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#1 OFFLINE   dtrax

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Posted Dec. 01 2011 - 02:14 PM

Hey guys, first post here.

I ordered an EOTech 516 and should have it by the weekend. I'd been reading a bit on co-witnessing red dot sights w/ BUIS, and was wondering your preferences.

Absolute: Red dot aligns with tip of FSP. That seems to be more useful for something like an Aimpoint with a single dot.

Lower 1/3: The base of the optic is raised so the red dot is above the FSP.

The question I have is, how do you prefer the EOTech to co-witness? The 516 is like most, with a 65 MOA ring and a 1MOA dot. I was figuring lower 1/3 will allow for more field of view which was why a went with the 516 (has a built in 7mm riser).

FWIW, I do have a Magpul MBUS rear sight (keep it flipped down for using an optic) along with a fixed FS. Well, the FS on my AR is detachable (FSB is railed) but that sorta defeats the purpose of BUIS. Right now I have a Burris AR-332 (fixed 3x) and the FSP does "disappear" a bit, but it's still noticeable and sometimes distracting. Will I have a similar issue with the EOTech?


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#2 OFFLINE   nitehawk

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Posted Dec. 01 2011 - 02:24 PM

:welcome: to the Armory..... :) Which Ar did You get... :unsure: IMHO....would not worry about the co-witness factor...once You have the Eo set up....check things out...believe You will see what I mean about the co-witness.

Enjoy the BRD..... :thumb: You are going to like that Eo..... :oh yea:


#3 OFFLINE   Pepper

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Posted Dec. 01 2011 - 02:38 PM

I use an absolute co-witness, and I like it. I understand the guys who prefer a lower 1/3, and in reality, I don't think it matters either way, it's down to what people are most comfortable with, or prefer.


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#4 OFFLINE   AGENT TIKKI

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Posted Dec. 01 2011 - 02:45 PM

Both types of cowitnesses require you to put that itty bitty 1 moa dot on the tip of the front sight post. I know its sounds counterintuitive, but that the way its supposed to go, and that's how a RDS sight works.

The reason why people like the lower 1/3 cowitness is because, if you have a fixed front sight, it will only be seen on the lower portion of your sight, takes up less space in your sight picture.


#5 ONLINE   redbarron06

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Posted Dec. 01 2011 - 03:52 PM

Both types of cowitnesses require you to put that itty bitty 1 moa dot on the tip of the front sight post. I know its sounds counterintuitive, but that the way its supposed to go, and that's how a RDS sight works.

The reason why people like the lower 1/3 cowitness is because, if you have a fixed front sight, it will only be seen on the lower portion of your sight, takes up less space in your sight picture.

No this is not how a RDS works. A RDS reguardless of the type, make or model work independently of the guns iron sights.

Zero your irons then fold them down out of the way. Then zero your dot. The sight systems are completly separate and not related. With an absolute cowitness you can set the dot to the top of the front site to start the zero process but only to start it.


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#6 OFFLINE   SSGN_Doc

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Posted Dec. 01 2011 - 05:00 PM

No this is not how a RDS works. A RDS reguardless of the type, make or model work independently of the guns iron sights.

Zero your irons then fold them down out of the way. Then zero your dot. The sight systems are completly separate and not related. With an absolute cowitness you can set the dot to the top of the front site to start the zero process but only to start it.


This^

It comes down to personal preference. I like absolute co-witness ,because my cheekweld is the same with whichever sights I'm using.

I do have a fixed front sight and it does end up having the dot of my EOTech pretty much on top of the sight post. Some folks don't want that much of their front sight in the window. It has never bothered me.


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#7 OFFLINE   AGENT TIKKI

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Posted Dec. 01 2011 - 05:18 PM

No this is not how a RDS works. A RDS reguardless of the type, make or model work independently of the guns iron sights.

Zero your irons then fold them down out of the way. Then zero your dot. The sight systems are completly separate and not related. With an absolute cowitness you can set the dot to the top of the front site to start the zero process but only to start it.



