In many of the discussions I’ve had with both like-minded and comparably-experienced folks, including some in my inner-circle, the topic of LRM comes up with usually two platforms in mind; the AR in 5.56 and a Bolt gun, commonly in 308 (7.62×51). To a man, we recognize the distinct advantage of the rifleman, not only from the discipline being the hallmark of a warrior but also that we can reclaim that
Infantryman’s Half-Kilometer and with it provide an advantage over the OPFOR like none other. Paramount to that capability is understanding your zero and not only how to correctly perform it, but keep it in unpredictable conditions.
Obtaining the correct zero on your rifle is frequently the most misunderstood element of riflecraft, with the utility of a sling slightly behind. A zero is the correction of your point of aim (POA) to your point of impact (POI). This changes according to distance of shot, bullet weight and charge, and environmental conditions. Our article will deal with the basics surrounding the first and how it can be affected by the second. The first issue to resolve is the fundamentals of good marksmanship, second is the actual distance of zero, third is understanding the mechanics of the action and conditions of which you’ve zeroed your weapon. They each make a tremendous amount of difference in both being able to zero and shooting your rifle true. A misunderstanding of any of these potential issues will cause a frustrating day at the range or a missed shot when it counts. For example, I don’t often comment on other blogs but this question was sent in my direction for guidance:
The bedding of the stock meeting the rest caused the shift on the M14/M1A. The handguard caused the shift on the AR platforms. This is why we freefloat actions as much as possible by either glassbedding the Garand action or using any of the common [accurizing, more commonly known as freefloat] tubes for the AR. This is why DMRs and Snipers make sandsocks as an improvised rest. Mine never wanders far.
When you zero do it from the prone, supported from that sandsock just behind the sling swivel. It’ll have the least impact on your dope. Zero at 100m.
Let’s explain a bit and expound.
The fundamentals of proper marksmanship, Breathe, Relax, Aim, Squeeze- not tap/rack/bang, bang, bang till you hit something – are the cornerstone of what you should be working on each and every time you hit the square range. In fact, that should be all you’re doing until you have it mastered. Consistency is the key. Body alignment and sight picture are corrected through focusing on these fundamentals, because no matter what you’re doing as long as its the exact same everytime and gets those rounds on target, then it’s not wrong. But what I will say about this is that just like a golf swing, the proper technique needs to be taught by those that know what they’re doing, or you’ll never actually be able to diagnose those minor problems with the fundamentals that even well-seasoned shooters have.
Distance of Zero
This is the biggest point of contention when it comes to a solid zero- traditional thinking says that one needs to zero at a closer distance, usually 25m to account for the rise in bullet trajectory up close to match that of the drop further out, common knowledge being 375m when talking about the 5.56 AR-15. For iron sights and red dot optics, this is the preferred method along with the associated points of aim in the illustration above. But for an optic with a Bullet Drop Compensator (BDC) or Mil-Dots of any variety, different distance zeroes are usually required. For some of the more common reticles out there, such as the ACOG TA-01 and TA-31, the Burris AR and MTAC series BDCs and the excellent Primary Arms ACSS reticle ( which will be covered in a post of it’s own in the near-future), they each have a specific distance zero to function. Most of the time this is 100m.
Here’s another problem with BDCs, albeit a minor one. Along with being tailored to a distance, they’re usually also tailored to a specific ( or average thereof) loading. The shooter must know the bullet weight and speed in addition to just the caliber and barrel length and twist they’re shooting. 55gr M193 has a slightly different trajectory than 62gr M855, which has a different trajectory from 77gr OTM. The ACOG TA-31, for example, are tailored for 62gr M855 from the 14.5in M4 barrel. Each loading data is slightly different, with 308 having a fairly wide trajectory margin between those possible loadings due to a large variance in the bullet weights and types available, the most common usually being 147gr M80 Ball. For example, a 1/7 twist rate will be different from a 1/8 or 1/9 in 223 or 5.56. 1/10 is gonna be different from 1/11.25 or 1/12 in 308 or 7.62×51. Barrel length is yet another variable affecting velocity. And since it’s all based on averages, there’s no replacement for actually confirming that Data On Previous Engagement (DOPE), by actually putting rounds on target at 200, 300, and beyond, preferably training with someone who knows what they’re doing.
The excellent ACSS reticle from Primary Arms
Confused? Don’t be. Just go shoot and confirm the impact of rounds at those ranges. That said, I like BDC reticles for many reasons, mainly due to convenience and the speed at which I can train someone on their use. I just confirm the actual points of impact for each of the stadia lines with the round I’m running. Along with the very fast rangefinding method built into both the ACOG (
seen above) and the ACSS ( seen left) a rifleman can rapidly range his targets when completely exhausted and not always able to think.
