Red Dot Mount/ Co-Witness ?????

[Mike J]

So I got a Bushnell TRS-25 for Christmas. I want to put it on the AR-15 I assembled from PSA parts last summer. My rifle has a fixed F marked front sight. The mount that came with the red dot is way too low. I am looking at mounts. From what I can tell if I go with a medium riser it will give me absolute co-witness. If I go with a high one it will make it lower 1/3. I understand the difference between the 2 and am thinking about going with absolute co-witness. Is there any reason lower 1/3 would work better. Also any mount suggestions are welcome.

 

[rogerjames]

If you go with absolute co-witness, the top of your front iron sight will be right where your dot is when you look through the sight. In other words, you won't have as clear a sight of your dot with an absolute cowitness. This is why many prefer the lower 1/3 set up.

 

[Inebriated]

I prefer lower-1/3. I use fixed sights as well, A2 FSB and LaRue rear. With an absolute cowitness mount, I would essentially have to look through the rear sight to get the dot, and even if I had a flip-up rear, I'd still have the front sight post right there. With the 1/3, I can just look over the sights and get a nice clear view. If the dot fails, all I have to do is get move my head, and I've got my sights... no reaching up and flipping the sights up. If the dot fogs or otherwise impedes my view of my front sight, I just have to remove it (I use a LaRue LT660 QD mount) and keep on doing what I'm doing.

Absolute cowitness makes sense for guys that have flip-up sights, and don't have their front sight post to contend with.

 

[Fast Frank]

I am opposed to the idea of "Co Witness", and here's why:

The very idea behind the red dots and holo sights is that there is no need to carefully line up the sight picture. There is no need for a repeatable cheek weld. There is no need to get the front sight positioned just so in relation to the rear sight. There is no need to remember to keep your eye focused on the front sight. There is no blurring of the target because your eye is on the front sight.

These facts are the reason why these sights are known for being much quicker to use, and make going from one target to another much faster.

Of course, doing this requires some learning. We have to train ourselves to look at the target instead of the sight.

It's done in a different way, too.

With iron sights we start by getting our rifle positioned just so, and our "Cheek weld" just right. Then, we adjust our head position until the sights align just right. After that, we move our head and the rifle as a unit to the target.

With a dot/holo sight, we hold the rifle muzzle down and look directly at the target.

without moving our eyes off the target (Yes, EYES. Shoot the dot sight two eyes open), we raise the weapon up until the red dot appears before us.

The dot is the shot. look at the target. Put the dot on the target and fire.

making the dot sit on top of the iron sights makes me revert back to iron sight use . When I see the iron sights, I automatically waste a bunch of time aligning and cheek welding. I can't help it, it's decades of training and it won't go away.

I shoot a holo sight FAR better if the iron sights are not in the picture.

I recommend lower 1/3 for this reason.

 

[Inebriated]

You can still use a red dot with 100% effectiveness with an occluded view through the optic. Left eye sees the target and directs focus to it, right eye sees the dot. This worked on older styles of optics (collimator sights I believe is what they're called), it works with Aimpoint's PRO caps that have a black front and clear rear, and are intended to be shot with both caps closed, and it's also the same general concept behind the Bindon Aiming Concept, though the BAC is intended to be used with magnified optics.

So having a front sight post directly in front of the dot, though less preferable to your view through the optic being either a completely covered and contrast-free (such as with the Aimpoint PRO's caps) or completely clear (such as with a dot with sights flipped down), it's still plenty usable.

So while you work better with nothing in view but the dot, it is not an impossible, or even particularly bothersome task to use a dot with items in front of it.

On two AK's I have Aimpoint Micros on Ultimak rails, which does allow a lower-1/3 cowitness, but I go thumb-over-bore, which puts my thumb right in front of the dot. The same concepts apply to that setup, in that my left eye sees the target, my right eye sees the dot.

But that has little to do with cowitness, I just thought it was worth mentioning.

 

[Gordon]

And expanding on the above I have found the Bindon aiming principal to produce different groups shifts when going between an occluded optic and a clear thru optic . I have tried the Bindon optics since the late 70s and found they lack for me beyond point and shoot distances.

