Can't get ballistic calculations to agree

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by lisagrantb, Nov 25, 2011.

  1. lisagrantb

    lisagrantb Well-Known Member

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    Here is the problem: Actual drops recorded are as follows.
    1200 yards 8.3 mils
    1057 yards 6.4 mils
    496 yards 1.6 mils

    I must enter numbers like MV 3380 and a BC of .8 with A DK of .445 for a ballistic program to agree with the actual drops.

    I have tried this three times and the results are the same. I verify my zero (100 yards) dial 8.3 mills for 1200 yards and get a direct hit dial 6.4 mills for 1057 then dial 1.6 for 496 yards then reconfirm my zero again.

    Here is the set-up 7mm WSM 27” brux barrel Defiance long action and Nightforce nsx 5.5X22X56 scope mounted 2.7” high. I have checked the velocity with 2 cronos. And am getting 3034FPS @ 72 degrees 29.99” and 60 percent humidity. I’m shooting the Berger 180 hybrid VLD with a BC of .674 according to Bryan Litz’s book. I have calibrated the scope and it's actually .1 mills per click.

    Why can’t I get my ballistic program to get even close with the above numbers?
     
  2. Loner

    Loner Well-Known Member

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    Do you have your zero info entered in? Are you using zero info in weather?You appear to be using corrected baro not actual. Do you have the program set right for it? What is the
    wind you are shooting in? What program are you running? A lot you aren't telling us.
     

  3. lisagrantb

    lisagrantb Well-Known Member

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    I’m using Field Firing Solutions and I have checked and rechecked my settings (that is not to say I’m still not making a mistake. I am very familiar with this program and have gotten dozens of other guns/loads to work great without a problem. I take all actual atmospheric data with a Kestrel 4500 and enter it into the program as well as keep records on each shot while trying to develop a drop chart . Can you input the numbers I have into another program and come up with a reasonable solution.
     
  4. milo-2

    milo-2 Well-Known Member

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    Lisa,

    Have you tried using density altitude instead of entering all the other data?
    Your kestrel has that feature. Using DA has helped me more than once.

    Altitude here is about 4600 feet, I've seen the DA at 3500ft on a pre cold front day, to 8700ft on a 90 degree day. Crunch those numbers and you can see things change quickly.
     
  5. Mike6158

    Mike6158 Well-Known Member

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    Take a look at the G7 Ballistics calculator. The link is dead in the middle of the menu bar on the forum page. Don't overlook the Trajectory Validation button
     
  6. woolecox

    woolecox Well-Known Member

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    I can't get the G7 online calculator to come up on my Mac. Do you have to access it through a Windows PC?

    I want to compare this program to some of the others I'm running. From what I have been reading and viewing on the videos, I really like the features of this program.
     
  7. Mike6158

    Mike6158 Well-Known Member

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    I have a Mac Pro sitting to the left of my PC (I use it mostly for photo and video editing). I switched to the Mac and the G7 link worked fine. I had to log in but I expected that. I also open it on my PC
     
  8. woolecox

    woolecox Well-Known Member

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    Hmmm.... I must have something blocking it on the Mac.
     
  9. Mike6158

    Mike6158 Well-Known Member

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    Java or Javascript maybe? Popups?
     
  10. LouBoyd

    LouBoyd Well-Known Member

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    Did you enter the value for the centerline of the sights over the centerlilne of bore correctly? It seems like a small small issue but it can really screw up the calcualated values. The default balues in the programs can be way off. Measure it, don't guess. Exteriior ballistics programs are calculated relative to the muzzle, not the bolt face or the scope objective. Usually it doesn't matter, but it will if a long range zero zero is used where the scope and the bore aren't close to parallel.
     
  11. lisagrantb

    lisagrantb Well-Known Member

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    Ok here is the latest went to the range with the following results.
    Pressure 29.8”, 66 degrees, 96% humidity, 5mph wind from 280 degrees.

    1) First second and third shots was at 100 yards to confirm cold bore shot and zero on a cold but fouled barrel. It shot a nice .5 MOA group right on the bulls eye.
    2) One shot at 496 yards, dialed 1.7 Mills and .3 mills left for wind, dead center hit less than 1.5” from poa.
    3) Dialed 3.1 mills up and .6 mills left windage, fired one shot at 700 yards and again dead on hit a little left because I wasn’t watching the wind.
    4) Dialed 6.6 mills and .7 left for wind for a 1057 yard shot, and again another dead on vertical hit.
    5) Checked zero again with one shot and it hit within .3 moa of the shots in step 1
    6) Repeated steps 2 through 4 again with the same results.
    7) Dialed .4 mills up for a 267 yard shot and hit about 1” high, that could have been me.
    8) Repeated step 5, now I have a .75moa 5 shot group with the center about .25” high from poa.

    All in all I would call this a successful trip to the range, hit every target with a high level of accuracy (for me anyway) I was pleased. Now here is the problem. I hit the targets using the computers calculations, but this is what I had to input in the computer. MV 3388, G1 BC .675, DK .464. There is no way I’m going 3388fps and the DK is way off. I’m getting the correct answers but I know the inputs are bogus. I’m still scratching my head on this one.
     
  12. Mike6158

    Mike6158 Well-Known Member

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    Well... I went to Berger's site and downloaded their ballistic program. I plugged all of the data in, set the output units to MILS, and created the following drop chart.

    Before I post that here's my input data (from your first post):

    Cal: .284
    Weight: 180 grains
    G7 standard selected
    G7 BC from the website: 0.345 (G1 = .674)
    Muzzle velocity: 3034

    Temp: 72°F
    Pressure: 29.99
    Humidity: 60%
    Wind 0 from 3 o'clock

    Site height: 2.7"
    Zero Range: 100 yards
    Look angle: 0°

    100 0.00
    200 -0.20
    300 -0.69
    400 -1.28
    500 -1.95
    600 -2.67
    700 -3.46
    800 -4.32
    900 -5.25
    1000 -6.25
    1100 -7.34
    1200 -8.53
    1300 -9.82
    1400 -11.23
    1500 -12.78

    Looks pretty close to me. Which ballistic program are you using?
     
  13. lisagrantb

    lisagrantb Well-Known Member

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    Field Firing Solutions, Yea I can get kinda close with good or realistic inputs but to make it really fit the actual drop that is where it starts going down hill. You would think some fine tuning would bring it right in but I have not found that to be the case
     
  14. Mike6158

    Mike6158 Well-Known Member

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    I may have missed it but what's the barrel's rate of twist?