[i]This is my reply to the same question from this thread in the [b]Optics[/b] forum.
[url]http://www.ar15.com/forums/topic.html?b=3&f=118&t=157407[/url][/i]
Do I need a mount that clears the field of vision through the optic? In plain english when I look through the damn thing do I want to be able to see the front sight post or not? Is seeing the front sight post through the optic what they refer to as co witnessing?
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First, remember that you use your irons OR your optic, NOT BOTH AT THE SAME TIME. To do so would defeat the simplicity of using an Aimpoint-type of sight.
Having your Aimpoint and iron sights [b]co-witnessed[/b], allows you to use your iron sights THROUGH your INOPERATIVE optic.
It would be great to have a clear field of view for your optic sight, nothing but "glass".
But whether you can do this depends on how you answer the following question: [b]"how fast do I need to access my iron sights in the event my optic sight fails"[/b]?
If you have a need to [i]instantly[/i] aim your weapon in the event your optic sight fails, then having your optic and iron sights co-witnessed is essential.
The trade-off for this capability is having your front sight in your optic field of view when you're using your optic sight. You will be looking over your rear sight aperture so at least that won't be in the way.
[img]http://www.imagestation.com/picture/sraid59/p2c737bfd262fd05a083e0f206f757178/fc5d0546.jpg[/img]
[i]NOTE: It was difficult for me to take this picture, and it doesn't depict what I want it to as well as I'd wanted it to. What I didn't do is focus the camera on the dot, which would've blurred the front sight.[/i]
THE FRONT SIGHT WILL NOT BE THIS CLEAR in actual use. As you focus on the TARGET, the front sight will "ghost" out to a large degree.
That's the tradeoff that you'll deal with, and not a bad tradeoff at all for the instant sighting capability.
Notice again that the rear sight aperture is out of the way.
This is the reason for using "spacers", to raise the height of the optic sight. We try and raise the sight high enough so that we can minimize the obstruction of the front sight assembly in the optic's field of view when we are using the optic as our primary aiming system.
We want to get the front sight assembly as low in the optic's field of view as we can, while still having it visible enough to get a good sight picture, if we have to go to irons.
Also, what would be the next step if something happened to the optic and it no longer funcioned how do I use the iron sights?
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Okay, the optic FAILS and the optic aiming point DISAPPEARS. You simply lower your cheekweld SLIGHTLY to look through the rear sight aperture and line up your irons THROUGH the inoperative optic sight, as if the optic sight ISN'T THERE.
[img]http://www.imagestation.com/picture/sraid59/pb43e619a439df4195f30f842c37fbfcc/fc5d0549.jpg[/img]
Chris