I've heard of this being done to sights, what does this mean?

On a flat top for example when you pop up your back up site and look through to the front site you see your red dot resting on the front post.Even when the rear is folded down the red dot will rest on the front post.That is the red dot co witnessed to the front sight.Thats why even when you have an A2 upper there are mounts like a goose neck mount so you can mount your aimpoint in between the rear and front sight.

Here's my AR with a PRI flip front sight and ARMS 40 rear sight and an EOtech in between.  You can see that it will all line up.  Ring in ring in ring.

Hummmmmmmm. Read that it was being able to use your iron sights to see target under your scope.
to wit: sight your scope on target, use iron sight to prove.

Quoted: Hummmmmmmm. Read that it was being able to use your iron sights to see target under through your scope. to wit: sight your scope on target, use iron sight to prove.

Fixed it

Co-witness is a fancy-schmancy term for lining everything up so that you can see your front and rear iron sights right through a non-magnified optical device; almost always some form of electronic red-dot.

Years ago, when I was a flight instructor, I was forced to the conclusion that individuals vary tremendously in how they sort out optical data. And that one set method of teaching would not work for everyone, or for even 50% of the student population. I have since been forced to the conclusion that this holds just as true for rifles as it does for aircraft. Perhaps somebody like Bartholomew Roberts who understands optics could explain why this is; although I suspect the reasons are as much psychological as they are optical.

In any event, it appears that any one individual will react to co-witnessing in one of three ways.

There are those guys who can instantly sort through almost any amount of optical clutter. They can have their front and rear iron sights right in the main sight plane of their red dot scope and never have a problem. In fact, they’ll tell you that they don’t even see the irons when they’re shooting under pressure. These guys have the best of all situations. They can go from scope to irons with effectively zero transition time.

Other guys cannot tolerate any optical interference in the scope picture without having to carefully orient each shot. Their only salvation lies in fold-down front and rear iron sights. Their transition time from scope to irons can get to be pretty lengthy, particularly when the clock is running or the bullets are flying.

The third group (the one I’m in) can operate well enough with a limited amount of extraneous stuff in the scope picture. We can either go conventional height on the scope; coupled with a fixed front and fold-down rear or in the alternative, fixed front and rear irons with the scope raised just enough to place the irons below the primary scope sight plane. This requires some transition time from scope to irons but, a lot less than the two-fold-down set up. (Side note: Not being able to get a proper cheek weld with a raised red-dot means jack squat. You have no need for a cheek weld with a zero parallax optic.)

The main thing to understand here is that nobody else’s opinion, mine included, means jack squat as to what will work best for you. The only way to know before committing to purchase/build is to beg, borrow or steal an example of each set up and try it.

Luck,

SD

Alrighty, that's what I thought. The fancy terminology threw me off a bit though.

Perhaps I'll be grabbing a Bushnell Holosight and CO-WITNESS it with my irons.

My only question would be does anyone know if it will line up properly if the Holosight is mounted on the top of the front handguard with a weaver rail attached to it? I have an A2 sight so this would be the only way to do it.

Here is a graphic representation of Co-witness (courtesy of the AR15.com BUIS FAQ):

+1 SailorDude

I first tried out a friends co-witnessed EOTECH and hated it, then I shot an AimPoint and loved it.  They basically do the exact same thing (red dot), but for some reason I just couldn't get comfortable with the  EOTECH set up.  My friend did say that it took him a little while to get used to the EOTECH, so with a little use I may have changed my opinion.  The best advice is shoot a rifle with that set up BEFORE you buy (they aren't cheap!!)...

______________________________________________________________

Eagles may fly, but weasels don’t get sucked into jet engines!