Range Day, Part 2: Zeroing an AR-15

My second task at the range yesterday was to zero the sights on an AR-15.  I've had this one for awhile, but I recently installed a new front handguard, which could potentially change the point of impact, so I thought it prudent to confirm the zero before putting it back on the rack.

This AR-15 is a Colt LE6920, a standard run-of-the mill AR-15 in M4 configuration.  It has a standard front sight but no rear sight, so I have it mounted with a Troy folding rear sight as well as an EOTech 512 Holosight and folding EOTech 3x magnifier optic.  I also have a vertical front grip and FourSevens tactical light mounted on this rifle, along with a Condor 2-point tactical sling.  It's a very practical setup that has worked well for me, but I never did like the bulky MILSPEC quad-rail front handguard I'd installed, and decided that the Tekko M-Lok handguard would be a better choice.

Colt LE6920, a standard AR-15 with some accessories

"Zeroing" a rifle simply means adjusting the sights so that the point of impact/POI (where the bullets hit) is the same as the point of aim/POA (where you want the bullets to hit).  Conceptually, the process is very simple:  first, you fire the rifle to get a good, tight group of shots on the target.  Once you have a good, tight shot group, you measure the distance from the shot group on the target (POI) to where you wanted them to go (POA). Then you iteratively adjust the sights and fire additional shot groups until POI and POA are the same. In practice, many people have trouble with this process, usually because they try to adjust their sights before they have a good group, and end up chasing their shots all over the target.

I set up Appleseed grid targets at 25 meters. These are a very practical and precise zeroing target. You can learn how to use them (and a lot more about precision marksmanship) by going to an Appleseed Marksmanship Clinic.

Why 25 meters?  Usually we shoot rifles at longer distances than this.  The reason is a) It is much easier to zero at 25m than it is to walk back and forth to targets much farther away.  b) The math ensures that your zero at 25m will give you the data you need to adjust your sights for any other distance. c) Due to the ballistics of the bullet (which is still rising at 25m, then begins to drop when it's farther downrange) your zero at 25m ("near zero") will be same as it is at about 250m ("far zero"). You will have what is known as a "battle-sight zero", meaning if you simply aim for center mass, you will reliably hit somewhere on a service-rifle size target out to several hundred meters.  Every rifle/ammunition combination is different, but there are rules of thumb like this that apply - you just have to know your own rifle and ammunition.

To zero this rifle, I fired five round groups from the bench using PMC 5.56 M193 MILSPEC ammunition.  I've had this ammo since the late 1980s or early 1990s. My dad and I used to buy it by the case when we were regularly competing in high power rifle matches.  I don't shoot AR-15s as much anymore, so I am just slowly using it up in range sessions like this, as well as occasional plinking.

I started off by firing over the iron sights:

AR15 w/ iron sights at 25m.

I was very happy to see that the irons were right on target, especially because my eyes are not what they used to be, and I cannot bring a carbine-length front sight post into clear, crisp focus anymore.  The group above is not really quite what you'd like to see to call the sights "zeroed", but for me this was as well as I can hope to do on iron sights with this rifle, so I left them alone and proceeded on to the EOTech Holosight.

The EOTech 512 Holosight is an engineering marvel.  It projects a reticle onto a "heads-up" display, similar to the heads-up displays used in fighter jets.  This enables you to quickly get on target without worrying about exact sight alignment, maintaining better situational awareness by keeping both eyes open. You see this sight all the time in TV shows, movies, and news items about military operations, as it is standard issue for many units and is very popular with civilians and police as well.  Combined with the flip-away 3x magnifying optic, you are well equipped for encounters from close-quarters out to medium ranges (several hundred yards).  Provided the sight is properly zeroed, that is.

I fired five rounds through the Holosight, and was very pleased with my group:

First 5-round group through the EOTech Holosight.

I was actually measuring the slight adjustment to the left and down that would bring this group onto the black square next to it, when a nagging thought occurred to me.  Hadn't I actually meant to aim at the center square on the right-hand target?  I thought about this for a few minutes and was pretty sure I had, so I fired five more rounds, aiming at the center square on the right-hand target.

Second five-round group, same point of aim.

Sure enough, I had aimed at the right hand target, center square, and hit the left-hand target, upper right square.  *THIS* is why you have to zero your rifle sights!  I fired beautiful groups, but if I had not confirmed my zero, they'd be going off who knows where - certainly not on the target.  I took my measurements off the target grid and made the adjustments to the Holosight, and fired again.

Third 5-round group through the Holosight, after adjustment.

This was much better!  Elevation was dead on, but for some reason the horizontal adjustment wasn't right.  Perhaps I miscounted the clicks or something.  In any case, I measured and made the adjustment to move the group to the right, and fired five more shots.

This time the group hit the center square I was aiming at.  It seemed a little to the right, but also wasn't quite as tight a group.  I wasn't sure whether this was shooter error or another required adjustment, so I fired another 5-round group at the lower left square without making any changes.  Since the POI was almost identical to the group on the center square, I made a slight adjustment left and fired one more 5-round group into the lower right square:

Final target with Holosight zeroed (lower right square).

I was very satisfied with this result.  With the rifle properly zeroed, I transitioned into some fun shooting at other targets, until it was time to go home.   The take-home lesson here is to *always* reconfirm your zero after you change anything on your rifle.  It doesn't matter how good a shot you are if your sights are not on target!

Mood:  Happy
Music: Cuckoo Clock (again!)