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AR Fixed Front Sight with Optics

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  • AR Fixed Front Sight with Optics

    For those of you with optics mounted on your rifles, do you have a fixed front sight? I have an upper with a fixed front sight; I am leaning towards replacing the upper with a factory pinned low profile gas block. I want to mount an ACOG on the rifle, but I have concerns that the front fixed sight is not going to co-witness with the ACOG properly.

    How well do your iron sights co-witness with your optic?
    What optic are you running?
    What mount are you using?
    Can you still use a flip up rear sight with your optic mounted?

    If you have pictures you can post of the optic, and how it co-witnesses I would greatly appreciate it. Ty for recommend.
    Last edited by 1979century; 05-03-2021, 04:35 AM.

  • #2
    My understanding is that an ACOG has fixed magnification, so you'll never be able to see your front sight for a co-witness. You could leave the fixed front sight in place and install a backup rear, but the irons would only be useful as backups with the ACOG removed. In that setup, a quick release mount on the ACOG would make sense.

    I suppose you could get backup irons to co-witness with a LPVO at 1x, but I'm not sure it would be very useful other than if your scope gets completely trashed and you can't see through it. So if you had it on a quick release you could remove it and use the irons. Usually the people concerned about getting their irons to co-witness are using red dots or holographic sights where if the battery fails, you can easily use the backup irons.
    NRA Life Member
    NRA Basic Rifle Instructor

    I was thinking of his cannon.


    • #3
      Do you already have a acog? If not then this could be a good option .
      I have a front site post with mine and I can't see the front site post.
      I'm not sure if using a riser might be an option to have BUIS? I'm STIHL out of conditioner!!
      Finally joined the ranks of broke homeowner
      Am I short stroking or going to fast?

      I know he has a bush


      • #4
        The ACOG is not meant to be used with BUIS, and you' never get it to co-witness couple of reasons.

        1) The ACOG is a fixed 4x magnification. That doesn't work with iron sights.
        2) The ACOG is so long that it takes up the entire lower receiver. There's room at the back of the receiver to install a flip up sight, but you won't actually be able to flip it up unless you remove the ACOG.

        A real ACOG from Trijicon is nearly impossible to kill, so the chances of you ever needing to use the BUIS are very slim. So you can either leave the fixed front sight and have a flip up rear installed with quick release mount or toolless mount on the optic OR the other option is to get a set of 45* offset sights. The 45's are meant to be used in conjunction with scopes or optics like the ACOG.

        Here's a good article on offset sights and their pros/cons.
        Sticky Lips at High Noon!


        • usmcveteran
          usmcveteran commented
          Editing a comment
          I think the actual manual for acog says after making adjustments on scope you should hit it to make sure everything is in position lol.

      • #5
        Sticky Lips at High Noon!


        • #6
          Sticky Lips at High Noon!