I noticed that LaRue lists the lower 1/3 cowitness as "proper" in their product descriptions, and am trying to understand why this is the case.  I am curious as to why the lower 1/3 is advertised as "proper," and the reasoning behind why some (including the well respected company LaRue) consider it to be the superior option.



1.) Doesn't the absolute cowitness allow one to use both iron sights and the optic as zero confirmations for each other?  That is to say, simply looking through the irons will allow the user to confirm that the optic zero has not wandered, and looking through the optic allows confirmation that the iron sights are still zeroed, correct?  This seems to be a very worthwhile option to have.  Is this not the case?


2.) With absolute cowitness, one is able to use the same cheek weld with both irons and optic.  Doesn't the lower 1/3 cowitness require that muscle memory for two different cheek welds be learned?  Wouldn't the absolute cowitness also be superior in this regard?


It seems that the only thing that lower 1/3 cowitness has going for it is a (slightly) less cluttered field of view, but is this worth it if you lose the above two advantages of absolute?

With a lower 1/3 cowitness you can still zero the optic (assuming it is parallax free like EOTech and Aimpoint) by lowering your head slightly to position the red dot in the sight plane of the irons.

The rest of your post is pretty much spot on.  I think the only real advantage of the lower 1/3 is less clutter in the FOV.

But, for me, that is the better of the two options.

Other than aiding you in quickly sighting in either the irons or red dot sight when one of them is already zeroed, there seems to be a lot of emphasis placed on what is essentially a happenstance and a convenience.

Cluttered view?  Since you can use the red dot regardless of where it is in the sight picture, I hope you're not lining up your irons, red dot and target before shooting.  When I use the Aimpoint or EOTech with iron sights already in place, the irons are ignored.

No co-witnessing for magnified optics, we've got along just fine

Quoted: Cluttered view?  Since you can use the red dot regardless of where it is in the sight picture, I hope you're not lining up your irons, red dot and target before shooting.  When I use the Aimpoint or EOTech with iron sights already in place, the irons are ignored. No co-witnessing for magnified optics, we've got along just fine

Don't know if this was directed at the OP or me, but I have flip up front & rear BUIS on my primary rifle, and even if I didn't I would know to overlook the irons

Another reason I like the lower 1/3 is it gives me a better cheek weld and a more natural pointing stance/shoulder mount of the weapon.


As always, YMMV

As already stated, you can still verify zero of irons and dot with an eo or aimpoint using a lower 1/3 (the dot stays on target wherever it is in the tube).

The muscle memory idea can be debated, but is not a problem for me.

The red dot is the primary sight and the lower 1/3 cowitness makes it less cluttered and therefore easier to acquire (this is the idea).

If you need your irons for an out of the ordinary situation, they are there.  For all other situations you don't need irons.

I like the more heads up posture the lower 1/3 gives me with an aimpoint.
I don't like losing the dot for a split second in front of the rear aperture.  The lower 1/3 makes this hard to do for me.

When using the Aimpoint or whatever other sight you choose, you're probably going to be looking over your iron sights.  With a lower 1/3 cowitness, you'll be looking through the center of the sight instead of the top half.  

Quoted: Quoted: Cluttered view?  Since you can use the red dot regardless of where it is in the sight picture, I hope you're not lining up your irons, red dot and target before shooting.  When I use the Aimpoint or EOTech with iron sights already in place, the irons are ignored. No co-witnessing for magnified optics, we've got along just fine Don't know if this was directed at the OP or me, but I have flip up front & rear BUIS on my primary rifle, and even if I didn't I would know to overlook the irons Another reason I like the lower 1/3 is it gives me a better cheek weld and a more natural pointing stance/shoulder mount of the weapon. As always, YMMV

It was directed at the OP.  Many folks post shots of the Aimpoint sight pictures and dot with the irons fully lined up, I can see how this may lead new shooters to believe that's how these sights are supposed to be used, hell I took a picture or two just like that.  I prefer a clean sight picture with no irons in it at all, but fixed irons do have their advantages and I can't say anything negative about them.

Thanks for the replies.


There were some good points made, and after further consideration, I have come to agree with LaRue that Lower 1/3 Cowitness is "proper," and here is why:

My original questions...

Quoted: 1.) Doesn't the absolute cowitness allow one to use both iron sights and the optic as zero confirmations for each other?  That is to say, simply looking through the irons will allow the user to confirm that the optic zero has not wandered, and looking through the optic allows confirmation that the iron sights are still zeroed, correct?  This seems to be a very worthwhile option to have.  Is this not the case?

Since the dot can be anywhere in the field of view, this is a mute point.  The Lower 1/3 and Absolute are equal in this regard.

Quoted: 2.) With absolute cowitness, one is able to use the same cheek weld with both irons and optic.  Doesn't the lower 1/3 cowitness require that muscle memory for two different cheek welds be learned?  Wouldn't the absolute cowitness also be superior in this regard?

For a 30mm optic, the difference in height between the two types of cowitness is 0.197".  This may not be enough to be significant.

For a 20mm optic, the difference between the two is 0.131".  Even less significant.

Quoted: It seems that the only thing that lower 1/3 cowitness has going for it is a (slightly) less cluttered field of view....

Since my interest is mainly directed toward the Aimpoint Micro T-1 with its small 20mm lens, Lower 1/3 is more valuable (in terms of less clutter) relative to 30mm optics.

Can someone explain to me how you can zero a Micro T1 using the iron sights. If your irons are in the lower 1/3rd of the tube wouldnt your dot be very low in the tube picture?

I use a 1/3 co-witness with an eotech.  The difference between looking through the sights or using the EO tech is all about moving my head about 1/4".  I don't think this will harm muscle memory.  

I "absolute" - rear is a troy buis and when it is down position never see the front sight through my eotech

had it both ways several times to try - both are good but like the eotech direct on flat top

an added benefit is point is closer to barrel bore