got question...

**Mity2** · October 3rd, 2009, 04:49 PM

Could someone explain to me in plain english what does "co-witness" optic set up on AR platform means?

Thanks

**d90king** · October 3rd, 2009, 04:54 PM

It allows you to use the optic in conjunction with your iron sights. I prefer lower third co personally. Depending on what mounts you use, often times you cant use your BUIS system and optic...

**Suburban** · October 3rd, 2009, 05:48 PM

Lower 1/3 co-witness. The iron sights would line-up with the dot of the optics if the photo was lined up better. Absolute co-witness would have the iron sights and dot right in the middle of the EoTech window.

Does that help?

**GuyMontag** · October 3rd, 2009, 07:15 PM

Maybe you could use a subject that is actually searchable and has meaning.

**Mity2** · October 4th, 2009, 01:39 AM

So then if I want to set up my flat top mounted optics to 1/3, You would have to raise the scope - Like EoTech would be too low if you mount them straight on to rail right?
Because otherwise dot woould be on middle of front sight post isn't it?

So if I get something like say Millet's Zoom dot or something like that, I would have to get mount like those Cantilever type ring mount they use on Aimpoint? Or do I use reguler scope ring and still be able to get 1/3 set up?

**Suburban** · October 4th, 2009, 02:19 AM

Originally Posted by Mity2

So then if I want to set up my flat top mounted optics to 1/3, You would have to raise the scope - Like EoTech would be too low if you mount them straight on to rail right?
Because otherwise dot woould be on middle of front sight post isn't it?

Yeah, you'd need a 1/2" riser or a mount specific to that optic.

Originally Posted by Mity2

So if I get something like say Millet's Zoom dot or something like that, I would have to get mount like those Cantilever type ring mount they use on Aimpoint? Or do I use reguler scope ring and still be able to get 1/3 set up?

I'm not sure about the Millet Zoom Dot, but I imagine it's got a 30mm tube like an Aimpoint. Easy way is a lower-1/3 co-witness Aimpoint mount, which are made by Larue Tactical, American Defense Manufacturing (?) (ADM), and I think Bobro/Rainier Arms.

Most of the cheaper AR-15 Aimpoint mounts will give you an absolute co-witness. A 1/2" riser (YHM or Burris) will get you close to a lower-1/3 co-witness. If you're on a tight budget, contact the guy at Primary Arms, username "Marsh1" on GlockTalk and AR15.com, or through www.primaryarms.com. I don't see the Primary Arms mounts listed separate on the website, only as an upgrade with the red dot scopes.

There's no standard with regular scope rings. One company's high rings could be similar to another company's ultra-high rings. You're on your own there. I don't think you can find a pair of rings high enough to get a lower-1/3.

**Mity2** · October 4th, 2009, 02:28 AM

Suburban, thanks for the info.

Last question - Why id 1/3 cowitness better then absolute 1/2 cowitness?

**Asmodeus6** · October 4th, 2009, 05:26 AM

Sight picture. The more irons in the dot tube the less you are going to see looking through the now obstructed tube. My dot lines up directly on the top of my FSP. (Now) As soon as it's not a brightly lit situation, you will go ... "oooOOoooooh... I see why this could be a problem." Because you can't see a damn thing.

I used 1/2" YHM risers to get the dot off the deck of the rifle and I went from top 1/3rd, to just below half. (Or directly on the very tippy top of the FSP.) I'm just using a tru-glo 30mm tube red dot and basic flip up BUIS.

This is also why flip ups are nice. If your alignment isn't bottom 1/3rd. You can get them out of the way and just use the dot with a less obstructed sight picture. However... if you go to use the irons through the dot later, say if the dot fails... the negatives of a higher co-witness immediately take effect again.