The Army 25-meter zero target. The dotted line is for when the aiming point is the bottom edge of the silhouette.
The Army 25-meter zero target. The dotted line is for when the aiming point is the bottom edge of the silhouette.
No matter how good your lawyer is, you aren’t getting out of obeying this basic law of nature: gravity works. A bullet hurled out into the air will, at the end of its journey, called the trajectory, fall to the ground. How long it takes for it to reach the ground depends on how fast it is going, the angle it leaves at, how well it shrugs off the drag air puts on it and, one factor that people overlook, how far down the ground is. You cannot throw or fire a bullet fast enough to avoid the ground. You can, if you accelerate it sufficiently, miss the ground entirely. This is called reaching escape velocity. If you are trying to reach escape velocity from Earth, that happens to be 25,000 miles per hour. Your rifle isn’t going to do that, as it equals 36,745 feet per second.
Hurled into a vacuum at an angle, a bullet would follow a circular arc from the point of origin to the ground. However, the effects of air will enter into the problem, and the result is the curved path the bullet takes, one called a parabola. At long range, the curve of the back half of the trajectory has markedly more curve than the front half. That is a parabola.
One of the design characteristics of the AR is that the barrel is directly in line with the buffer tube, which is also the part that bears on your shoulder. This creates a poor lever for the forces of recoil to act on, resulting in the straight-line recoil you experience. However, your eyes are not in your shoulder, and in order for you to aim, the sights (iron or optical) have to be up where your eyes are.
The design of this ends up with the sights of the AR-15 2.6 inches above the center of the bore. The end result is that you have to arrange the sights so that your line of sight, which is a straight line, and the parabola of the trajectory intersect at some point. This is referred to as “zeroing” your rifle. Additionally, you have to know what that point is or points are. Now, if you are shooting at a target, and you don’t shoot at any other distance, you can adjust your sights so that the point of aim (POA) and point of impact (POI) are one and the same at that one distance. Problem solved. If you shoot at different distances, say as a varmint hunter, or you are using an AR for defense, you have to know more than just that one distance.
And in a clever move, the Army had the sight correction rotations placed on the target, in the location they would be needed. (I probably shouldn’t be snarky, it is a good thing to have done.)
The arrangement also means that at close range, regardless of your zero (and we’ll cover that in excruciating detail in a bit) your point of impact will be below your point of aim. This is something that has to be learned and practiced if you are going to use the AR for defense. If you do not remember, or practice, a close-distance shot will have the bullet striking an inch or two below where you were aiming.
So, the line of sight is straight. The bullet arcs up, reaches its highest point, arcs down, and then finally falls to the ground. You have two choices; you can have the trajectory cross the line of sight once, or cross it twice. Well, you can have it not cross at all, but that isn’t much use, as you will always have your iron sights or red-dot scope and the aiming point, above where the bullet will strike. And the farther away the target, the greater the difference. Fat load of good that does you.
To do all this, regardless of what distance we wish to shoot at, we begin our work at twenty-five yards. Why twenty-five? In part, because we are lazy and don’t have time to waste. Yes, we could do our sight-in and zero at 100 yards, but we’d spend more time just walking down there and back than actually shooting and adjusting. At twenty-five yards you are far enough to get good info, but close enough to see the bullet holes without having to walk to the target. (Not that that keeps us from doing the walking any way. Sometimes you’ve just got to go down and look.) Plus it actually saves ammo. I’ve lost count of the times I’d be at the gun club and see a club member trying to sight-in his rifle at 100 yards. He couldn’t see, through his 3-9X scope on his .30-06, that his shots were missing the target. He’d have to walk down, guess, adjust and shoot more. If he had just started at 25, he would have seen he was off to the right, and gotten close enough to be on paper at 100.
Here’s the part that is difficult to grasp for some shooters: the POI at twenty-five yards is not always your POA. That is, at twenty-five yards, in some zero methods, the bullets will still strike below the point of aim. In this particular instance, useful, and not a contradiction of my snarky comment above.
The A1 sight still has a lot going for it.
Before we get into the details zeroing, we have to get square on what sights are, and what we do with them. Your AR has one of four types of sights. You have two iron sights, the A1 and the A2. And you have two optical sights, the red-dot and the magnifying. Yes, some optical sights can be both red-dots and magnifying, but we’ll deal with that when we get there.
