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Thread: No true standard for co-witness optic heights?

  1. #1

    No true standard for co-witness optic heights?

    Over the last couple years I’ve started using taller optic mounts even with fold down BUIS because they give me more FOV over a 12 o’clock mounted light and I can keep my head more upright.

    I’m starting to realize however that what I thought was an industry standard for “absolute” co-witness and “lower 1/3” co-witness is really whatever each manufacturer feels like it should be. I ordered a Geissele RDS Mount and got the lower 1/3 version. It arrived and looked lower than I expect. I double checked part numbers and photos on their site. It is their “lower 1/3” and is taller than their absolute.

    The thing is, it’s the same height as ADM’s “absolute” and the Aimpoint LRP with 39mm spacer (which is also listed as “absolute”). It’s a smidgen shorter than the DD mount with the “lower 1/3” spacer. Did everyone but me already know this? It wouldn’t be the first time I’m late to the party but damn what a disappointment.






  2. #2
    Supporting Business NH Shooter's Avatar
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    https://geissele.com/super-precision-t1-series.html

    Agreed, not seeing a difference between absolute and 1/3 on their site - both appear to be 1.41" above the rail. They do list a 1.93" version and show an obviously taller mount with a different PN. It's as if they're listing three different heights but only actually offer two - I'd get in touch with them for clarification and perhaps an exchange for what you're looking for.

  3. #3
    Quote Originally Posted by NH Shooter View Post
    https://geissele.com/super-precision-t1-series.html

    Agreed, not seeing a difference between absolute and 1/3 on their site - both appear to be 1.41" above the rail. They do list a 1.93" version and show an obviously taller mount with a different PN. It's as if they're listing three different heights but only actually offer two - I'd get in touch with them for clarification and perhaps an exchange for what you're looking for.
    As I recall, Geissele's lower 1/3 height is 1.54" for the T1, MRO & PRO mounts. FWIW, the same as their TA31 mount.

  4. #4
    Modding this sack of shit BehindBlueI's's Avatar
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    Is there a standard for optics?
    Sorta around sometimes for some of your shitty mod needs.

  5. #5
    Site Supporter taadski's Avatar
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    Quote Originally Posted by BehindBlueI's View Post
    Is there a standard for optics?
    I don't know that it can be called a standard, but Larue's SPR mounts place the optic centerline 1.5" above the rail. They make a tall version for clearing PEQ units, etc... that are 1.93.

    In contrast, their dimension for the Aimpoint mounts (with lower 1/3rd witness) is 1.7". If that helps any.

  6. #6
    this link has a good pic that compares the different heights:

    http://soldiersystems.net/2017/05/02...ion-t1-mounts/

  7. #7
    Supporting Business NH Shooter's Avatar
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    Looks like the lower 1/3 to me.

  8. #8
    Quote Originally Posted by BehindBlueI's View Post
    Is there a standard for optics?
    Aren’t we taking about the same thing? Unless an optic has a built in mount, it’s the height of the mount that dictates what our view is through the glass.

    Quote Originally Posted by NH Shooter View Post
    Looks like the lower 1/3 to me.
    It’s definitely the mount Geissele calls Lower 1/3. But as you can see in my pics it’s the same height as what Aimpoint and ADM consider Absolute. Had I know this I’d have ordered the ADM Lower 1/3.

    If only @rob_s had a chart for mounts.

  9. #9
    Hi Risk Customer Services
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    That's the beauty of buying from a company like Scalar Works. They make the sights and they make the mounts so you know they will work together.

    To be fair I did use a set of Daniel Defense fixed iron sights with a couple of different Aimpoints mounted to Scalar Lower 1/3 mounts and never had an issue. I know the Scalar Peak sights are based off the Daniel Defense. The Peaks are awesome but the way.

    I would really like to see what a set of iron sights, fixed or otherwise, designed by Geissele would look like.

  10. #10
    Modding this sack of shit BehindBlueI's's Avatar
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    Quote Originally Posted by El Cid View Post
    Aren’t we taking about the same thing? Unless an optic has a built in mount, it’s the height of the mount that dictates what our view is through the glass.
    So every optic has the lens and/or dot at the same height from it's mounting point?
    Sorta around sometimes for some of your shitty mod needs.

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