AR15.Com Archives
 EOTech 516 vs 512
bp805  [Member]
12/7/2009 9:10:07 PM EST
I am looking into buying my first EOTech. Originally I was looking at the 512 model because it seemed like the most basic and inexpensive option. However, I am now going to put a BUIS on my rifle and have come across the problem of accessing the buttons on the back of the sight and having enough room on the rail to mount it without having it hang too far over the end of the rail. I know the 516 might be more convenient in this aspect because the buttons are on the side and can be mounted closer to the back up sight, however the length is essentially the same (.1" longer than the 512 according to EOTech's website). Can anyone give me some opinions comparing the two?

Also, if Im not mistaken, the 516 has a 7mm riser and the 512 doesnt. What is the benefit of having a 7mm riser? I saw in another post that it will create a "lower 1/3 cowitness"? (something like that, cant remember). I know what a cowitness means, but not sure about the 1/3 lower part. Any help would be appreciated on these several topics. Thanks!
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Chairborne  [Team Member]
12/7/2009 9:17:26 PM EST
I'm personally not a fan of the lower 1/3 co-witness. If you're going to pay retail for a new EoTech I'd recommend the XPS2/3. They are much shorter than the AA versions, and have a super long battery life.

ETA: The XPS2 has a lower MSRP than the 512 or 517 (don't see the 516 on the eotech site). Can you tell I want one?
bp805  [Member]
12/7/2009 9:59:00 PM EST
What exactly does the lower 1/3 cowitness mean exactly?
Chairborne  [Team Member]
12/7/2009 10:02:21 PM EST

Originally Posted By bp805:
What exactly does the lower 1/3 cowitness mean exactly?

A normal eotech with no riser or other extraneous bullshit will co-witness exactly with your iron sights. In other words the 1moa dot will be exactly on the top of your front sight post. Some people prefer a "lower third co-witness" which means the iron sights will be in the lower third of the eotech's window. In reality most risers give a cowitness right at the ragged lower edge of the window, and it's pretty much useless IMO. Why people would pay more for such a riser/mount I don't know.
thatjonguy  [Team Member]
12/8/2009 12:51:11 AM EST
Originally Posted By Chairborne:
I'm personally not a fan of the lower 1/3 co-witness. If you're going to pay retail for a new EoTech I'd recommend the XPS2/3. They are much shorter than the AA versions, and have a super long battery life.

ETA: The XPS2 has a lower MSRP than the 512 or 517 (don't see the 516 on the eotech site). Can you tell I want one?


As soon a Larue starts stocking them, I am going to order one.
PC-Tech  [Member]
12/8/2009 4:48:31 AM EST
Originally Posted By Chairborne:

Originally Posted By bp805:
What exactly does the lower 1/3 cowitness mean exactly?

A normal eotech with no riser or other extraneous bullshit will co-witness exactly with your iron sights. In other words the 1moa dot will be exactly on the top of your front sight post. Some people prefer a "lower third co-witness" which means the iron sights will be in the lower third of the eotech's window. In reality most risers give a cowitness right at the ragged lower edge of the window, and it's pretty much useless IMO. Why people would pay more for such a riser/mount I don't know.



Here's my 517. Dot still lines up wit the site, just in the lower 1/3 of the window.
Bizzarolibe  [Member]
12/8/2009 4:56:20 AM EST
Originally Posted By bp805:
What exactly does the lower 1/3 cowitness mean exactly?


In practical terms, it means that the front sight post sits lower in your viewing window than abosolute co-witness (basically). Having owned both aboslute co-witness sights and 1/3, I prefer the 1/3. Just my preference.

Also, the XPS's only have a little more than half the battery life of the 516. As for the difference between the 516 and 512, the 516 has a 7mm riser built in (for 1/3 co-witness), has buttons on the side, uses CR123 lithium batteries, and has a cantilever base (part of the base is cut out), so it can hang way off your optics rail without hitting your handguard retainer ring. This gives you alot more room on your optics rail. It's very important if you want to add a magnifier.
Chairborne  [Team Member]
12/8/2009 9:21:50 AM EST

Originally Posted By Bizzarolibe:
Originally Posted By bp805:
What exactly does the lower 1/3 cowitness mean exactly?


In practical terms, it means that the front sight post sits lower in your viewing window than abosolute co-witness (basically). Having owned both aboslute co-witness sights and 1/3, I prefer the 1/3. Just my preference.