The A1 sight has only windage adjustments on the rear. The adjustments are made by pressing in the plunger you can see in one of the openings in the flat wheel on the right side of the carry handle. With the plunger pressed down, you can turn the wheel to make windage corrections. The sight itself is an L-shaped plate, with the windage screw passing through it and an aiming aperture in each of the flat plates. Rotating the sight adjustment plate turns the threaded shaft, and the sight moves right or left along the shaft.
The L plate of the sight can be flipped so you use one or the other sighting aperture. The two apertures are the same size, but one of them, the one with an “L” marking, has the center of its aperture higher above the adjustment shaft than the center of the other one. This is the long-range aperture, hence the L.
This was the height of military aiming technology, circa 1969. Gone was the click-adjustable rear sight of the M14, derived from that of the M1 Garand. Unless you want to be plinking at sandy hillsides out past 350 yards, you will have no need of the L sight, and will do all of your work and aiming with the other aperture.
Vertical adjustments will be made with the front sight.
Once the A1 sight is zeroed, you do not make sight adjustments while firing. That is, if you find you are dealing with a wind from the right while shooting at your target 200 yards away, you will not be turning the adjustment plate. You will have to hold off, that is, into the wind.
Our fathers and grandfathers fought with rifles (this is an M1 Garand) that had adjustable sights worthy of a target rifle. That’s what the USMC wanted to get back to when they pushed through the A2 improvements.
The A2 is click adjustable for windage and elevation, but it requires that once you have zeroed your rifle, you have to re-adjust the sight adjustment wheels so you have a zero starting point. More in a bit. The sight apertures themselves differ from those of the A1. The L plate of the sight still rides on a threaded shaft, and moves when the adjustment wheel is changed. It also flips up so you can use one or the other. However, the sight apertures are markedly different.
There is a large one, marked “0-2,” and a small one. Many new shooters assume that the large aperture is your aiming aperture for shooting from zero to 200 yards. Close, but no cigar. The 0-2 aperture is meant to be used as an aiming device in low-light, night-time or bundled up in chemical protection situations. It’s not a regular-use out to 200 yards sight.
You will zero your rifle using the small aperture. Unlike the A1 sight, the centers of the large and small apertures of the A2 are intended to be the same distance above the adjustment screw. Thus they will have the same POI. Given the vagaries of mechanical fabrication and human eyesight, they are close, but not always exactly the same. Plus, the larger aperture produces a larger group on target, at any range, and with any ammo, than with the same ammo at the same range using the small aperture.
So, zero with the small aperture and leave it set to the small aperture, unless it is so dark you need the larger aperture. (And I have to ask, if it is that dark, what are you doing shooting?)
How iron sights work
If you have done any handgun shooting, you know the way those sights align – top edges level, front blade centered in the rear notch, and the bullet will strike at the optical top center of the front blade. Rifle sights of the same design work the same way. The aperture sights of the AR do not.
To aim, you look through the rear aperture. If you relax and let your brain work without overly supervising it, it will find the optical center of the aperture. Now place the tip of the front sight in the center of the aperture, with the protective wings (if you can see them) evenly spaced on the right and the left.
Now, place this whole assembly on your target. The bullet will strike at the tip of the front sight.
The smaller the aperture (because it is smaller, or because you have positioned your face further away and made it appear smaller), the smaller the group you can shoot. But also, the slower you shoot, simply getting things lined up. The larger the aperture, the faster you can shoot. If you expand aperture size, you reach an aperture diameter so large your brain can’t precisely determine center, and you then shoot bigger groups than you would otherwise.
With practice, the aperture sight can be very fast and very precise.
A bit of mis-alignment of the rear sight in its housing is not cause for alarm. If you have to crank it all the way over, front sight housing work may be called for.
They do, however, have some drawbacks. Your eye can only focus at one distance at a time. Your brain can only have one center of attention at a moment. It can, however, perform some operations automatically, if they have been practiced enough to make them semi-autonomous. (This is not multi-tasking, it is simply shuffling through the operations fast enough to be close enough.) But you can still only focus at one distance.
So, the act of aiming has your eye bouncing back and forth – between target, front sight, rear aperture, sight, target, and so on. The classic teaching aid is to tell the shooter to “focus on the front sight, make it sharp, and let the target and rear sight fuzz out.” This works well when the target is a stationary, distinct and non-threatening piece of paper or cardboard. In the real world, you have to spend at least some time on the target, if only to determine where it is and that it still qualifies for target status.
Learning iron sights isn’t easy, and can be quickly forgotten.
The red-dot sight began with the Aimpoint back in the very late 1980s. It appeared in the U.S. in competition at the 1990 USPSA Nationals, on the pistol used by Jerry Barnhart. The first reaction was, “No way will that work.” After Jerry cleaned everyone’s clocks, Doug Koenig had one on his pistol a few months later at the IPSC World Shoot, where he became world champion.
As soon as national-level 3-gun competition began, rifles had red-dots on them. They were derided as “impractical” and “not real combat gear.” In the beginning, yes. But the reliability imperative of practical shooting competition (your gear is your problem, once the clock starts, and if it fails you do not get a do-over) meant all competitors using them were always looking for more reliability, durability and utility.
By the second Iraq war, red-dot sights had been adopted and proved their usefulness. It was mildly amusing, seeing photos of M4s in Iraq, rifles that were equipped to have made decent but not match-winning Open class 3-gun rifles back in the 1990s.
Red-dot sights work by projecting a red dot, reticle or other pattern onto a screen inside of a tube or housing. The miracle of optical physics presents the dot to you as if it were on the same optical plane as the target. That is, it appears to be “out there” and not a dot a few inches from your face. This means your eye has only the one focus job, dot and target together. Your brain has only two things to deal with, dot and target.
You place the dot on the target and press the trigger.
But wait, there’s more goodness: the dot is, essentially, parallax-free. That is, if the dot appears to be at the edge of the field of view, the bullet will still strike at the dot. Moving the dot does not change the agreement of dot with bullet.
A red-dot sight, like this EOTech, can also be teamed up with a magnifying adapter, and thus get you the best of both worlds.
The bad news is simple, dots need batteries.
Magnifying optics were not new when they began to be adopted on rifles in the trenches in WWI. Since then, they have increased in durability, light-gathering, clarity and reticle designs. What they do is let you see better, but not necessarily shoot better. The choice of magnifying optics comes down to a matter of balance. That is, size and weight against increased magnification and fragility. Increased performance increases cost, where a top-grade scope can cost more than the rifle it is mounted on. And with variable scopes, there is a need to shift from one power to another, as any extreme is useful only for a specific puropse. A 3-9X scope is great, at 9X, if you are shooting at something at extreme range. Let a target of opportunity pop up ten yards away, and 9X is very much the wrong power to be on.
You should do all your zero work from a solid bench, with supports such as sandbags, or prone, with sandbags or supports. You cannot zero a rifle shooting offhand. No one is that good.
To start, shoot a five-shot group. Measure closely the distance from your aiming point to the center of the group, and consider how much adjustment you need to move the group to the aiming point. When we do this in classes, it can take forever. Some shooters have rifles already zeroed. Some don’t. And some take several magazines of practice to shoot a group smaller than the target paper, typically a target run off of a copying machine.
The USMC bought truckloads of the Acog, and did good work with them over in the various sandy places of the world.
Optics need not be expensive. This Millet DMS-1 is plenty good enough, and won’t break the bank.
If you need to make a correction, make it. Don’t do half the estimated number of clicks, do them all. Then shoot again.
When we have had the instructors zero rifles (at least enough to make sure they are close), the instructors will shoot two or three, make a full correction, and shoot two more. We’re often “in the circle” (the circle used for the desired zero setting) in five shots. Sometimes it takes more.
The different zero settings go by a variety of names, but what I use are 100 yard, 50 yard and 25 yard zero. All my calculations will be done here with a 55 grain fmj bullet, at a muzzle velocity of 3100 fps. Changing bullets will change the trajectory in minor ways, but this will give you a good grasp of what a zero is and what it does. For instance, those of you with SBRs will find the drop to be greater, since you’ll be starting off with less velocity. Those who can afford the Mk 262 load, with 75 or 77 grain bullets, will see less drop, as the bullet has a larger ballistic coefficient than the lowly 55 fmj.
Here’s how they work.
Use the small aperture on an A2 sight, or the unmarked (not the “L” aperture) on an A1 sight.
Use your twenty-five yard zero target and adjust your sights so the group is an inch and a half below the POA. The result is that the bullet will still be rising up to 100 yards, where it will reach its maximum height, and ride close to the line of sight for about ten yards before starting downwards. At 200 yards it will be 2.23 inches low (a convenient memory aid) and at 300 yards it will be a foot low.
So what you have is a zero setting where, from the muzzle to 200 yards, your bullet is never more than the differential between the line of sight and the parabola of the trajectory, and the bullet is always below the line of sight when they differ. Inside of 200 yards, you are not more than two and a half inches off. And out past two hundred yards to three hundred, a high center chest hold will get you a solid hit on a miscreant.
This zero has the benefit of being simple and straightforward. You have a close association of the line of sight with POI, and at no time is the bullet above the line of sight. The 100 yard zero is the one method where there is only one crossing, one point where the line of sight is crossed (or in this instance, met) by the trajectory.
All the other methods have the trajectory crossing the line of sight twice, the near zero and the far zero. All the other methods also have details between the A1 and the A2 that you have to attend to.
In this process, the zero target is again at twenty five yards. Here, the point of aim is at twenty-five yards, and the point of impact there is 1.2 inches low. The result is an improved medium-range trajectory.
At fifty yards, the bullet is at zero. At one hundred yards, the bullet is now 1.6 inches high, an amount that could only be seen or used through a magnifying optic. Iron sight and red-dot shooters won’t notice a thing, unless they are very good, and shooting from a supported prone. Between 130 and 150 yards, the bullet will be 2.0 inches high, as high above the line of sight as the bullet will get.
At two hundred yards, the bullet will still be half an inch high. That is more than even the magnifying optics users can see.
At 300 yards, the bullet is now 5.9 inches low.
Here, point of aim and point of impact are the same at 25 yards. The results are dramatically different. At 100 yards, the bullet impacts 6.3 inches high. Roll that around in your head for a bit, half a foot over your point of aim.
At 200 yards, the bullet is ten and a half inches high.
At 300 yards, the bullet is still eight inches high, with the crest of the parabola having been reached just a bit past the 00 yard markers, at 1.6 inches in height over the line of sight. The bullet does not come back down to the line of sight until 385 yards.
In the vernacular; what the frak?
The 25 yard (or in military use, 25 meter) zero is meant to replicate the trajectory of old, the rifles of yore. The intent was simple, a century-plus ago: use the belt buckle on the enemy soldier as an aiming point, and you will get an abdomen or chest hit all the way out to 400 yards. Clearly, today, no one will stand still, or even move in the open, with 400 yards of clear space between them and the enemy. Plus, we aren’t in a military context. I’m not sure you can coherently describe a situation where you need to be shooting at someone 400 yards distant with a rifle.
For the longest time, I used the 100 yard zero. It presents an easy and straightforward system of aiming. At close range, hold off to account for line of sight. Beyond twenty-five yards, out to as far as I plan to ever be shooting people, line of sight and point of impact are closer to each other than the group size I’m likely to shoot.
However, the 50 yard zero does have some advantages, if I plan on shooting in matches with rifle stages beyond CQB distances.
With the100-yard zero, your bullet will strike the target well below the point of aim.
With the 25-yard zero, the point of aim and the point of impact are the same at 25 yards.
The 50-meter zero moves the initial point of impact up, as well as pushing out further the second point the trajectory crosses the line of sight.
Here is a zero target, with the first and second groups on it. This upper came off the bench pretty close to being zeroed as-is.
Here, on one target, you see the effect of moving closer, which moves the point of impact lower and lower below the point of aim.
25 yard zero? No use for me, at least none that I can see for now.
Now, if you use a solid bench and a rest to shoot from, or shoot prone with a sandbag support, you can get very well zeroed. Even an average shooter, with indifferent ammo and a rack-grade rifle with iron sights and not-egregious trigger, should be able to shoot a group of one inch at twenty-five yards. A good shooter, even with irons and a good rifle and ammo combo, should be able to shoot five shots that touch.
The best should be able to shoot a one-hole group.
Once done, go to the 100 yard line and verify. Don’t shoot just one group and adjust. Do several and take the average, or take the last half of more than a few groups.