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Thread: Lower 1/3 and irons perceived relation

  1. #1
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    Lower 1/3 and irons perceived relation

    Trying a Holosun lower 1/3 mount after using an Aimpoint PRO(closer to absolute).

    I know the dot and iron sights are 2 separate zeros, but usually looking through irons with an absolute will appear to have the dot sitting center on the top of the front sight.

    Does that carry over to lower 1/3 as well? Or will the dot appear to be sitting noticeably higher than the front sight when looking through the irons?

    Due to weather and other events I haven't been able to make it to the range this week so trying to get close before live fire.

  2. #2
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    Depends on the optic and it’s parallax behavior. In theory something with no parallax like an EOTech would line up exactly on the tip of the front post regardless of the height of the window.

    The Aimpoint T/H2 causes light refraction so the image of the red dot and irons as zeroed will not match.

  3. #3
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    Yep.

    Aimpoint Micros have parallax.

    Putting rhe dot right on top of the irons will get you on paper, but you’ll have to fine tune it some.

  4. #4
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    Yes, like mentioned above. On my Eotech EXPS 3 proper sight alignment with irons has my center dot exactly on the tip of my front sight post.

    Sent from my SM-N970U using Tapatalk

  5. #5
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    If I zero my Aimpoint and my irons to the same POA/POI, when I go to the irons the dot is TDC on the front sight post.

  6. #6
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    I am sure there is parallax to a degree but my H2 is on a lower 1/3 mount. It is zeroed at 50 and confirmed at 200. My irons are the same. When I look through the irons, the dot is split in half by the post. Round show zero POI shift on mine. Same thing is true for a Sig Romeo4 on a lower 1/3 mount....

  7. #7
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    Quote Originally Posted by 17K View Post
    Yep.

    Aimpoint Micros have parallax.

    Putting rhe dot right on top of the irons will get you on paper, but you’ll have to fine tune it some.
    This I can confirm - but if you have it planned out right, you start off on paper, and should be able to get a 50yd zero in a dozen rounds, then shoot for confirmation. You'll be on paper, and strangely my windage is always a bit off this way too, but it's close enough that I don't lose count on clicks
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    Lower third co-witness, was like trying to get used to no-line bifocals. I couldn't on the former, and STILL can't on the latter... 10 years later...
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  9. #9
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    I have several mounts (unmounted) that I am unsure if they are absolute or lower 1/3. How would one measure it to determine one from the other?
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  10. #10
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    Quote Originally Posted by prepare View Post
    I have several mounts (unmounted) that I am unsure if they are absolute or lower 1/3. How would one measure it to determine one from the other?
    This is a short video by PA that has the best explanation I have seen on the difference between absolute and 1/3.

    https://m.youtube.com/watch?v=ogX-cIx9hpk&autoplay=1
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