Explanation of Co-Witness

[militarymoron]

MM and SF1911,
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.

yes, agreed, as they should be when 'absolute co-witnessed' (which has nothing to do with center/lower third position).

[SuicideHz]

So what you are saying MM is that if the dot isn't sitting on top of your irons then it's still absolute cowitnessing if you can move your dot so that it sits on top of the irons?

For instance, on my Eotech on LT110, the dot can be moved basically anywhere in the window. I have a KAC 300m flip rear so it's almost always down. I CAN if I want, adjust my view so the dot sits on top of my front iron, but that's not an absolute cowitness because I would think that to absolute cowitness the dot would have to sit on the front sight when the front and rear are lined up correctly.

[militarymoron]

suicide, not sure if i understood what you meant. the dot is only 'absolute co-witnessed' if it's sitting on the front sight WHEN you're looking through the irons (front lined up with rear). if your rear sight is down, and you move your head so the dot is on top of the front, you're just lining up your eye to where it'd be when looking through the rear sight if it were flipped up and you had them lined up.
when you're not looking THROUGH the irons, the dot can be anywhere in the window - its position relative to the front sight is irrelevant - top, to the side, lower etc. so, in other words, when your rear sight is flipped down and you're using the dot, ignore the front sight and don't bother trying to put the dot on it.

[Redhat]

Do the procedures in the Army FM work?

[SuicideHz]

MM- yes, that's exactly what I was getting at. It's just that when I gave my interpretation and I first mentioned "absolute" I thought you were making a point to state something else and not just corroborate.

Absolute is when the rear is flipped up that the irons AND dot align (somewhat.)

I can have my irons zeroed perfectly at 50 and my Eotech zeroed perfectly at 50 but when I use them together the dot isn't perfectly on top of the front. I think that's just a little error introduced by each and how they are used that was touched on earlier by someone.

For instance, If I take my 512 off of the mount and put it on the flattop and flip up the KAC, the dot is off to the left on top of the front post. I think that's due to the Eotech's clamping system on the rail but then again, it should be centered...

I'm rambling. It's friday and I just came from the bar...

[mark5pt56]

My understanding is that a "true" cowitness is the irons and dot being aligned together as viewed though a iron sight picture. I've never seen the point in that, defeats the advantages of the dot.

I've heard the argument, that if the dot fails, you don't have to shift your head.

I have mine with a Larue mount, so the irons are on the bottom third, dot unobstructed.

I've never seen a dot hit the same poi with the same poa as the irons when the dot is set on top of the front sight as viewed through the rear.

[Redhat]

Some good points.

But the dot, if zeroed for 300m using 25m target, should be adjusted POI 1.5cm below the targets aiming point. Lolly popping the dot to the top of the front sight post only puts you on paper. Assuming you are using the M68 with issued mount and M855.

That's what I've heard anyway.

[militarymoron]

the utility of a 'absolute/true' co-witness, IMHO, is as a sanity check to see if anything has shifted, or checking that you optic is still zeroed when you remove and replace it. the dot doesn't have to be co-zero'd with the irons to do that - you can zero the dot independantly, then check to see where it is in relation to the front sight when looking through the irons (windage should be centered, but you can be 'one dot width' above the FSP, etc).

normally, you'd never look through the irons when using the dot. i agree - it defeats the purpose. however, there have been instances where i HAVE utilized the rear aperture with the dot to sharpen it up. the sharpness of the dot depends mostly on your vision. my eyesight isn't that good, and using the small rear aperture when sighting in the dot, or for longer ranges on small targets acts like almost like a pinhole camera and sharpens up a dot that might appear a bit blur or fuzzy. for those with less than perfect vision, look at your dot, then flip up the rear sight with the small apreture and look through it again. chances are you'll see a sharper, more distinct dot.

i think the point of brett's original post was to try to get some agreement/standardization on the terms used. here are my suggestions for defining the terms:
Co-witness - the ability to view the irons sights through the tube. This applies to any height of the optic relative to the irons, as long as they can be seen. the dot can be adjusted to the irons or zero'd independantly.
Co-zero'd - i suggest discarding the terms 'absolute' or 'true' co-witness as they're confusing. this is when the dot is adjusted so it sits on top of the FSP when looking through the irons. the zero will only be valid for the distance they're both zero'd at.

[C4IGrant]

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 how I do it as well.


There seems to be a lot of debate as to whether an "absolute" co-witness (as Dick S. used to call it) is the preferred version of the co-witness.

Most of us I think prefer a bottom 1/3 co-witness simply for the reason that it keeps more of your irons out of your FOV. I think people sometimes forget that the optic is the PRIMARY sighting system and the irons are the secondary.

To make it even more interesting, I have even seen some Tier 1 weapons that did NOT co-witness at all (on purpose). The thought was that an optic that is mounted up higher allows for ones head to be more upright giving better Situational Awareness. If the optic goes down, the operator can still point shoot until he can remove the optic and go to the irons.

I have been practicing this recently, by removing my optic and just using my front sight base (no rear) to shoot human size targets out to 75yds! It is VERY easy to do and am fairly confident that I could keep someones head down at much longer distances.


C4

[DrMark]

...so after this thread, I'm picturing a Vodka ad: Absolut Co-Witness

Too bad I have no Photoshop skills.