OK.............
A friend and I were talking today about co-witnessing with Eotech's.

I swear I've shot an AR with an Eotcch mounted on the flattop, that had an ARMS BUIS mounted on the same flattop and I could co-witness right through the Eotech's window.

IF this is the case why when I go to an ARMS SIR do I have to get the bi-level SIR to be able to co-witness with an Eotech?

Can't I just use the flattop SIR?

Why am I so confused?

I think I need a nap!

PICTURES ???

Well, I can tell you that a EO Tech mounted directly to the receiver rails will co-witness with an ARMS #40 BUIS also mounted directly to the rail. That's exactly how mine is set up right now.

Since the top rail on the ARMS SIR attaches to the receiver, mounting an EO Tech on the SIR's top rail will place it's reticule above the front sight post UNLESS you have a bi-level SIR. Mounting the EO Tech as far forward as possible makes the EO Tech better anyway (reticule is clearer and your have a better FOV). I have my EO Tech mounted on the top RIS rail and there are only 4 rail slots in front of it. I'd mount it all the way forward but then I wouldn't be able to reach the buttons while shouldering the rifle.

AFAIK, if you have a SIR on your AR, the ARMS #40 is still mounted on the receiver's rail (at the very end) so it will line up correctly with the front sight post. But, if you can see the front sight post through the EO Tech's window, it really doesn't matter.

That's correct.  Here's a fixed BUIS (chopped CH) for example.  Same concept with a #40 though.

[img]http://photos.ar15.com/ImageGallery/IG_LoadImage.asp?iImageUnq=12915[/img]



As I understand it, the standard SIR rail is too high (or should I say the Eotech needs a better/modular mount).  You'll need to mount the Eotech on the lower bi-level to cowitness.



I don't believe so.  At least not to cowitness.



Because there's so much great stuff out there for AR's!!  They're truly the swiss army knife of rifles.  [:)]



Me too.    The lawn can wait.

PICTURES ???

View Quote

Not with an ARMS #40, but....

HTH

EDITED b/c I didn't spell "quote" correct and screwed up the code.

Also, I believe, as posted by Matt, that you won't be able to see the front sight post through the Eotech screen if it's on the standard SIR rail.  It's really not about "placing the reticle above the front sight post," as that can be adjusted when sighting in.  But the lower body of the Eotech blocks the view of the front sight post.

One of my main complaints about the Eotech is its built in mount.  Sure, it saves $100 on the initial purchases price, but it's not worth that savings in the long run.

The standard mount puts the front sight post directly in the middle of the Eotech screen.  I'd much prefer the front sight post to be in the lower 1/3 of the screen, leaving the top 2/3 clear for use (as well as a slightly more "heads up" position on the rifle).

Here's an example of my fixed BUIS's cowitnessing through the lower 1/3 of an Aimpoint M2.  Mount is ARMS #22 M68 with full spacer (recently switched to new extended cantilever spacer, but it's the same height).

[img]http://photos.ar15.com/WS_Content/ImageGallery/IG_LoadImage.asp?iImageUnq=1810[/img]

[IMG]http://urbansniper.150m.com/armory/eoreticle01.JPG[/IMG]

Pic courtesy of Unicorn.

Lumpy:

Thanks for posting that Eotech pic.

I really think a forward mounted Eotech on a bi-level SIR would be a sweet setup.

Still, I wish that there was a little spacer that could be installed to raise the Eotech slightly (don't have the measurements in front of me as I don't have an Eotech any more).  I'd love an Eotech with fixed BUIS's in the lower 1/3 of the screen.  [:(]

Pictures are worth a thousand words.

This is the EOTech on the SIR top rail, as you can see the EOTech sits too high on the top rail.
[img]http://www.thermaldynamics.com/pictures/SIR/10.jpg[/img]

Here is another picture with an Aimpoint as reference.
[img]http://www.thermaldynamics.com/pictures/guns/EOTech.jpg[/img]

This si the #50 bi-level SIR this allow co-witnessing with the EOTEch.
[img]http://www.thermaldynamics.com/pictures/SIR/2.jpg[/img]

And a reference picture with Aimpoint
[img]http://www.thermaldynamics.com/pictures/SIR/3.jpg[/img]

I hope this helps you clear things up somewhat.

Ok I'm with ya so far. This is what I thought. I could have sworn I shot an AR configured exactly this way.




DING! DING! DING! DING! DING! DING! DING! DING!

That's it! When I was talking to my buddy the other day on the phone I could not think of the reason why. This is it, the extra height that the ARMS rail adds to the top of the flattop.

Thank you so much!

I must have brain farted.......