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Old 06-19-2012, 09:20 PM   #11
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Normally you chose a mount/riser that gives you the right height for cowitness. A taller mount is required for bottom 1/3 than absolute. Look at Purehavoc's diagram and decide which you want. I like bottom 1/3 myself but many like absolute.
thanks, but this is still where i'm at a loss.....how do you know what mount/riser is right for which type of co-witness?
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Old 06-19-2012, 09:27 PM   #12
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Some of it is good old-fashioned research and math. The nicer scopes (not NcStar or Millet) will have on their website every possible measurement for you to see. If you measure your iron sights (or use website measurements if using BUIS like Magpul, etc.) you can know what #'s to look for.

Also, some Red dots have mounts specifically designed to provide cowitness through standard AR-15 iron sights. I am thinking the Burris Fastfire with its AR-F3 mount. I'm sure there are others in this category.

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Old 06-19-2012, 09:33 PM   #13
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I have a lower 1/3 co-witness and the center of my optic is 1.75 inches above the top of the receiver.

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Old 06-19-2012, 09:36 PM   #14
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You might check with Millet and also read through user reviews of that model at Cabelas, Brownells, Midway, etc., someone may say. You could get a steady handed friend hold it to the correct height and measure. Tall mounts are probably very close but that's just a guess.

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Old 06-19-2012, 09:38 PM   #15
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My setup which is Eotech XPS2-0 with Magpul front+rear. It has obsolute cowitness.

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Old 06-19-2012, 09:42 PM   #16
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I have a lower 1/3 co-witness and the center of my optic is 1.75 inches above the top of the receiver.
hawkguy, Looks like you found a steady handed friend.

You may need very tall risers for 1.75 in. I'm not near my ARs but guess my mount is about that tall.
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Old 06-19-2012, 09:42 PM   #17
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The biggest problem you will have is trying to find accurate dimensions before you buy. From what others have said on other forums the center of the optic needs to be 1.5 inches above the receiver for absolute co-witness. 1.75 for lower 1/3. With a 1 inch OD tube the inside of the bottom ring should be 1 1/4 inches above the top of the receiver for lower 1/3. if it 1 inch ID subtract the the wall thickness of the tube from the bottom of the ring. but again getting ACCURATE dimensions from web sights won't be easy.

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Old 06-23-2012, 03:18 AM   #18
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Default thanks EW1066

took a chance on the ncstar mount you suggested (it was only $30, so...)

this mount, with my existing red dot, seem to co-witness well. just from looking through, it seems to be an absolute co-witness, as when i have a proper cheek weld, my dot does seem to sit right on top of my front post.

i know only time will tell, but so far it seems like a solid mount that will work out great. i'm pretty excited cause i actually bought this millet red dot for $25 used (normally $80+), putting my total investment at about $50-60. i used this millet red dot on my mini and for the $, it seems to be a very good optic.

i realize this is a pretty "cheap" set up, but it will be nice to fool around with a red dot on my new AR, until i can save up for something better.

here's a pic

m-p-sport-red-dot.jpg  
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Old 06-23-2012, 05:14 AM   #19
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You are welcome. I like to help in any way I can.

Don't forget a range report. Would like to hear how it works out in actual use.

EDUB

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Old 06-23-2012, 04:04 PM   #20
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I prefer absolute co-witness. Can't really explain why, it just feels "right" to me.

But a person really should try several options, and use the one that "feels right."

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