Let’s pause for a little fieldcraft professional development- the first thing any Scout or Sniper does once the hide is emplaced is range off the Target Reference Points (TRPs)
A rough sector sketch range card from an urban hide. Above is a drawing of my sector. All numbers are in Meters.
The rear of the above range card, with basic necessary reporting information.
so that he knows the relative distance of everything within his Field Of View (FOV). These are a requirement for every fixed position. TRPs are simply big objects that you can’t miss, like a building, a door, the intersection of a road you’re watching or that huge century oak just to the left of it. The schoolhouse answer is to write it all down on a range card, which is a printed piece of paper that you’d carry on a small clipboard in a ziploc bag. In my experience paper turns to mush from the sweat you put out during a movement to the hide, and the actual range card even when laminated gets kinda convoluted after a couple days of little sleep and silent boredom. I have an easier method. Carry a few pieces of thick cardboard. Draw a rough picture of the lay of the land, exactly as you see it. Write in the distance in meters above each item. Do it all in permanent marker- they don’t run and they write on most surfaces damp or dry. It also writes big and easy to see, so that anyone can read my chicken scratch. What does this have to do with zeroing a rifle? If you know the engagement range of your target and the impact data of your weapon, you’re combat effective. The rangfinding reticle of a mil-dot or BDC-type reticle from above enables you to do just that rapidly and simply. Alright, PD over, let’s get back on track.
Mechanics of the Action and Zeroing Conditions
A drawing of a harmonic stabilizer on a bolt action. The perforated line represents the meeting of the stock and the barrel. The stabilizer is designed to minimize the impact of the stock upon the barrel.
As a round travels down the tube, the barrel itself flexes. Anything touching that barrel impedes this natural process. Further, those things touching the barrel have a slight to major impact on the POI versus the POA. For this reason the most accurate actions are free-floated and/or glass bedded to attain the best accuracy possible. This is very simple and a standard upgrade for any bolt action. For an AR-15, the closest you can get to a freefloat is one of the hundreds of handguard tubes on the market, and the longer the better for accuracy’s sake when shooting from improvised rests. Anything you place under the handguard will have little impact on the barrel, keeping your zero true. For the Garand action/M1A/M14, imperfections in the original stock or warping from moisture causes shifts in zero, which is the big reason the Ordinance Dept. got away from wood stocks (
and you should too). Glass bedding provides a perfect smooth surface along with a more precise fitment of the stock to the action. It’s also important to note, like I did in the original excerpt above, that the Garand action is least affected by the use of a rest if the forward rest is placed just behind the sling swivel. There’s a little more material behind the swivel due to the stock taper so it has less impact on the barrel and shifting the gas piston beneath it.
On that note, let’s address the mechanics of our zero. In order to have a true zero, we have to eliminate as many impacts on the action as possible. Zeroing from a sled or bench rest is nice for testing the mechanical accuracy of an action, but in practice they’re good for little else in terms of practicality. You do not fire a weapon the same way from a bench rest the same as you would naturally from the prone.
Meet Fifi the Sandsock. Fifi has been around the block.
Your head and body position is different, which means your sight picture, even from optics, is also different. Along with that if you’ve laid the weapon in the rest improperly (
such as resting any part of the barrel on the rest itself) your zero is now ineffective. This is the exact same as resting the barrel on a surface you’re firing from, such as a window ledge or log. A proper zero and confirmation of DOPE is conducted from the prone.
The best item a rifleman can carry to the range and on a patrol for accuracy is a sandsock. Take two old socks, fill one with about a pound and a half of sand, tie it off and put it in the second sock. Now you have a nice little sandbag that flexes to any surface you may find yourself shooting from and conforms to the weapon. It can also make a nice little neck pillow for those little ad-hoc naps in the field. They cost nothing to produce and make you more effective.
Being a competent rifleman starts with obtaining the best zero possible. This is accomplished through solid practice of the fundamentals, understanding the mechanics of your action, and zeroing the same way you’ll be shooting in the real world. Knowledge of the trajectory of your rounds and how your chosen method of aim, be it iron sights all the way to a 4-14x44mm scope, work together is critical to repeatable firing solutions. And above all else, gaining that knowledge though solid, competent training is a must. A seasoned team of solid riflemen effectively employing the basics of good marksmanship and fieldcraft can dominate a battlespace as history has proven over and over. That rifle sitting in the safe is ineffective all alone- seek out good training and push yourself beyond your comfort zone!