What's so good about 1/3 co-witness?

[Boiler74]

The school of thought I subscribed to when buying my mount from Larue was this:

If you have flip-up sights (front and back sight), you get absolute co-witness. If you drop a grand on an aimpoint/eotech/etc. with mount, you don't want your BUIS in the way unless you need it. And if you do need em, you flip em up and they are in the middle of the tube. GTG

If you have fixed sights, get 1/3. That way they are out of the way of the red dot and any possible ballistic drop compensators. And then if you need em, you just drop your head a little. This is what I ended up with b/c my DD carbine has a fixed front sight. And I like it.

This is just the reasoning I found when researching this issue, and I agree with it.

 

[jblomenberg16]

I think what Esrice's illustrations show is that you can still co-witness in the lower 1/3 of the tube and have the irons in the same plane as the optic. That means no difference in cheek weld.

 

[RichardR]

I think what Esrice's illustrations show is that you can still co-witness in the lower 1/3 of the tube and have the irons in the same plane as the optic. That means no difference in cheek weld.

The purpose of 1/3 co-witness is to get the front sight post out of the sight picture seen within the optic, the shooter has to change their cheek-weld in order to make that happen.

In other words, yea while you don't have to change your cheek-weld, but by not changing your cheek-weld in order to get the front sight out of your optic's sight picture there is no reason to go with a 1/3 co-witness set up in the first place.

 

[MTC]

I've used a red-dot sight and a trijicon optic with a triangle reticle. If I don't concentrate too hard (if I'm not thinking too much about what I'm doing), two eyes open seems to work OK in good light. If I try to concentrate too much, I get "ghosting" and have trouble focussing on the reticle/target. Does that sound like it's the same as what you're dealing with?

Possibly. Unable to answer with certainty without additional testing.

 

[esrice]

The only thing more difficult than understanding co-witnessing is explaining it in writing.

To MTC and Blackhawk2001-- guys keep in mind that, in regards to both-eyes-open shooting, red dot sights are used differently than your pistol sights.

Unlike pistol shooting, your main focus is on the target when using a red dot sight. When your rifle is shouldered, you get a good cheek weld and look down through the sight, at the target, with both eyes open. When you do this, you will see the sight body magically "disappear", and you will be left seeing only your target with a red dot superimposed on it. It will look the exact same as if you had a red laser mounted somewhere on your gun, and it was shining a dot on the actual target. The only difference is that the target can't see the dot on him.

I'm not a optometrist, but the way I understand it is that your two eyes are seeing two different pictures, and then working together to make those form a single image (which is what your eyes are doing all the time anyway). So (assuming a right-handed shooter), your right eye is looking down through the tube and seeing the dot and the target. Your left eye is looking down the outside of the optic, gathering peripheral information, and looking at the target. Your right eye sends a message to your left eye, allowing it to also see the red dot.

Don't believe me? Try this:

MAKE SURE YOUR RIFLE IS UNLOADED!

AGAIN, MAKE SURE YOUR RIFLE IS UNLOADED!

Shoulder your rifle, pointing it in a safe direction.

Turn on your optic.

Open the rear lens cap, but CLOSE the front lens cap, making it impossible for your right eye to see the target though it.

Keeping both eyes open, aim at something.

You'll be amazed when you realize that your eyes are sending signals back and forth, and that you can still get an entire sight picture, even with the front lens cap blocked. You could shoot that way just fine and make hits.

Now, as for co-witnessing, lemme think on this and see if I can figure out a way to explaining it clearly. Maybe if I wait long enough shooter521 will have beat me to it. . . .

 

[MTC]

... guys keep in mind that, in regards to both-eyes-open shooting, red dot sights are used differently than your pistol sights.../snipped for brevity/

That's about as good as can be expected for a written explanation, and helps to address the "peripheral" issue. I guess there are a few things that can be reviewed or gone over again before another course or trip to the range.

The only thing more difficult than understanding co-witnessing is explaining it in writing.

Yeah, it may be unrealistic to expect someone to explain that adequately through this medium. It could likely be resolved in a few minutes at the range with some butcher paper or paper target and a marker, and it would seem more appropriate anyway, since that's where it needs to be tested and verified.

Thanks again.

 

[jblomenberg16]

Just got my rifle out and checked a couple things. I tried to take some pictures but couldn't get my camera to really focus on what I wanted it to do give a good visual of the co-witness.

First, my Aimpoint is in a LaRue mount that affords the lower 1/3 co-witness. I'm using YHM front and rear flip ups.

After quadrupal checking my gun was unloaded, I went to the basement and tried a couple of things.

1) My normal shooting position with nose to charging handle, with dot "on" and sights stowed. The result was that the dot appears to be in the center or just a little below center of the ghost ring of the optic.


2) Same as above, and I did the test that esrice mentioned with the front flip cap close. Pretty cool the way the eyes works!! I was almost right on my POI even with the cap closed.


3) Flip the front sight up, where it would be the same hight as a normal fixed front sight. This tricked my eyes a bit and I could align it either on top of the post in the bottom thrid, or leave it in the middle with the post a bit below it. My cheek weld didn't really change per se, but I could tilt my head forward/aft slightly to change the relationship in the two.

4) Front and rear both up. Everything lines up in the bottom 1/3 of the optic. Of course I didn't shoot it tonight, but from standing there aiming at a nail on my basement wall, I no more had to just slightly "nod" fore or aft with my head to get the sights to align when they were "up" when compared to my normal sight picture when my sights were folded