Funny thing, I do almost always do a 50-220 yard zero with my ARs. My sights are zeroed at 50.

So I zeroed my aimpoint micro with an absolute cowitness with my KAC mount.
I zeroed it by cowitnessing on my sights. Confirmed Zero at 50, took it out to 10" steel at 200 to confirm.

I decided to try out the lower 1/3 cowitness, so I removed the base from the KAC mount, added the spacers and remounted it. I cowitness'd it first and put my dot on the post. Confirmed at 50, with a few shots, I did tweek it a bit, but not much, just a couple clicks. Took it out to 200, and it confirmed it. Same Aimpoint unit, same mount, with the additional spacers.

I puzzled me to say the least that this worked for me. That is why I said it seemed counterintuitive. But this has been my experience.

I don't like sighting in 25 yards and under with red dots, as I've run into parallax issues with my other sights. I personally like the 50 yard zero more, as most of my shooting is under 300 yards.

How is it supposed to be different? Can you please explain how I've been wrong in zeroing my RDS?

Please don't take this as a challenge, I'd really like to know if I've been doing it wrong. :unsure:


#8 OFFLINE   c0nspire

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Posted Dec. 01 2011 - 05:32 PM

Tikki and Barron both express the correct concept but need some clarification: the reticle on an RDS "floats" with you. The dot is not "fixed" in place like on a regular scope. Once zeroed, the RDS will always show you point-of-impact, even if you cock your head slightly up, down, or side-to-side. This is why they are so popular - they are forgiving to the point that you can quickly put the dot on what you want to hit and still what you are aiming for, even if/when you do not have the rifle perfectly shouldered/aimed.

So... with both absolute AND lower 1/3rd, when you look through your BUIS, the red dot should be parked on top of your front sight (after all, that dot shows point-of-impact when zeroed - same as your irons). With absolute co-witness this all happens in the center of your RDS. With lower 1/3rd this all happens in the lower third of your RDS. As you indicated, most folks who like lower 1/3rd do so due to the added field-of-view, as well as a slightly more "heads-up" position they feel gives them more situational awareness.

As stated in the post above, these are two independent sighting systems. Zero your irons first. Then look through them and zero the dot to your RDS to the top of the front sight post (regardless of absolute or 1/3rd RDS positioning). This gets you "on paper" to start zeroing the RDS. Now zero the RDS and confirm (folding down your rear sight will probably make it easier and less distracting).

I used to run my EOTech XPS with absolute co-witness. Like you, I had a fixed front sight and a folding rear. I like absolute co-witness myself because I like the consistent cheek weld however, lower 1/3rd seems to be the most popular from my reading.

As for the front sight base being in your field of view: for me, the EOTech reticle was pronounced enough that I found myself not paying attention to the FSB at all. It's hard to imagine in your mind's eye, but once you see how the EOTech reticle "moves" with your eyes and the rifle, the FSB is easy to ignore. This should be even less distracting if you are running lower 1/3rd as you will se even less of the FSB.

Hope this helps!

Edited by c0nspire, Dec. 01 2011 - 05:53 PM.



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#9 ONLINE   redbarron06

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Posted Dec. 01 2011 - 05:38 PM

Funny thing, I do almost always do a 50-220 yard zero with my ARs. My sights are zeroed at 50.

So I zeroed my aimpoint micro with an absolute cowitness with my KAC mount.
I zeroed it by cowitnessing on my sights. Confirmed Zero at 50, took it out to 10" steel at 200 to confirm.

I decided to try out the lower 1/3 cowitness, so I removed the base from the KAC mount, added the spacers and remounted it. I cowitness'd it first and put my dot on the post. Confirmed at 50, with a few shots, I did tweek it a bit, but not much, just a couple clicks. Took it out to 200, and it confirmed it. Same Aimpoint unit, same mount, with the additional spacers.

I puzzled me to say the least that this worked for me. That is why I said it seemed counterintuitive. But this has been my experience.

I don't like sighting in 25 yards and under with red dots, as I've run into parallax issues with my other sights. I personally like the 50 yard zero more, as most of my shooting is under 300 yards.

