Okay, I've noticed a lot of the ARs have optics mounted on top and also have back-up iron sights. I was wondering, what is the point of having both of these? Can't you only use the BUIS if you remove the optics?

The concept has been around for a while. The military is going toward optics now; Aimpoints, ACOGs, and EOTECHs.Optics are generally easier to use and faster on target, but more fragile and subject to failure. BUIS are in case of thatunfortunate situation. Most optics for such rifes are easily removed by hand tightened screw mounts or cam lever clamps.

If you are using optics with no magnification such as Aimpoints, Eotechs, C-more red dots, etc, you can get your back up iron sights to "co-witness."
This means you can still index your irons through the glass of the red dot sight.  All of these optics mentioned are battery powered.  What this means is your battery can go out, internal electronics can get damaged or short out,  or just plain stop working from banging around or constant recoil.  When this happens you need iron sights to continue.  This ofcourse is an issue for our men and women in battle as well as our law enforcement.  For most people like us, we have the luxury of taking a break to insert new batteries, order new optics when they fail, or simply pack up from the range and go home.  If you ask most military personnel they will tell you the shit fails when you need it most, at that point your back up irons are a life saver.  The other malfunction you may encounter with optics is if your glass breaks.

Aimpoints are the most reliable, Eotech's reticle is useful, however no where near as reliable as an Aimpoint.  Also Aimpoints generally have better battery life than Eotechs.  Depending on the model, some aimpoints  can go 50,000 hours on mid level dot intensity.  I personally have never had an Aimpoint go out on me.  I am also not in the desert day in and day out, banging my rifle around, clearing houses, diving for cover, and much less returning fire constantly.  But from a personal preference Aimpoints are all I run.

Forgot to mention, if you are using magnified optics on a gun say an AR set up as a SPR or counter sniper weapon, you would want a quick detach scope mount such as a Larue SPR mount.  If your optics fail, flip two levers, and the optics are off enabling you to go to irons.  Larue mounts are awesome!  You could zero your weapon, pull the optics off, put it back on, and it will still keep zero!  I know of some operators hating on ARMS QD mounts stating they dont keep zero, even when on the rifle.

So, really, you can only useful if you unmount your scope?

There are scope mounts that are elevated and allow you to use the iron sights by peering under the optics.  Like these.  While I've only seen them on sporting rifles or handguns so far, there's no conceptual reason a person couldn't mount them on an AR. 

So, really, you can only useful if you unmount your scope?

As Tom mentioned the scope rings that allow you to peer under the scope are excellent for sporting rifles or handguns.  This works well because the iron sights sit right on top of the bore axis.  On an AR platform, you will most likely be using flip ups in the front and rear as back up irons or using a flip up rear sight along with the A2 front site base which is fixed and generally high in relation to the bore axis.  Because of this, the field of view under the rings may not allow you to see your sights.

So as an answer to your question, if you are looking to use your irons as back ups to say the scope mounted to your 10/22 then no, you would not have to dismount your scope.  However, if you wanted to use your back up sights on an AR then yes, you will most likely have remove your magnified optic.  Finally, if you are using an Aimpoint or Eotech where the irons co-witness with the glass of the optic then you could carry on shooting without removing even if there is a malfunction or if your batteries run dry.

Hope this helps!

I run magnified optics (Leupold) or Aimpoint T-1 on my AR, situation depending. I also have backup iron sights (BUIS).


When running the scope, the BIUS are useless. I have quick release levered scope mounts, so I can get them off quick and swap on the Aimpoint or go to BUIS only. The red dot is on a Larue quick release. Someone mentioned co-witness
on a rifle, this is great if you find yourself with a non-functional red dot. This allows you to flip up the BUIS and aquire the target through the red dot optics even if they are not functional. Aimpoint T-1s have a battery life of 50,000 hours. I don't even turn mine off.   I practice with all possible combos on my AR to ensure I know what to expect from the rifle. (Scope, Red dot, BIUS only, BIUS with Aimpoint mounted, but dot on/off -cowitnessed.)


I personally love the aimpoint T-1. It is tough as hell, lightweight, and allows for very quick target aquisition and follow up shots. Pricey, but worth it IMHO. Eotechs are cool, heavier, eat batteries quicker, and break easier. Each has its purpose and its fans. Find a gunshop that will let you mount both up on your AR (or plaform of choice) before you buy. This way you can decide before you spend several hundred dollars.


My $.02
 

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BUIS are just exactly that... for back up. Most people who are running reflexive red dot sights are more then likely electronic. Anything electronic/delicate (to an extent) has the potential to fail. In the instance that your optic fails, you have your back up iron sights so you're not quite yet out of the fight. EOTechs, Aimpoints and even the Trijicon's all have the capability of being able to co-witnessed, where you can align all 3 together on the same plane. So if you're optic fails, you can flip the front, rear, or both up and you're back in action.

As far as magnified optics are concerned, you would require a quick detach mount like mentioned above before you could actually flip up your irons.