BallisticsLong Range ShootingMarksmanship training

Understanding your Ballistics Calculator Atmospherics

Understanding what your Ballistic Program is doing.

We all have our favorite ballistic program we prefer to run.  Whether it’s on our phone, watch, Kestrel or other dedicated device, the program is with us every time we are shooting.  Each range trip we get the device out, update the environment, input our target distance, dial our scope, shoot the target and if done correctly, we hit the target. We hit targets at incredible distances in different weather conditions or physical locations because our ballistic program tells us what to do.  Have you ever wondered what that magic little program in the box is actually doing? Most shooters, especially new shooters, read the shooting solution from the ballistic program and blindly use it yet never truly understanding what changes that data and when the inputs really matter.

Before we begin

First, we must understand that we need to “true” our software to what our rifle is doing.  If we shoot the target and need 3.5 mils (12.0 MOA) to hit at 600 yards, we need to adjust our ballistic program to show the same 3.5 mils.  Ballistic programs are not meant to magically give us our drop information straight out of the box. We must true the program to the weapon system. After the truing is done, the real function of the ballistic program can be used.  

The intended purpose of a ballistic program is to adjust our shooting solution for the changing atmospherics and location at which we are shooting.  As the temperature rises, the solution (mils of drop) is a little less than when the weather is cold.  If we rise 5,000 feet in elevation, our solution is different from where we started. Shooting in the winter and summer have different ballistic solutions.  This is the real function of the ballistic program: to provide a ballistic solution under different environmental conditions.

How can we understand what the program is doing?  I’m not talking about the technical calculations it’s performing but rather the end result, the output data. What is changing the output come-up and by how much?  We can study the concepts of what affects our bullet: hot vs cold, humid vs dry, barometric pressure and elevation changes.  But, how do we understand what this will really do to our bullet path and to our ballistic program results? An eye opening simple exercise is to fill out density altitude data sheets and change one variable at a time on each sheet to see the effect. 

Here are several different density altitude sheets for my 6.5 Creedmoor shooting 130g ELDs at 2900 feet per second.  On each sheet I have changed one variable (value in red) to better understand how much it affects the program output or the come-up.  The blue line represents a 0.1mil (0.3 moa) change in drop and the red line is 0.2 mil (0.7 moa) change in drop from my home range environment which is the shaded column near the center.

Atmospheric Changes

Temperature – Changing temperatures will affect our bullet path the most.  Most shooters have never taken the time to find out how much it will change the path or at what distance it starts to take effect.  The chart below shows I need to have more than 800 yards of distance or a change of 30 degrees F to have a 0.2 mil (0.7 moa) change in my bullet path. That is 5.8 inches of change at 800 yards.

Pressure – Pressure changes due to weather or altitude can affect our bullet path.  This chart shows I need around 1,000 yards of distance to start thinking about it affecting my bullet path.

Density Altitude (DA) – Density altitude is combining the changes of the temperature and pressure.  The chart below shows I need 700 yards of distance and change more than 2000 DA to start affecting my bullet path enough to worry about it.

These charts will be slightly different for any combination of caliber, rifle, and ammunition.  Try this for your rifle to see what you find.

What we can truly learn from this is when and how far these environmental changes start to affect our bullet path.  It can show us when we need to start thinking about these things.  If I am shooting 300 yards do I need to take this into account?  What about 800 yards?  If we can accept being +- 0.2 mils (~0.7 moa) of error we will see my 6.5 Creedmoor will need to shoot past 900 yards with a temperature swing of 30 degrees to start making an effect.  We can start to make mental notes about how much elevation change, temperature change or pressure changes we can absorb without needing to change our ballistic data. Or be able to recognize when it’s time to refer back to the ballistic program and update our environmentals to get a better ballistic solution.