How is it supposed to be different? Can you please explain how I've been wrong in zeroing my RDS?

Please don't take this as a challenge, I'd really like to know if I've been doing it wrong. :unsure:

It may very well work for you on that rifle. Nothing is wrong if it does. For me on my rifle I start at a cowitness but the dot is several inches off at 50. Once the dot is zeroed if you look through both sights the dots actually sits about 3 MOA to the left of the top of the post when zeroed.

The point is mainly that when shooting the dot forget about the FSP. The dot will work with no front sights at all. A quality dot like Aimpoint or EOTech will compensate for small differences in cheek weld. Don't ask me how but it does. The object of using a dot is to speed up rapid shots. This is done because you don't have to line up 2 reference points with the target.


#10 OFFLINE   AGENT TIKKI

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Posted Dec. 01 2011 - 05:50 PM

It may very well work for you on that rifle. Nothing is wrong if it does. For me on my rifle I start at a cowitness but the dot is several inches off at 50. Once the dot is zeroed if you look through both sights the dots actually sits about 3 MOA to the left of the top of the post when zeroed.

The point is mainly that when shooting the dot forget about the FSP. The dot will work with no front sights at all. A quality dot like Aimpoint or EOTech will compensate for small differences in cheek weld. Don't ask me how but it does. The object of using a dot is to speed up rapid shots. This is done because you don't have to line up 2 reference points with the target.




I agree with you here. RDS are fast. Just look at your target. Don't focus on your sight. Focus on your target and put your dot on your target. I love getting into the rhythm of squeezing the trigger as the dot bounces on your target. Its almost like....cheating..... :nt:


#11 OFFLINE   XJOEX

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Posted Dec. 01 2011 - 06:30 PM

If it's me we are talking about I would use lower 1/3 when I have a front sight post. Absolute when I run folding sights.


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#12 OFFLINE   Killer308

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Posted Dec. 01 2011 - 07:38 PM

I believe the 516 is set for 1/3 co witness. I think it has a 7mm riser built into the base. I'm on my phone so I can't check. I believe it's the same as the 517 but it uses different batteries. I have a 517.


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#13 ONLINE   gshayd

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Posted Dec. 01 2011 - 11:55 PM

I prefer an absolute co witness myself. Like everyone has said the red dots are pretty forgiving when it comes to cheek weld and canting the head a little unlike the irons where a consistent cheek weld is needed plus sight alignment and all that other good stuff. Plus for an old fart like me with bad eyes sometimes it harder to get a good sight picture with irons which is why I am luvin the red dot sights.


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#14 OFFLINE   Killer308

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Posted Dec. 02 2011 - 12:27 AM

Ok now that I'm home on the computer I was able to confirm that the 516 does have the 7mm riser built into the base like the 517. It will be a 1/3 co witness.


#15 OFFLINE   drck1000

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Posted Dec. 02 2011 - 07:17 AM

If it's me we are talking about I would use lower 1/3 when I have a front sight post. Absolute when I run folding sights.


That's my current theory.

My first AR has an EoTech 512 absolute co-witness with Troy BUIS. My next AR (on it's way as I type this) will have a FSB and fixed rear sight and eventually will have an Aimpoint Micro with riser for lower 1/3 co-witness. I like the EoTech with absolute co-witness and the next AR is for testing how I like it with a FSB and Aimpoint with lower 1/3 co-witness.

I haven't tried running the EoTech with the Troy BUIS up, but I don't think it would really bother me. I'll try it next time I have some range time.


#16 OFFLINE   dtrax

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Posted Dec. 02 2011 - 12:39 PM

Thanks for the replies everyone. I went with the 516, but the XPS2 was something I was also considering. I basically flipped a coin and chose the 516, but figure I can return it/sell it if I end up not wanting the riser.

The UPS truck should be here soon; can't wait to install it.

