Co-witness question

Discussion in 'AR-15 Discussion' started by purehavoc, Dec 19, 2011.

  1. purehavoc

    purehavoc New Member

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    My Carbine should be here any day and I needed a rear sight , so I bought a Magpul MBUS rear , My question is will I be able to Co-witness thru a Primary Arms microdot with this setup or is it to small ? It says lower 1/3 on the ad but I want to know from someone using that setup that it works.
    If you believed everything you read the world would be a 110% happy place
     
  2. JonM

    JonM Moderator

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    well if your referring to co-witness when looking through the sights and the sights and dot are on the poa at the same time while looking through both, then No. your dot will be above the target when using irons and your irons under the target when using the dot.

    i prefer absolute co-witness when both are poa at the same time. magpul mbus height is 1.5" above rail. heights are typically measured to the center of the optic. so you would need a mount that puts the center level with the sights

    got a link to the sight your looking at??
     
    Last edited: Dec 19, 2011

  3. purehavoc

    purehavoc New Member

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    https://www.primaryarms.com/Primary_Arms_Micro_Dot_With_Kill_Flash_PA_Ris_p/md08pariserbundle.htm


     
  4. purehavoc

    purehavoc New Member

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    I guess my question is is it going to fall in the lower 1/3 with irons on the front and theh MBUS on the back ? absolute would be great but if it works Im not going to be that picky for the price .
     
  5. JonM

    JonM Moderator

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    from looking at their page it doesnt come with a mount. the drop down has a absolute co-witness addon for 40$ i could be reading it wrong. you might want to call them and ask

    ive got the vortex sparc and strikefire. the sparc comes with mounts for 1/3 and absolute. the strikefire comes with an absolute or no mount.

    military arms channel on youtube has a sparc review and order code for 20$ off from 3 rivers precision. one of the vendors for the forum here might be able to beat both prices
     
    Last edited: Dec 19, 2011
  6. AgentTikki

    AgentTikki New Member

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    The pa model comes with alow mount, unsuitable for use on a conventional ar flatop.

    You much opt for an additional mount. Thbe qd mount by pa is for a lower 1/3 co witness.
     
  7. purehavoc

    purehavoc New Member

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    I did get the PA QD mount for it , I just wonder if the extra $40 is worth it for the absolute ? What ya think I can call and get my order changed before it ships this morning
     
  8. AgentTikki

    AgentTikki New Member

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    I'm pretty sure you can.

    I prefer lower 1/3 over Absolute.

    Hey that sounds like a drink.......
     
  9. AgentTikki

    AgentTikki New Member

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    The difference is pretty small, my belief is that the best system would be more closely suited to you physical attributes.

    How tall and what size hat do you wear. Is you head the size of a grapfruit or watermelon ? o_O

    Lol I kid.

    An absolute is more suited to smaller heads. Lower 1/3 for bigger heads imo. A consistent check weld must be practiced and developed first for you to even form an opinion. Don't stress too much about it.
     
  10. Quentin

    Quentin New Member

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    I haven't worked with those RDS/mounts you ordered but with my TRS-25 and a tall mount I get a bottom 1/3 cowitness with my MBUS, which I like for zeroing as the dot is lollipoped on the A2 front sight when I look through the aperture. If I look over the rear sight the dot is floating above the front sight, maybe at a top 1/3. If I flip down the MBUS the dot is in the center of the glass. Is this how you want to set up your RDS purehavoc?

    Of course as AgentTikki pointed out I do have to change my cheek weld to move the dot around. Normally of course the MBUS is down because the dot is much dimmer when you look through the aperture.
     
  11. purehavoc

    purehavoc New Member

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    I talked to Scott @ Primary and he said the lower 1/3 is more prefered as absolute is very understood alot , he stated it as your front pin is absolutely covered with the dot which does you no good unless you shut the dot off as it makes it very difficult to get the front pin placement exact at long distances due to the larger dot being in the way and blocking the view .
    I got what I was looking for I just wanted to assure myself I ordered what I wanted .
     
  12. purehavoc

    purehavoc New Member

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    I stole this from another site and found it quite helpful

    [​IMG]
     
  13. purehavoc

    purehavoc New Member

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    Seems as though 1/3 gives you more sight picture , just seems more useful for my own use , Im sure others have their own personal preferences
     
  14. JonM

    JonM Moderator

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    I prefer the absolute. But im new to the dot sight thing. My irons on my dot sight rifles are flip up which makes it super easy to confirm the dot sight hasnt shifted. Absolute with flip ups makes it easy to zero the dot sight without having to shoot the rifle then flip the sights down.

    Just my take on it
     
  15. AgentTikki

    AgentTikki New Member

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    eh? huh? what?

    I dunno what he's referring too. Putting the dot on the tip of your front sight post will get you on paper, assuming your irons are sighted in correctly. But you should sight it seperately. I always find that you need to make a few adjustments. Tho both of my RDS didn't take more than a couple clicks of adjustment, I did have to make them.

    Whether you run absolute or lower 1/3, the front sight will invariably be mostly out of the picture. The beauty of the RDS is that you don't have to have the same exactly check weld, like you do if you were using irons. With Irons you want your eye in the exact same place so that its easier for you to line up your sights. With a RDS you want a consistent check weld so that the dot in the same place every time you shoulder your weapon. You don't even look at the RDS. You focus on your target throught it, and let the system put a dot up for you. In the diagrams you posted, both sighting sytems will look about the same as the center diagram when you are using your red dot. The difference is that absolute will take up a little more of the window. I mean the difference we are talking about is like 3/8s of an inch. Its really not too much of a big deal. I have 2 Aimpoints both on KAC mounts. I chose the KACs because the heights are adjustable to 3 different levels, (it comes with 2 spacers) I've played around with the heights, and found lower 1/3 to be more comfortable for me on my carbine, and on my pistol I use no spacers because of the rise on my rail given by my VLTOR rail, (which makes it more like a lower 1/4 cowitness! :p)
     
  16. Quentin

    Quentin New Member

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    purehavoc, the images in the center and right of the picture you pasted in is pretty much what I was describing. Center - looking over the irons - and right - looking through the MBUS aperture. Normally my sight picture is like the center except that I have the MBUS flipped down to increase field of vision/reduce clutter.


     
  17. AgentTikki

    AgentTikki New Member

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    I see that you are quoting a very respectible source, bravo :D