Why is it that most of the M4s I've seen in use by US SOFs have their Aimpoints mounted in a high mount (ARMS, Aimpoint, LaRue, etc) that doesn't co-witness with the iron sights?

Is this simply because the Aimpoint has to be that high to clear the AN-PEQ2 IR unit that most troops mount at the 12 o'clock position on their KAC RAS forends, or are there some tactical advantages I'm not thinking of?

Will  

new-arguy,

Really, the Aimpoints in a high mount will co-witness the irons?   My Aimpoint is mounted directly to my flattop in the low (no spacer) Aimpoint mount and it co-witnesses perfectly.  It just looks to me like those high mounts are too high...I guess you just have to adjust the elevation setting quite a bit with a high mount?

Will

I bought the Aimpoint with the mount from SWFA two years ago and was told that the mount (which appears to be unmarked) is also made by Aimpoint and is (was?) "US Military issue" at the time.  It attaches to the flattop via a large extended knurled thumbscrew that has a mechanism in it to prevent overtightening.  I had read here somewhere (can't find the thread now) that this mount is a older one and is still seen on some US weapons.  It appears from the side to be very low, but the dot cowitnesses right in the middle of the Aimpoint window.  

It works well for me--maybe it's my target rifle training but I just can't imagine using a higher cheek weld or adopting a more heads up shooting style...

Will

Thanks for the info new-arguy.  I guess I didn't realize that the higher mounts could be made to co-witness--I guess the Aimpoints have more flexibility in their elevation than I thought.

Will

If I may, you two do not see eye to eye. Ar guy is telling you that you can see the irons thru the tube, just fine, when mounted with thr 1/2" spacer. The sights, on  your rifle, Will, co-witness with out the spacer. Elevation change to'correct' alignment of the sights/Aimpoint when using the spacer could not be what he means. You would not 'adjust ele.' to obtain a co-witness, you would mount [lower] to obtain co-witness.  Your rifle co-witnesses as it is and if you use the spacer[most do], You can still use the irons, sight pic. lower than central thru the 'scope'. The spacer, you may find, might pick up your pace, if not target shooting.

Alan, thanks for your input.

Apparently I'm not defining the word "cowitness" correctly.  By cowitness I meant that the red dot on the Aimpoint would be perfectly positioned in a straight line between the rear sights and front post.

Apparently cowitness means "you can still see the irons through the optic", but they don't line up?

So my bad on the definition.  I guess I'm just dense, but it seems to me that if my Aimpoint was mounted in such a way that it was "floating" in space without close reference to the irons that it would throw my aim WAY off.  

Maybe I'm missing something else?  Thanks.

Will

If you center the dot in the tube, the irons should be in the bottom third portion of the optic.