Monday, November 19, 2012

What I Learned in 100 Rounds - How to Zero an AR15

What I Learned in 100 Rounds - How to Zero an AR15

Fresh out of the box, you picked up your new AR15 and giggly as a schoolgirl blasted away several magazines worth of ammo on the 25-yard range making cans dance... well kind of. Unless you ordered a Houlding Precision custom HPF-15 AR and it came perfectly zero’ed, it was probably clear to you that your new AR needed to be zero’ed, but what is the best method and zeroing point?

We have all seen the person becoming more and more frustrated with each round sent downrange at a 100-yard target attempting to zero their new rifle or optics.  You hear their muffled cries as the bolt locks back from yet another empty magazine all while a pristinely clean target still exists down at the 100-yard line.  My tips will help you not be that guy.


I have been that guy at the range and the embarrassment, although years ago, is still a painful memory. I remember the point where a very old centurion shooter said “maybe you should start with zeroing a little closer”.  This concept of zeroing at a close range technique is actually the standard military method for zeroing most military rifles including the M-16/AR-15 rifles.  This method will save you boatloads of frustration and will get you perfectly zero’ed in around a dozen rounds. 


In this case, I will be zeroing my a newly attached Eotech sight on my Houlding Precision Custom HPF-15 AR15 and checking the zero on my Spikes Tactical ST15’s iron sights and assuring my co-witnessed Vortex red dot sight is on the mark as well.

USING THE 25M ZERO & WHY IT WORKS
The military has found that the ballistic trajectory a typical .223/5.56 Nato round hits the same point of aim at 25M and 300M with a military spec round. This means that zeroing your rifle at 25M will put you pretty close to dead on at the 250M-300M range with most .223/5.56 Nato ammo. The 5.56 Nato/.223 round ballistically delivers a relatively flat trajectory everything in between on center of mass man sized targets out to around 375 yards with minimal adjustment in combat situations.  


The trajectory of a standard .223/5.56 NATO round with the 25M zero will put the point of aim at around 4-5” high at 100M.  Using this zeroing method, the shooter can even deliver 400 and 500 yards shots with a simple holdover of 12" for 400 yard targets and about 36' for 500 yard targets.  It is an AR zeroing method which has stood the test of time and is practical even at short combat distances as well.

ASSURING SIMILAR ZEROING
The 25M zero allows me to have a bit more fun when I go out shooting versus spending all my time understanding where this rifle is shooting.  Zero all your ARs at 25 Meters with the same base ammo and you will truly enjoy life more with less frustration.

From a practical perspective I have found this zeroing method to be relevant in all but those rare situations where a ballistically calibrated scope reticle requires a 100 yard or 100 meter zero. For iron sighted ARs or ARs with red dots a 25M zero is the way every single AR I own is zero’ed with 55gr 3GunAmmo.com loads and affords me the option of putting reliable shots on target with any AR out of my safe. Yes, I am a huge advocate of assuring all your similar rifles all are zero’ed the same way otherwise it is far too confusing for my simple mind to remember whether this gun was zero’ed for 100, 150, 200, 300, or something else.


One of the other keys to ensuring a repeatable zero is to use the same ammo you plan on using for sport or defense. Your practice ammo should be the same or have the same ballistic trajectory as your high end ammo.  My preference has been to use .223 55gr and 62gr rounds from 3GunAmmo.com.  I have found 3GunAmmo.com extremely consistent, reliable, accurate and reloadable all for the just a bit more than inexpensive steel case ammo.

At the 0-100-yard ranges, I have found most .223/5.56 Nato ammo to prints about the same point of impact within an 1” or so regardless of bullet weight and ammo brand as long as the velocity is similar. Beyond 100 yards, the point of impact changes based on the velocity, bullet weight, and aerodynamics of the round.  


The iStrelok iPhone/Droid Ballistic app chart shown below is an example of 3gunammo.com 62 grain rounds shot from my Houlding Precision 18" barreled AR and should be very close to what you will see with most .223 rounds - Note this chart reflects yards.  As they say, your mileage may vary based on which round you select to zero your rifle, however the below chart gives you a general idea of the flight path of the bullet from your AR with a 25M zero.  The X-axis is in yards and the elevation x-Axis is in inches.  Attaching this chart to your stock or scope makes it easy to hit targets from 0-500 meters.

