A primer on properly setting up Chairgun

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    spinj
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    Hey all, this is for those who plan on using Chairgun for obtaining accurate aim points and turret click values.  If you are having difficulty viewing the images on your PC, hold down the “Ctrl” key and tap the “+” key on your keyboard to enlarge the scale of view (for Windows users).







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    FearnLoading
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    Thanks for this one. It’s very helpful. 

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    spinj
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    You’re welcome sir.

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    AZBOBCAT
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    Well done 

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    spinj
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    Also, what’s not in the article is the need to input the correct environment elevation, temperature, humidity, and air pressure values into Chairgun to increase ballistic precision.  I use the Yahoo Weather app to give me the temperature, humidity, and air pressure information.

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    spinj
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    Thanks AZBOBCAT. 

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    Zephyr
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    I have been pondering the POI change due to the slight variation in pellet weight within a tin. I cannot see how to get Chairgun to calculate this, any ideas?

    I suspect the change in POI will only be a few ‘thou’, but I would like to know.

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    spinj
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    “Zephyr”I have been pondering the POI change due to the slight variation in pellet weight within a tin. I cannot see how to get Chairgun to calculate this, any ideas?

    I suspect the change in POI will only be a few ‘thou’, but I would like to know.

     

    
With quality pellets like JSBs, I don’t worry about weight variation even though there are various slight “hundredths-of-an-inch” differences in a tin.  I don’t see a POI difference at the distances I shoot at, even at the farthest I shot my powered-down Cricket at, which is 50 yards at the range not too long ago.  If you really want an exact pellet weight to use, then I suggest you weigh your pellets.  Choose which weight among those that you’ve managed to sort all the pellets into and use that one to plug into Chairgun.

    Cheers! 

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    nvelkhunter
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    Who can tell us about pressure values used in Chairgun? If you call up weather.com you find a pressure number for your location, but I don’t think that is your ambient pressure. It appears to me that weather.com converts ambient pressure to an equivalent pressure at sea level. As I understand it you should use ambient value and not sea level corrected value.

    Example
    Weather.com 30.13
    NOAA national weather service; Altimeter setting = 30.13 & Station pressure = 25.363

    Should one use the 25.363 as the input for ambient pressure in Chairgun?
     

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    Kim
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    “Zephyr”I have been pondering the POI change due to the slight variation in pellet weight within a tin. I cannot see how to get Chairgun to calculate this, any ideas?

    I suspect the change in POI will only be a few ‘thou’, but I would like to know.

    
Me too.  I’ve only puttered with the program but haven’t found a way to hold fpe constant, vary weight slightly (0.1grain), and observe the predicted shift in POI.

    The calculation isn’t that simple.  Though heavier pellets travel slower (for a given fpe) to target, they also have higher BC.

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    Zephyr
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    “spinj”

    
I do weigh my pellets and select a single weight (+/- 0.1%). I have also noted when doing this that it is rare to get head size variation in single weight pellets. I like to understand the theory and maths behind the empirical data. 

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    Zephyr
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    “Kim”Kim

    
The controlling factor seems to be the programme using the ‘zero’ as a fixed datum rather than allowing it to be a reactive output.

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    spinj
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    “Zephyr”

    “Kim”Kim

    
The controlling factor seems to be the programme using the ‘zero’ as a fixed datum rather than allowing it to be a reactive output.


    You are correct.  I think it is better, though, that Chairgun functions this way because it keeps data as empirical (thus precise) as possible.  If the zero were to be a reactive output it will only cause the program to further “guess” what the scope height will be, and thus, the ballistics of the projectile.  Less guesswork and more certainty is much better, IMO.    

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