Also, the XPS's only have a little more than half the battery life of the 516. As for the difference between the 516 and 512, the 516 has a 7mm riser built in (for 1/3 co-witness), has buttons on the side, uses CR123 lithium batteries, and has a cantilever base (part of the base is cut out), so it can hang way off your optics rail without hitting your handguard retainer ring. This gives you alot more room on your optics rail. It's very important if you want to add a magnifier.
Of course the 516 has a longer battery life, it has two batteries vs one in the XPS sights. It's also much longer, necessitating the side buttons to use it if you have BUIS or a magnifier behind it. The battery compartment on the XPS sights is much more rugged and simple than the overly complex design used on legacy sights as well. I'd like a sight with the option for a lower 1/3 cw (like every single other eotech sight) and not one that can't be used with an absolute cowitness, but that's just me. The XPS sights have a cantilevered batt. compartment too, it's also more than an inch shorter.



3.75" / 600 hours



5.1" / 1000 hours

bp805  [Member]
12/8/2009 10:26:11 AM EST
Originally Posted By Chairborne:

Originally Posted By bp805:
What exactly does the lower 1/3 cowitness mean exactly?

A normal eotech with no riser or other extraneous bullshit will co-witness exactly with your iron sights. In other words the 1moa dot will be exactly on the top of your front sight post. Some people prefer a "lower third co-witness" which means the iron sights will be in the lower third of the eotech's window. In reality most risers give a cowitness right at the ragged lower edge of the window, and it's pretty much useless IMO. Why people would pay more for such a riser/mount I don't know.


So what is the point to having it so low in the window then? From the above picture it seems very low. Does EOTech make a sight that is the size of the 516 with buttons on the side, but without the 7mm riser?
SuperSet72  [Team Member]
12/8/2009 10:43:48 AM EST
No, all EOTechs with side buttons have internal 7mm risers, thereby enabling lower 1/3 cowitness. I prefer this to absolute cowitness. One benefit of lower 1/3 cowitness is that since the sight is not as cluttered, I can more clearly focus in on the 1MOA dot when shooting long range. When using absolute cowitness, you're negating the advantage of that dot since you're aiming using the iron sights again.
bp805  [Member]
12/8/2009 11:06:21 AM EST
Originally Posted By SuperSet72:
No, all EOTechs with side buttons have internal 7mm risers, thereby enabling lower 1/3 cowitness. I prefer this to absolute cowitness. One benefit of lower 1/3 cowitness is that since the sight is not as cluttered, I can more clearly focus in on the 1MOA dot when shooting long range. When using absolute cowitness, you're negating the advantage of that dot since you're aiming using the iron sights again.


Most of the shooting I will be doing will be inside 50 yards (I assume) and most likely wont be making long range shots. Not sure if I am worried about the window being cluttered by the front iron sight or not.
OlCrow  [Team Member]
12/8/2009 11:22:46 AM EST
I have a 512 and Troy BIUS on mine and have plenty of room between the BUIS and 512 for access to the buttons. There's about and inch and a half space. No chance of accidently hitting one of the buttons with this setup.
bp805  [Member]
12/8/2009 11:35:45 AM EST
Originally Posted By OlCrow:
I have a 512 and Troy BIUS on mine and have plenty of room between the BUIS and 512 for access to the buttons. There's about and inch and a half space. No chance of accidently hitting one of the buttons with this setup.


How far does the 512 hang off the end of the rail over the handguard?
OlCrow  [Team Member]
12/8/2009 11:35:52 AM EST
Here, I took a few quick pics for you.



OlCrow  [Team Member]
12/8/2009 11:38:48 AM EST
If you have M4 handguards it might be a problem...CAR handguards or a railed forearm is no problem.
bp805  [Member]
12/8/2009 11:43:45 AM EST
Thanks for the pictures. Looks like a good set up. I dont have a handguard with a rail on top for mounting anything so I am a little concerned with having the sight hang over the end of the rail too much if I need to leave alot of room to be able to access the buttons on the back. Might have to look into the XPS models. Anyone have pictures of that set up?
OlCrow  [Team Member]
12/8/2009 11:52:53 AM EST
Just to be clear, none of EOTech mount is off of the upper, just the battery compartment.
CSGunWorkscom  [Dealer]
12/8/2009 1:32:41 PM EST
The 512 do co-witness nice but I'm not a big fan of co-witnessing I prefer to have the buttons to on the side but with that said I really like the size of the EoTech XPS’s.

Mike @ CS TACTICAL.com
CS Gunworks is now CS TACTICAL.com
www.cstactical.com
mike@cstactical.com

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