Understanding what comes out of our little magic box (program) is important. It’s even more important to understand what is going into that magic box to make the drop data change. We want to understand how much change or distance will affect our ballistic solution.  After doing this exercise I know my bullet path will not change considerably when I’m shooting 400 yards if it’s 20 Degrees in winter or 80 degrees in summer.  This ultimately helps me diagnose errors in my shooting or weapon system if something starts to go wrong. I can quickly address a high or low impact by having a basic knowledge of what my system will do under today’s conditions.  Was the error me, the rifle, ammunition or the ballistic solution?  Now I can eliminate or blame the computer.

At a minimum, I won’t be that guy at a competition twirling my Kestel to update my environment at every stage.

Ted Hoeger – @Jackmaster

Don’t forget to check out our Book, Precision Rifle Marksmanship

Owner of Sniper's Hide, Bigfoot, The Loch Ness Monster, Aliens, & UFOs

Baron23

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    Than you, Frank. Good read.

    I’m pretty new at this and have been using online calculators like Hornday 4DOF.

    Where do you get your density altitude figures from? Enter absolute pressure and temp and calc gives you DA or??

    Back when I was in USAF (we were still flying biplanes) we used circular slide rules or just paper charts and entered w pressure and temp. But it’s been so long now that I may well be delusional.
     

    ACard

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    Thanks for the knowledge dump Frank, this is certainly s week spot in my abilities, oh and dude... the Crayon box tops it off😂

    Semper Fi!
     
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    pmclaine

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    Ohhhhhh! Bed time reading.

    Im going to light some candles, make a hot chamomile tea, and wear something comfortable to read this.

    Turn off wind 1, don't put in latitude, shitcan spindrift it's all so sadistic and misunderstood by me....

    Im rubbing my nipples.
     

    pmclaine

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    They actually changed it, turning off Wind 1 does nothing anymore they are sync'd
    Sweet.

    Haven't even read Mr Masters article and I am already learning.

    Are Mr Masters parents aware........never mind.
     

    isofahunter

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    Ohhhhhh! Bed time reading.

    Im going to light some candles, make a hot chamomile tea, and wear something comfortable to read this.

    Turn off wind 1, don't put in latitude, shitcan spindrift it's all so sadistic and misunderstood by me....

    Im rubbing my nipples.
    You don't get out much do you? Probably best for the rest of us.
     
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    Jack Master

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    Than you, Frank. Good read.

    I’m pretty new at this and have been using online calculators like Hornday 4DOF.

    Where do you get your density altitude figures from? Enter absolute pressure and temp and calc gives you DA or??

    Back when I was in USAF (we were still flying biplanes) we used circular slide rules or just paper charts and entered w pressure and temp. But it’s been so long now that I may well be delusional.
    I don't have a fancy kestrel so When I can, this is the website I use to calculate DA.
    https://wahiduddin.net/calc/calc_hp.htm

    otherwise I calculate DA with a chart.
    Screenshot_20200917-205745_Slides.jpg
     

    Baron23

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    pmclaine

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    Good read.

    My after consumption summary is that in a typical shooting session things will likely not change so much during the day that you need worry about confirming data for each shot or stage.

    As a new Kestrel owner what Im finding useful is I now have real weather data not just "Feels like 65".

    Im also finding I likely overestimated wind, If i felt moving air and saw the flag moving Id assume "Probably 8 mph or 10" but Im seeing now its 2-3 mph.

    I kind of discount wind at my shooting position a bit.

    My local range it seems to never be lateral to me its either at my back or in my face so little effect. At other places I frequent it will be a bowling alley with an opening to a lake on one side or the other, perhaps some other wind effecting feature and what I get at the shoot position matters but what I see down range kind of makes it matter less so and I have to still account for shit my tools cant help me with.

    I have to get mine better trued up but if I do so, me being a plinker, I might be shooting 175s one day, maybe Ill come across a Deal on 168s later - will the device store truing when using varying ammo in the same rifle? Do I want to go through that?

    Ive only had limited chance to play with these tools - an upgraded Kestrel Sportsman paired with a Bushnell Conx. My ranging ability and weather data have been enhanced greatly but Im still hitting targets with my guns just as I did before.

    Still finding my data book is my most important aid and really this tools exist to improve what gets recorded in there.

    You big sky country, prairie shooters, likely to have a more "consistent" wind might put more emphasis on your at shooter wind data. That wind at shooter is probably going to have a constant and consistent effect on flight as opposed to my typical bullet flight of "Wind from behind, oh oh lake - wind from the right, hey a hill that swirls the wind from right to left, power lines - wind from the right again"
     
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    jaybic

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    anyone know where one might find blank charts like this to fill out for their own use?
     

    TJ Stedke

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    Oct 8, 2020
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    Good read.

    My after consumption summary is that in a typical shooting session things will likely not change so much during the day that you need worry about confirming data for each shot or stage.

    As a new Kestrel owner what Im finding useful is I now have real weather data not just "Feels like 65".

    Im also finding I likely overestimated wind, If i felt moving air and saw the flag moving Id assume "Probably 8 mph or 10" but Im seeing now its 2-3 mph.

    I kind of discount wind at my shooting position a bit.

    My local range it seems to never be lateral to me its either at my back or in my face so little effect. At other places I frequent it will be a bowling alley with an opening to a lake on one side or the other, perhaps some other wind effecting feature and what I get at the shoot position matters but what I see down range kind of makes it matter less so and I have to still account for shit my tools cant help me with.

    I have to get mine better trued up but if I do so, me being a plinker, I might be shooting 175s one day, maybe Ill come across a Deal on 168s later - will the device store truing when using varying ammo in the same rifle? Do I want to go through that?

    Ive only had limited chance to play with these tools - an upgraded Kestrel Sportsman paired with a Bushnell Conx. My ranging ability and weather data have been enhanced greatly but Im still hitting targets with my guns just as I did before.

    Still finding my data book is my most important aid and really this tools exist to improve what gets recorded in there.

    You big sky country, prairie shooters, likely to have a more "consistent" wind might put more emphasis on your at shooter wind data. That wind at shooter is probably going to have a constant and consistent effect on flight as opposed to my typical bullet flight of "Wind from behind, oh oh lake - wind from the right, hey a hill that swirls the wind from right to left, power lines - wind from the right again"
    Relative to the question about a device "storing truing" when using varying ammunition in the same rifle, every rifle/ammunition combination is different, even different lots of the same ammunition can have differences that are significant enough to throw the "truing" off, so for the best results with ballistics calculations (especially at longer distances beyond 1000 yards), it's absolutely essential to have as much consistency and precision in both your rifle (barrel cleanliness, barrel temperature, contact points, contact pressure, and even shooting surface from a jump angle perspective) as well as your ammunition (bullet type, grains, muzzle velocity, seating depth, powder lot, primers, brass, etc...). Variances in your rifle or ammunition will throw your DOPE off, and significant variances such as different ammunition can shift your POI by several feet at longer distances.
     

    6.5SH

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    Jul 24, 2020
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    Hi Ted - wouldn't happen to have an editable version of those comparison pdfs, would you????
    Simply print that JPG to a PDF file, then you can use Adobe Acrobat Reader DC to fill it out.

    EDIT:
    Will just attach a converted one.

    Edit 2: and missed Jack already had, just use Reader DC and you can fill them out on your computer.
     

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    Baron23

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    Simply print that JPG to a PDF file, then you can use Adobe Acrobat Reader DC to fill it out.

    EDIT:
    Will just attach a converted one.

    Edit 2: and missed Jack already had, just use Reader DC and you can fill them out on your computer.
    Thanks...got it going now.

    The files I downloaded from Jack's post were indeed a pdf but I had a bit of trouble figuring out how to edit. Adobe kept trying to sell me full Acrobat.

    But I have found that if I hit the "Fill & Sign" button on the left, it indeed let's me add text.

    Thanks for the reply.
     
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