FOC and Sighting

Discussion in 'Equipment Reviews' started by Mkwa Hunter, Oct 3, 2013.

  1. Mkwa Hunter

    Mkwa Hunter Weekend Warrior

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    So tonight I spent the evening calculating my FOC. I sighted my new bow @ 20,30,40,50,& 60 with with the following arrow:
    Cabelas Striker X-Treme 9.3 GPI at 34 inches with a 100 grain field point giving me a 10.00% FOC

    So what I am trying to do is not have to re-sight my bow in for my new FMJ 340 11.3 GPI at 31 inches. It is my understanding in order to do this I need to have my FOC to be equal, which is 10%. Is this correct?

    If it is, then I would be my calculation that I would need a 150 grain tip to give me the 3.15 inches I need. See picture for my calculations. [​IMG]


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    Mkwa Hunter, Oct 3, 2013
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  3. Mkwa Hunter

    Mkwa Hunter Weekend Warrior

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    Sorry I forgot one thing. It seems the current arrows are 313.875 GPI and the new arrows are 355.95 GPI. So if I used a 75 grain vs a 100 grain field tip would this help?


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    Mkwa Hunter, Oct 3, 2013
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  4. tfox

    tfox Grizzled Veteran

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    The foc is irrelevant. The arrow weight and diameter will determine how the pin gap and impact point will work out.

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    tfox, Oct 3, 2013
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  5. tfox

    tfox Grizzled Veteran

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    Spine will also have an effect on the left/ right impact as well.

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    tfox, Oct 3, 2013
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  6. tynimiller

    tynimiller Legendary Woodsman

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    Any change in season or out of season means you must start from scratch and re-tune your bow. Otherwise you're choosing to not do your utmost in being prepared and ready to put forth the best shot if one is presented when you hunt.
     
    tynimiller, Oct 3, 2013
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  7. Mkwa Hunter

    Mkwa Hunter Weekend Warrior

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    I have decided to leave my bow sight to my Cabelas arrows and leave the FMJs in the box. This way I'm confident with my shots. I am open to you feedback though.
     
    Mkwa Hunter, Oct 3, 2013
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  8. Mkwa Hunter

    Mkwa Hunter Weekend Warrior

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    TFOX, help me understand your comment. My arrow weight is Cabelas: 313.875 and the FMJ are 355.95. how do you find diameter?
     
    Mkwa Hunter, Oct 3, 2013
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  9. tfox

    tfox Grizzled Veteran

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    The diameter will determine how high or low the arrow sits on the rest. This will raise or lower an arrows impact when changing from one to the other.

    Some manufacturers will list the diameter, some archery programs will also list it but the best way is to use some calipers or micrometers and check it.

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    tfox, Oct 4, 2013
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  10. Mkwa Hunter

    Mkwa Hunter Weekend Warrior

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    I found the Cabelas are 0.298 and the FMJ are 0.340. What does this mean now?
     
    Mkwa Hunter, Oct 6, 2013
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  11. tfox

    tfox Grizzled Veteran

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    Fmj is bigger so it will sit higher on the rest and hit higher at short distances, until the faster speeds of the lighter arrow crosses the trajectory path of the heavier.


    If that makes sense.
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    tfox, Oct 6, 2013
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  12. Mkwa Hunter

    Mkwa Hunter Weekend Warrior

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    Man...tfox...this is interesting stuff...
     
    Mkwa Hunter, Oct 6, 2013
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