Ask Foghorn: Use Both Iron Sights and a Red Dot?

Jim writes:

I have not been into guns since I left Viet Nam. When I came home I did not want to see guns much less shoot them. Now I am older and maybe wiser. I am trying to set up a DPMS Ar 15 and I would like the ability to use both iron sights and red dot. I have a SightMark red dot on the rifle now and want to include iron sights because I am so use to them from the service. What is the best and most secure way to attach both sights??

First, thank you for your service. Second, I think you’re talking about co-witnessing your sights.

There are a number of reasons for having both iron sights and an optic of some sort on your rifle. The first reason is keeping everything aligned. For someone like me who swaps their optics around their rifles like a teenager getting dressed for her first date, having a fixed reference point to quickly re-zero the optics is essential. Thanks to the iron sights that are always on the gun, I can co-witness the optics and get (more or less) the same zero every time.

The second reason is as a backup. Powered optics need batteries which eventually wear out. And because they’re electronic devices, they have a tendency to malfunction. So when the red dot kicks the bucket the iron sights are right there and already zeroed. And they’ll never run out of batteries.

With the AR-15 system, setting this up is pretty easy. The standard M4-profile upper receiver has a fixed front sight post, that triangle-looking thing on the front there. So thanks to that fixed front sight, you’ll only need a rear sight.

If you don’t have that fixed front sight then you’re going to need to get one of some sort, and that will differ depending on how your rifle is designed. Having a railed gas block will make things easier, as will having a full length top rail. You can just pop a front sight onto either of those and it will work just fine. Worst case scenario, you can always find a bolt-on or screw-on rail section and fix that to the rifle.

If you have an A4 style upper with the rail on top instead of the carry handle, then you’re already set to get the co-witness working. Pick an optic of your choice and a rear sight of your choice, and slap them on the rail (with the rear sight closer to your face) as seen above. If you have an A1 or A2 style upper then life will be a little more difficult, as you will need to figure out how to get the optic on the gun as there is no standard rail.

Once you’re done, follow these instructions to get everything lined up.

[Email your firearms-related questions to “Ask Foghorn” via guntruth@me.com. Click here to browse previous posts]

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About Nick Leghorn

Nick Leghorn is a gun nerd living and working in San Antonio, Texas. In his free time, he's a competition shooter (USPSA, 3-gun and NRA High Power), aspiring pilot, and enjoys mixing statistics and science with firearms. Now on sale: Getting Started with Firearms by yours truly!

9 Responses to Ask Foghorn: Use Both Iron Sights and a Red Dot?

  1. avatarMark says:

    I like the concept of using Dueck Defense Rapid Transition Sights for close with a scope for longer ranges.

  2. avatarSanchanim says:

    So basically if I have a “standard” front site I can just get a red dot rear, and away I go!
    I guess you could have an iron site on the back too, but I don’t think I would need it.

  3. avatarWade says:

    With my EOTech, I put just a folding front sight on, no rear. That way, if the battery goes dead I can just flip up the front sight, and center it in the middle of the EOTech window. It works just fine for 2 or 3 MOA.

  4. avatarSanchanim says:

    I saw a red/green dot sight the other day for around $199 and it had a quick release as well. I forget the name of it darn it.

  5. avatarT says:

    Get a good fold-down rear sight to go with those red-dots. If for some ungodly reason your red-dot comes off the weapon, at least you still have a full set of irons.

    If you lose your BUIS, well then,

    From the Hip!

  6. avatarfitz19d says:

    Should add to this article offset sights. One of my AR’s now has a 4x with an offset fastfire2. The same could be applied to optic and offset iron sights. Personally I hate the obsession most have with cowitness. If I needed a iron sight option on top of my eotech on other AR, I’d offset the irons too, probably some flip ups on small DD 45 offsets.

  7. avatarTrey says:

    Hello there, on the “co-witness” topic can you give me a few suggestions on a red dot or holographic optic that would work with or should i say allign with my magpul gen 2 sights, I know about the $600 and up set ups but some descent optics in the $100 to $250 range? My rifle is a flattop M4 with a Spector length rail and low pro gas block…… Thanks

  8. avatarNate says:

    @Trey – in most cases, you get what you pay for. Or put it this way, if there were “decent optics in the $100 to $250 range” that were as good as the $600 setups, then that’s what everyone would buy and the $600+ options simply wouldn’t exist. There’s a reason that they cost more.

    I have an EOTech matched with a Primary Arms 3x (extended eye relief) magnifier and a flip-up mount. The whole setup cost $621 (shipping included). I’ve tinkered with the Burris fastfires and a number of other, less expensive, setups. None of them compared to the EOTech. Admittedly, “as good” and “good enough” are not the same thing. A fastfire may be “good enough”. But I can assure you that they aren’t as good as the more expensive setups.

  9. avatareric says:

    Dont have rifle yet. Thinking of running vortex strikeforce with magpul pop ups. This work?

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