a combination of sample rate and resolution (significant figures) in the calculations. Just like the impact of a bullet @ 100m and @1000m (without adjusting the scope), there is a BIG difference between rounding @ the tenths and rounding at the thousandths.

    I personally would either forget about it, or call the software developers, figure out who's using the highest resolution+sample rate, and discontinue use of the others.
     
  11. RMulhern

    RMulhern Well-Known Member

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    FWIW....guys I've been shooting LR a helluva long time.....longer than I care to recall matter of fact. First beginnings was with an 03 Springfield and I've fired many rifles and calibers over 60 years of shooting....all the way back to 1600 yards...or more! AND...my conclusion was over a long period of time that these so-called ballistic charts are good gizmos to con $$$$$ out of people. Now...some will of course rebut that statement but be that as it may....I'll still cling to my own experience and as stated conclusion! Shoot your rifles with the best load that you can get it to develop....record all data related to weather conditions and then use that data to help you in future shootings! Temperature makes a helluva difference I can tell you that from one day to the next and if not taken into consideration...well...you won't be close to what you're gonna want to hit! Once you've found a load combination that works...don't get caught in the trap of constantly chasing a magic new bullet because there are NO MAGIC BULLETS....just raw physics and well established science!
     
  12. Sami

    Sami Well-Known Member

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    There should be no rounding during calculations so that should not be an issue. Calculating trajectory is actually a fairly simple routine, to be honest with. Even with the sampling rate there should not be significant differences unless one program uses very coarse interval.

    For example if I calculate drop using 1ms interval, I get 538.33" of drop and if I switch to 0.1ms I get 537.94". Not a very significant change. This actually leads me to believe there are possible software bugs in the program. As always, it is best if you write your own... :D
     
  13. rscott5028

    rscott5028 Well-Known Member

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    True.

    The latest software is great for plugging in basic parameters, e.g. BC and MV, to get on paper at long distance so that you can confirm your drops.

    They're also good for checking the anticipated correction for different conditions such as altitude, wind, or in-between/unknown distances that you haven't shot.

    It's always best to verify actual dope in the field.

    The ELR guys have to really pay attention to fine details as they get out past 1200 yds or so. ...unless you're just trying to walk it in.

    Given the cost of ammo and barrel life, I think good software is well worth the $$.

    -- richard