I think the issue I have currently with my Burris is that since it's 3x magnified the FSP becomes bloated and fuzzy. It was never a big deal until I recently took off my FSP and loved how much my field of view cleared up. But it seems from all of you guys' experiences I shouldn't have a problem with the EOTech. I'll probably put the Burris on a 22LR upper in the future. It's a nice optic, just not ideal for CQ stuff that I like to train for with the AR.

:welcome: to the Armory..... :) Which Ar did You get... :unsure: IMHO....would not worry about the co-witness factor...once You have the Eo set up....check things out...believe You will see what I mean about the co-witness.

Enjoy the BRD..... :thumb: You are going to like that Eo..... :oh yea:


I picked up a Rock River back in september. I've put about 800 rounds through it so far. No problems at all, except for one FTF (ammo problem, not the rifle). Awesome rifle and incredibly fun to shoot. I recently took a carbine class as well - 8 hours of rapid fire drills and technique. I qualified at the end of the class (2nd best), but I'll be taking it again for sure to hone in my skills.

The funny thing is all of my non-gun friends think I'm a loonatic for owning an AR. LOL I just explain to 'em that I like to play GI Joe's. And I'm training for the zombie apocalypse. :thumb:


#17 OFFLINE   Killer308

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Posted Dec. 02 2011 - 12:56 PM

It may very well work for you on that rifle. Nothing is wrong if it does. For me on my rifle I start at a cowitness but the dot is several inches off at 50. Once the dot is zeroed if you look through both sights the dots actually sits about 3 MOA to the left of the top of the post when zeroed.

The point is mainly that when shooting the dot forget about the FSP. The dot will work with no front sights at all. A quality dot like Aimpoint or EOTech will compensate for small differences in cheek weld. Don't ask me how but it does. The object of using a dot is to speed up rapid shots. This is done because you don't have to line up 2 reference points with the target.


I don't have iron sights on any of my rifles except my kids 10/22 which also has a scope. That is definitely the beauty of the EOTech. The dot can be anywhere in that little TV screen and you don't have to have a perfect cheek weld. I sighted mine in at 50yds just like it was a scope. I like shooting it out to 500yds quite often. (7x magnifier)


#18 OFFLINE   dtrax

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Posted Dec. 03 2011 - 12:35 AM

Received the EOTech today and installed it on my rifle before I left for work. I almost called out to head to the range to try it out, but my responsible side prevailed. :wink:

Anyways, I have a noob question. How important is consistent cheek weld with an EOTech? I ask because I noticed when I hold the rifle steady on target, if I shift my head around the reticle doesn't stay on target. I was under the impression it would - in other words, no parallax or eye relief so no matter where my head is the reticle would remain consistent. Or maybe I'm confused?! Help me understand guys!

FWIW, I really like being able to keep both eyes open. I would get mucho tunnel vision and strain using my previous scope.


#19 OFFLINE   Killer308

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Posted Dec. 03 2011 - 01:06 AM

Received the EOTech today and installed it on my rifle before I left for work. I almost called out to head to the range to try it out, but my responsible side prevailed. :wink:

Anyways, I have a noob question. How important is consistent cheek weld with an EOTech? I ask because I noticed when I hold the rifle steady on target, if I shift my head around the reticle doesn't stay on target. I was under the impression it would - in other words, no parallax or eye relief so no matter where my head is the reticle would remain consistent. Or maybe I'm confused?! Help me understand guys!

FWIW, I really like being able to keep both eyes open. I would get mucho tunnel vision and strain using my previous scope.


That's why you sight in your iron sights and the ignore the sights when you sight in the EOTech. Once the EOTech is sighted in no matter where the dot is in your sight picture as long as the dot is on target that is your point of impact for the distance it was sighted in at. With an EOTech most of the screen can be broken and unuseable but as long as there is some space for the dot to be seen it will still be accurate. The dot doesn't have to be centered in the screen. There is no parallax with an EOTech.


#20 OFFLINE   Felmac

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Posted Dec. 03 2011 - 01:49 AM

I use an absolute co-witness, and I like it. I understand the guys who prefer a lower 1/3, and in reality, I don't think it matters either way, it's down to what people are most comfortable with, or prefer.

++1 :thumb:


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