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Thread: Explanation of Co-Witness

  1. #21
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    I'm confused. How is POA/POI different between irons and red dot optics? If zeroed for the same range, using same ammo, the difference between the two to me is nil...group size with the red dot is smaller than the irons, unless I'm shooting a rifle-length sighted gun.
    Nemo me impune lacessit

  2. #22
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    There are different offsets depending on Ammo types and Optics and Lasers.
    Brett W

    Elite Defense
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    FN Senior Manager of Assault Weapons - SCAR Program 2006-2010
    Former Troy Industries Inc Director of Operations 2003-2006

    Each Warrior wants to leave the mark of his will, his signature, on important acts he touches. This is not the voice of ego but of the human spirit, rising up and declaring that it has something to contribute to the solution of the hardest problems, no matter how vexing!
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  3. #23
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    In my Arm chair commando opinion:

    The only right way to do this is to first sight in your BUIS(s) and then "co-witness" your dot/scope/whatever.

    That way if you ever have an optic failure you know for certain your BUIS(s) are calibrated for POA.

  4. #24
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    Quote Originally Posted by Snake RAH View Post
    I'm confused. How is POA/POI different between irons and red dot optics? If zeroed for the same range, using same ammo, the difference between the two to me is nil...group size with the red dot is smaller than the irons, unless I'm shooting a rifle-length sighted gun.
    it's not different - it's the same, at the distance both are sighted in, and as long as you're looing through the irons when sighting the dot. but if you move your head up and look over the irons, the POI will be different for ranges OTHER than what you sighted them both in.

  5. #25
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    It will actually be different.

    Example:
    @ 25m If you have X sight, your POA will be center mass on the Target. However, you need to put your POI approx 1.23 inches to the 12 o'clock, for a proper 300m BZO of that sight or optic/red dot.
    Brett W

    Elite Defense
    Vice President of Domestic Sales and Marketing


    FN Senior Manager of Assault Weapons - SCAR Program 2006-2010
    Former Troy Industries Inc Director of Operations 2003-2006

    Each Warrior wants to leave the mark of his will, his signature, on important acts he touches. This is not the voice of ego but of the human spirit, rising up and declaring that it has something to contribute to the solution of the hardest problems, no matter how vexing!
    -Pat Riley

  6. #26
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    Originally post by DocGKR

    I zero my irons first.

    Then I zero my optic.

    When using my preferred red-dot optics (Aimpoints in LaRue mounts) in every case to date, the red-dot has been perfectly centered on the iron sight front post tip when looking through the irons and optic simultaneously. In other words, my irons and red-dot have the same POA/POI and are CO-WITNESSED.

    If my red-dot and BIS have been co-witnessed during the initial zero, then at the beginning of each shift/operation I can flip-up the BIS and ensure the red dot is co-witnessed as a quick verification that my zero has not shifted. Then I flip-down the BIS and go about my business. In my world, that is the main benefit of co-witness.
    This is the technique I was taught with Big Green and still use today.

    It has worked for me for me as long as I have been using a Aimpoint.

    If my Gun takes a hard hit on the deck... I pop up the BUIS and can verify my red Dot zero to My BUIS.

    As to the whole 1/3rd Co witness vs. a "true" co-witness.....

    Never got wrapped around the axle on that.

    I like my Irons usable and within the Aimpoints field of view, but not dead center..

    I think to many shooters get wrapped about where there Irons are within that field of view..

    The way I look at it..If I'm outside of transition range and the dot fails, the Irons go up and I shoot them until I can get the dot sight back up.. if the dot sight "ain't" coming back up for a while, I'm swinging a throwlever and ditchin it(Stashing it to fix/replace at a later date) and going with all Irons. So true co-witness or 1/3rd co-witness is moot at that point.

    I guess for me the Aimpoint is like my regular brake and the BUIS's are like my Parking brake, as long as it's in a familiar location, and I test it from time to time to see if it works... I'm good to go...I don't really give it much more thought then that....

  7. #27
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    Quote Originally Posted by SinnFéinM1911 View Post
    It will actually be different.

    Example:
    @ 25m If you have X sight, your POA will be center mass on the Target. However, you need to put your POI approx 1.23 inches to the 12 o'clock, for a proper 300m BZO of that sight or optic/red dot.
    we're saying the same thing in two different ways. but the difference is in the details.
    i think there's some confusion - using the dot when looking THROUGH the irons and using the dot when looking OVER the irons. when looking through, POA/POI is the same, when looking over, it's different.
    i believe your example above is when using the dot OVER the irons, not looking through them.

  8. #28
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    Ok, I only read half...

    Putting my Eotech on the LaRue 110 I can still get a co-witness.

    Removing the LaRue and mounting the Eotech on my flattop gives me an ABSOLUTE co-witness where the dot is just about at the tip of the irons.

    Right?

  9. #29
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    MM and SF1911,

    I guess I have some more shooting to do. I know that I don't shoot my optic while looking through the irons, since I haven't taught myself to use all that sighting stuff. It's one or the other, but not both at the same time.

    In the end, when the optic and irons are both zeroed to the same range, I find that if I do look through the irons, the optic (for me, usually the EOTech) reticle is on top of the irons.
    Nemo me impune lacessit

  10. #30
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    if you're looking through the irons, the eotech dot can be adjusted so that it's on top of the front sight whether or not it's in a LaRue mount or right on the flat top, assuming you've adjusted the dot and irons to each other.

    i just chatted with brett on the phone - we're on the same page.

    here's my .02 on the terms:
    co-witness: to me, this just means that i'll be able to look through my irons anywhere in the optic window or tube, and be able to adjust the irons without removing the optic. the dot may or may not be adjusted to sit right on top of the front sight when you're looking through the irons. for example, you may have your irons adjusted for POA/POI at 25M and your dot at 100M. when you look through the irons, the dot will NOT be sitting on the front sight. they're zero'd for different ranges. in simple terms (to me) 'co-witness' means 'i can see my irons through my optic', regardless of how they're zero'd.

    absolute co-witness: i think some have accepted this to mean that the irons are centered in height in the tube/window. i don't think it matters - that's just how much of the irons you want in your sight picture when you're looking through the optic. what it means to me is that regardless of whether the irons are in the lower third or centered in the optic, you've adjusted either the dot or irons to COINCIDE when looking through the irons. that way you can check them against each other. so, (to me), 'absolute co-witness' mean the dot is right on top of the front sight WHEN I LOOK THROUGH THE IRONS.

    here's where the details (and confusion) comes in. if you've co-witnessed the sights, POA/POI will be the same WHEN YOU LOOK THROUGH THE IRONS. if you normally use the dot sight by looking OVER THE IRONS (as in a lower third co-witness), the POA/POI will be the SAME only at that distance the sights were zero'd at (let's say 25M). at all other distances, they will diverge. this is because when you look over the irons, with your eye half an inch above the line of sight through the irons, you've now introduced an offset to the dot +(as it 'follows' your eye, being parallex free), and created a new line of sight that is not parallel to the iron line of sight. both lines of sight will cross where you've zero'd them at, but only at that one distance, which is why your POI will be different from POA for the irons and dot when looking OVER the irons. not sure if that makes sense.

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