 

[OpticsPlanet]

I've read of issues with a few of the TRS-25 and lower 1/3 cowitness - apparently some were manufactured with the diode at the 6 o'clock position, instead of the 4 o'clock position, and causes problems with viewing the irons.

Examples are shown at arfcom:

http://209.251.48.101/forums/t_3_18/625347_Bushnell_TRS_25_Hirise_model__Need_help_.html

Just something to be aware of.

Mark H.

 

[Winkman822]

I agree with FastFrank above. The point of a red dot or holographic sight is to simplify not complicate the aiming process. I have an EOTech on my AR15 and have back up iron sights that flip up in the event my EOTech goes down for some reason. If my EOTech is operating properly, the irons are folded down. If the EOTech isn't operating properly for some reason, the irons will be flipped up and I'll simply look through the blank glass of the optic.

Granted, after either your irons or your optic is zeroed, you can cowitness to roughly zero the other (i.e. if your irons are properly zeroed for a given distance, you get a new red dot, you can roughly zero it by co-witness aligning the red dot to the properly zeroed irons, and vice versa if you have a properly zeroed red dot and throw on new/different irons).

 

[Mike C2]

I am in agreement with Winkman. I have my Eotech setup to absolute co-witness and use a Magpul MOE rear sight and a Yankhee Hill gas block with built in flip up sight.

You can double check the red dot by flipping up the "irons" and see if they align. Then fold back down and continue to use optic until time that it has a problem or you want to verify again.

 

[rogerjames]

Well the OP has a fixed front sight so he can't very well flip that down, so his two options are an absolute or lower 1/3 co-witness.

 

[txgunsuscg]

I personally run lower 1/3 on both my rifles. I have fixed front sights and folding rear which I run always up unless my magnifier is present. The only time I actually use both (red dot and irons) at the same time is zeroing. I like lower 1/3 because my sights are easily available, but not in the way, and especially with the magnifier, I don't feel like my irons interfere with my use of the dot. Also, the majority of my rifle training was based on the premise that I would be operating in CBRN gear a lot, and the higher optic height worked better with the mask. Probably not something you're worried about, but some people are. Just my $.02.

 

[David4516]

Check this out:

http://www.amazon.com/Alamo-Four-Star-DLOC-TRS25-Standard/dp/B00HHG6YYG

It's one of the more expensive options but looks like a nice mount.

I'm thinking about upgrading to a TRS-25, with that mount. My AR-15 currently wears a very cheap BSA sight (I think it was like $25.00 when it was new and I got it second hand). I also have a cheap UTG quick-detach riser mount for it. One thing I can say though, that impresses me, is even with my super cheap setup, I can detach and then re-attach that red dot and it retains it's zero really well...

I do have some pretty good back up sights however (Matech, I think the military uses the same sight)

 

[MachIVshooter]

IMO:

Lower 1/3 with a fixed front sight, since the front sight will always be there.

Absolute with front & rear folding sights, because they'll be out of the way when folded, but in a more useful position when up.

 

[strambo]

All co-witnessing means is that it is possible to see the irons through the optic (somewhere), that's it. It doesn't mean you are using the irons and the optic at the same time which would be bad form and a waste of time (and a confusing mess).

With a functioning RDS, even with an absolute co-witness and a fixed rear iron sight, you still would ignore the rear iron and only focus on the dot regardless of cheek weld and where the dot is positioned in the lens. If the dot is on target, but in the top left corner of the lens, squeeze the trigger, irons play no role whether they are seen/noticed/aligned or not.

 

[henschman]

I always prefer an absolute co-witness when I have a folding rear sight. Cheek weld makes me faster on target... bring that rifle up to the old familiar place on your face and there the dot is, right in the center of your FOV. It is also more stable and involves less muscle than an unsupported head. You won't always have a large, close target... fundamentals like cheek weld are important when you have to take that shot on a smaller or longer ranged target. Basically there is no downside to having a cheek weld, but there is plenty of downside to not having one. I never even notice the FSB when I am shooting fast with an absolute co-witnessed dot. It's like it disappears.