HOW TO ZERO YOUR AR
One of the all time best AR15 25M/300M zeroing targets I have found is the free (yes free) printable, downloadable and savable BobDBob.com 25M AR15 Zeroing targets here. I prefer these over a standard bulls-eye target because the AR15 Zeroing target has a grid that gives you the appropriate windage and elevation adjustments

I have created a target stand to hold my targets, however you can just staple these targets to a an existing stand at the range or fabricate your own target stand. Caldwell has a nice little Portable Target Stand for around $22, which is available from most sporting retailers.

Print out a half dozen of these targets and measure off 25 meters (82 feet) from the muzzle of your AR on the bench or from a board mounted target back to where you can position your muzzle at the 25M point.  Remember 25M does not equal 25 paces or 25 yards. Yes, measure it with a ruler to 82 feet or with a laser rangefinder. I recommend picking up a cheap 100 foot landscaping ruler for this chore as a couple feet either way will impact the precision of your zero from rifle to rifle.

If possible the target should be mounted as level as possible to the height of the AR.  If I use short ground mounted targets, I usually shoot from a prone position on the ground. After you have assured the target is 82 feet/25 meters from the muzzle of your AR, the next step is ensuring you have a solid rest to shoot from. Zeroing should be done from a benchrest or prone position with a bipod, sandbags, bean bags, or rice bags.  Most of the time I shoot from my pictured Atlas bipod however I do shoot form bags as well. Personally I have found bags of rice or beans to work just as well and are less expensive than sandbags, and of course if the situation arose they could be cooked and eaten. Usually I alternate bags of beans and rice in a heavy duty Ziplock freezer bag to elevate my handguard enough to comfortably put me on target and an extra bag under the stock to facilitate incremental adjustments.  


Get locked in behind the rifle and shoot a three shot group.  If you are not on the paper, you will need to move the target closer; generally the 10-15 yard line, however in most cases you should see a nice little cluster somewhere on the target.  The linked BobDBob.com target has the appropriate clicks up and down for Mil-Spec iron sights, I have found that Magpul sights are close, but do not match these clicks perfectly.  The target gives you a grid guide which enables you to make the appropriate number of left or right click adjustments to both the front and rear sights.  Making the required sight adjustments should deliver the next three shots on the center black silhouette.  After the second group, make any minor adjustments and shoot a final group assuring your shots are dead center. If no further adjustment is required, I usually shoot another three-five shot group to assure my 25M average group is dead center.

FINAL THOUGHTS
It had been a while since I checked the zeroing on my Spikes ST15 and this exercise
demonstrated that it is good to check this once in a while; the rifles was a couple clicks out of alignment. Once those adjustment were made on the ST15, I mounted the co-witnessed Vortex Sparc and used the iron sights as a reference point to zero the red dot.  This is one reason I like to have back up sight with a red dot equipped rifle; if you ever remove and reattach or knock something out of alignment, you can double check them against each other.  I then attached the included 2X multiplier on the Vortex and shot a three round group at 25M which was perfectly dead center. 


I repeated the same process with the Houlding Precision HPF-15, however the sights were perfectly zero’ed and all that was required was to assure my co-witnessed Eotech sight was also zero’ed at 25M. The only thing left to do is to verify that at 100M and 300M that you are not a click off on windage left or right.  I am fortunate that at our range, we have a 12” 300-meter steel gong which makes it really easy to validate a rifle is delivering a 300-meter zero. Three satisfying hits in a row with both AR15s on the 300M gong put a smile on my face and instilled the confidence that I could deliver hits on any 12” target within 0-300M.  If you followed the above steps your AR will be properly zero’ed and can easily deliver the same accurate hit out to 300M.


Obviously the name of this new series is "What I learned in 100 Rounds", but I only used about 20 rounds for each rifle to complete the zeroing; what did I do with the other 60 rounds? I had fun plinking away at golf balls and Coke cans at 25, 50 and 100 yards understanding the holdovers at each range... it is a lot more fun once your AR15 is perfectly zero'ed.
SOURCES
Houlding Precision
http://www.houldingprecisionfirearms.com/

Spikes Tactical
http://www.spikestactical.com/new/z/index.php

BobDBob
http://www.bobdbob.com/~deneb/doc/targets/m16a2-25m-zero.pdf


Eotech
http://www.eotech-inc.com/

Vortex Optics
http://www.vortexoptics.com/

No comments: