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Ballistic App (Shooter) & Atmospheric Conditions For Zero

Discussion in 'Long Gun Accessories and Optics' started by otisrush, Aug 25, 2018.

  1. otisrush

    otisrush Member

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    I'm having trouble thinking something through......

    I understand how taking into account atmospheric conditions for where you're shooting (elevation, temperature, blah blah) is important to accurate ballistics information. However......

    What about capturing atmospheric conditions for when zero is established? I use the ballistics app called Shooter. To get come-ups and ballistics tables for a given round in a given situation there are all kinds of places in the app to get that data input. But when putting a load in for one of your guns (where you document bullet weight, sight-in distance, bullet ballistics coefficient, muzzle velocity, etc.) there isn't anywhere to document atmosphere. (You can select "Zero Atmosphere" and then input a bunch of conditions. The manual states this is for when you zero *beyond* 100 yds.)

    So.....I'm having a hard time understanding this. I would *think* atmospheric conditions would need to be documented for any zero - 100 yds or not.

    Can anyone educate me?

    Thanks.

    OR
     
  2. GarySTL

    GarySTL Member

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    Put in the data when you zero. Your ballistics app will show you the required come ups when you enter the current data.
     
  3. taliv

    taliv Moderator

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    i like shooter and it's my go-to app for ballistics. it's not the most accurate, but it's accurate enough and easy to use.

    if you're zeroing at 100, i do not believe you need to adjust the atmospherics, other than setting the powder temp of the ammo when it was zero'd which is right below and associated with velocity variation. this basically allows shooter to adjust your muzzle velocity based on ambient temp changes. if you zero'd in the summer when it was 90* and chrono showed 3000 fps, and you put velocity varies by 1 fps per degree F, and you shoot 6 months later when it's 30*, then shooter will adjust your MV to 2940 for you when it calculates. you can try this easily a few times to see how it works

    over short distances like 100 yards, things like humidity just aren't going to be significant enough to measure on target.
     
    Gtscotty likes this.
  4. Chuck R.

    Chuck R. Member

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    I use Strelok Pro and zero at 200.

    I also add the atmospheric data for when zeroing, and I make it a point to get a couple decent MV at different temps. I bought a Kestrel 5500 that feeds directly into Strelok. Kind of amazing how easy it makes 1st round hits at distance as long as you feed it the current data.

    Now when it comes to wind shifts and mirage.....you're on your own.

    We used the same basic principle back when we flew a MET (weather balloon) for field artillery.
     
  5. otisrush

    otisrush Member

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    Thanks. This is exactly the type of perspective I was looking for. And it makes sense (now that you said it :) ) that over a distance of 100 yds atmospheric conditions don't have that much of an impact.

    Great point on the powder temp. I'll fiddle with that.

    Thanks a lot!

    OR
     
  6. taliv

    taliv Moderator

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    before you get too hung up on powder temp, change your muzzle velocity by 60 fps and see what difference it makes at 500 and 1000 yards. that will give you further perspective on what you're dealing with. then consider that the powder temp is sort of assumed to be ambient. but if you do something wacky that makes it not so, like keep your ammo in the sun or on your body or leave it in a hot chamber for a minute... don't blame the calculator for missing. GIGO
     
    otisrush likes this.
  7. otisrush

    otisrush Member

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    Very interesting. By reducing muzzle velocity by 60 fps Shooter tells me I have to come up an additional 1) .4 MOA at 500 yds and 2) 1.5 MOA at 1,000 yds. (.243 Win; 115gr Berger VLD Match bullet).

    I haven't been able to get to a place that enables me to shoot those distances since I zeroed this load in and got the MVs. So it'll be interesting to see the results I get on the range as compared to what is theory and from the app.
     
  8. taliv

    taliv Moderator

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    Well .4 moa is a bit over 2” at 500 yards. So in theory that’s the difference your powder temp would make assuming your powder varies 1fps/*F (I’ve seen .4 to 1.7 FPS). Of course the change in air density between your muzzle and target associated with that temp change will add to that.
     
  9. Varminterror

    Varminterror Member

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    That little exercise gives you an idea of how critical a small ES is for long range shooting. If you have 30fps ES, that’s .75moa at 1,000, giving you almost 8” of unresolvable, unpredictable vertical dispersion.

    It’s been several years since I used Shooter, but I know you’re able to input your zero environmental condition. The shift will be inconsequential at 100, but it’ll give you a better correction for your shift at 1,000. Usually the change would only be a tenth mil or two, but I suppose if you zeroed at an extreme, then shot at the opposite extreme, you could end up 3 or 4 tenth Mils off. Add that to whatever vertical dispersion you have from raw precision potential and to whatever vertical dispersion you have from irreconcilable velocity variation, and life gets pretty rough.

    Like @taliv said, though, GIGO.
     
    otisrush likes this.
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