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Old 04-02-2010, 04:10 AM
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Default Absolute Co-Witness & 1/3 Co-Witiness

Absolute Co-Witness & 1/3 Co-Witiness...Whats the Difference?

So I've been on Google for the past hour trying to figure out whats the difference between the two. I've found a few answer's but It's still a little confusing for me I have an idea of what it is. How do you know if an Optic/Red Dot will be absolute Co-Witness or 1/3 Co-Witiness? I have Magpul back up sites right now and I'm going to be buying and Opitc/Red Dot this weekend and I'm not for sure what kind of Co-Witness I should be looking for. If someone can enlighten me I would greatly appreciate it

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Tyler
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Old 04-02-2010, 04:53 AM
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The mount height you choose will dictate if it is absolute or lower 1/3. The absolute co-witness will place the red dot on your front sight so you will view the sight as well as the red dot. The lower 1/3 places your sights in the lower 1/3 of the scope's field of view thus making the red dot float above the sights. Having owned both, I found the lower 1/3 type faster and easier to use but some prefer the absolute. With Magpul sights folded, it will not really make much difference.

My current favorite set up is the Aimpoint T1 or H1 with an American Defense lower 1/3 riser mount. Mounting most red dots without a riser will result in a sight too low to use. American Defense and LaRue make excellent riser mounts.

Our department used Aimpoints since the late 90s and have never had one fail even in our Alaskan extremes.

I have a couple of Bushnell red dots that mimic the H1 and the Trigicon sights. Both are mounted on 10/22s currently but are holding up fine for plinking and hunting use. I toyed with mounting the Bushnell H1 clone on my M&P15-22 but will have to research if the Bushnell can mount on a riser.

Good luck and have fun with your rifle.
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Old 04-02-2010, 04:55 AM
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My understanding is co-wit. Is where the red dot is in line with your sights... meaning if u look at your open sights they r on target and the red dot is too.. a 1/3 unless I'm mistaken means the open sights set about 1/3 of the way up in to your line of sight threw your optics... if that makes since... you may wanna look around at other peoples set up befor doing that.. the only reason for this is to have your iron sights for back up incase your optics die ..... me personaly.. I run a 3-9x42 optic with a mini reflex sight on a 45 degree mount you can seach my name for pics.. but it works well.... close up sights that need to be tapped fast I roll the rifle over and use the reflex and for the further shots I roll it back up and use the optics..
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Old 04-02-2010, 05:05 AM
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Ya what he said... cause he said it much better
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Old 04-02-2010, 09:00 AM
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Quote:
Originally Posted by idbstyler View Post
How do you know if an Optic/Red Dot will be absolute Co-Witness or 1/3 Co-Witiness? I have Magpul back up sites right now and I'm going to be buying and Opitc/Red Dot this weekend and I'm not for sure what kind of Co-Witness I should be looking for. If someone can enlighten me I would greatly appreciate it

Thanks
Tyler
Here are some options

(A) 3/4'' riser and 30mm Tasco red dot with low profile rings = AC-W

(B) 3/4' riser with 40mm BSA tube red dot = L 1/3

(C) SightMark Holosight = AC-W

(D) PEPR 30mm mount and Tasco red dot = AC-W
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Absolute Co-Witness & 1/3 Co-Witiness-dsc01849-jpg   Absolute Co-Witness & 1/3 Co-Witiness-dsc01852-jpg   Absolute Co-Witness & 1/3 Co-Witiness-dsc02253-jpg   Absolute Co-Witness & 1/3 Co-Witiness-dsc02570-jpg  
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Old 04-02-2010, 10:14 AM
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The iron sights and red dot are "co-witnessed" when they're in the same plane, meaning the dot is at the top of the front sight when looking thru the iron sights.

Since good dot sights have no parallax it makes not a twit of difference where in the optical sight the dot happens to be when looking thru the irons as long as it's at the tip of the front sight. I think the other terms are an attempt to describe just where the dot might be -- lower 1/3 of the glass, perhaps -- even though it has no effect. With cheap optics it's better to have the dot centered in the glass as much as possible.

Co-witnessing (if that's a verb) of a dot sight not aligned with the iron sights is an oxymoron. If you can't see the dot looking thru the irons the dot ain't co-witnessed.

Co-witness is not the same as coaxial. Think of a red dot (or telescopic sight) mounted on top of a M16 carrying handle. You can't see the dot (or cross hairs) looking thru the irons.

Co-witnessed:



Coaxial:



-- Chuck
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Old 04-02-2010, 10:42 AM
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Also, something that a lot of people don't realize. The dot on an aimpoint is a "floating" dot. If you mount it in a lower 1/3 co witness, it means that when using the dot, the dot will be above the irons. But, if you drop your head to look through the irons, the dot will be in sight still, right at the tip of the your front post.

Provided, of course, that they are sighhted in for the same point of aim.
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Old 04-02-2010, 10:46 AM
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Here's a sight of a "lower 1/3" co-witnessed dot I found on the web. The bullet will strike within the dot no matter where it is in the window.



The easiest way to zero the M68 or other "dot" is to just look thru your zeroed iron sights and move the dot to the tip. Done. It's never necessary to remove the irons to use the dot and folding sights are expensive gimmicks for those of us without laser designators and night vision sights.

-- Chuck

Last edited by chuck s; 04-02-2010 at 10:49 AM.
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Old 04-02-2010, 11:47 AM
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As chuck above said, even a mount using a lower 1/3 witness, if your irons are sighted in, adjust the dot to the irons and it will be on target.

Examples...

This is a sight picture using the Aimpoint T-1 as the primary sight. I left the front sight deployed to give a picture of what lower 1/3 looks like...


This is the same mount, with rear and front deployed, and looking through the iron sights. Note that the dot lines up with the irons still, as they are both sighted the same.



This is the Aimpoint T-1 in a ADM lower 1/3 mount..


and a Millet DMS-1 in a ADM recon, that is absolute. You can kind of get an idea on the height difference...



Both work, but with the Magpul ACS stock, for the pure dot sight, I REALLY like the higher mount. In the past, I preferred the absolute co-witness, but after using this, I'll be staying with it.
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Old 04-02-2010, 02:26 PM
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Wow! Thanks for all the input. This was very helpful and now I know what I'm looking for. I'll post some pics of what ever I get this weekend. Thanks again!
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Old 08-11-2017, 04:13 PM
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Default Co-Witness Diagram

Here is a diagram I found that helped me understand Absolute and 1/3 Co-witness...
This diagram is similar to the photos posted above.
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Old 08-11-2017, 04:54 PM
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The OP asked his question over 7 years ago...
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