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.

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