This writer has been in the armed forces for quite some time. During his tenure as an NCOIC, he ran more than a few zero and qualification ranges. He continues to witness trained soldiers and civilian “cool guys” alike cock up their AR 15 zero. So let’s clear the air, here. Today we’re going to teach you how to properly zero and co-witness your AR 15 so you can stop wasting ammo and hit paper.
But before we do that, it’s important to understand the fundamentals of zeroing a rifle. Otherwise, you’re just doing what this writer’s telling you to do without understanding how the process works. Believe us, he’s tired of dealing with that in the military.
How a Rifle Zero Works
Zeroing your AR 15 – or any rifle or handgun, for that matter – means adjusting your point of aim (POA) so it matches your rifle’s point of impact (POI). There are many ways to go about this, and not one single method of zeroing is necessarily right or wrong (as long as your POI and POA line up at the end of it all).
We’ll clue you in on a little secret: The military’s method of zeroing the M4 and M16 is not the most effective, accurate, or intuitive method. It actually results in a more unpredictable bullet trajectory, depending on the distance you’re shooting. That’s because the military zeroes their rifles at a measly 25 yards, with the intent of hitting targets at 300 yards. Makes no sense, but we’ll explain.
First, let’s explain what happens when you fire a rifle and try to zero it, so you can understand why this is not ideal:
See this graph? That dotted line represents your bullet trajectory if you were to fire your AR 15 on a horizontal plane. When you zero your rifle at a fixed distance, like 25 yards or 100 yards, you’re adjusting your rifle’s barrel so it points upward. This allows your iron sights or optic to be horizontal, so you can look at your target. All the while, your barrel is “lobbing” your bullet into the air so it can come back down onto your target.
See that figure above? Notice how the barrel is pointed upward, while the optic is level with the target? That point at which the optic’s picture (the target) and the bullet drop meet is where your POI and POA meet – that’s the goal of zeroing your weapon, to make those two points meet.
Now we can explain why zeroing your AR 15 at 25 yards is a bad idea. The average AR 15’s iron sights or optic of choice sit about 1.5 inches above the barrel. That means at 25 yards, you must crank down your sight’s adjustments so much that you’re compensating for this angular difference. At such a short distance, that difference is huge.
This leaves your barrel pointed up at a more extreme angle and it leaves less room for adjustments when you want to hit longer distances. This causes your bullet to actually rise a fair amount when you aim at targets – often, your rounds can impact so high that they miss your target or paper completely, and now you have no way to adjust because you can’t witness your impact.
Zero at 100 yards!
The Army zeroes at 25 yards for a few reasons, But mostly, they do it because it’s easy and convenient. It does no good for accuracy. When you zero your AR 15, you should zero at 100 yards. This reduces that angular difference between your barrel and sights, making shot placement more consistent across all distances.
If you're shooting for accuracy, a 16" stainless barrel will offer MOA groups at 300 yards, providing just 12" of drop using a 100-yard zero
Zeroing at 100 yards does take a bit more patience and practice than a shorter zero distance – after all, many shooters can’t hit 100-yard groups consistently. But it’s worth the investment. The AR 15’s trajectory is relatively flat, out to 200 yards.
Beyond that, your bullet drop is only a few inches at 300 yards. This is all thanks to the fast and lightweight profile of the .223 and 5.56. In short, there is no need to zero at 25 yards. Take an expert's word for it. Zero at 100 yards.
How to Zero at 100 Yards
That’s easy! Remember how zeroing at 25 yards isn't intuitve? At 100 yards, it’s super easy. One MOA is 1” at 100 yards. Nearly every optic and iron sight on the market for the AR 15 features ¼ MOA adjustments. That means if you’re shooting 1” to the right, four clicks to the left is all you need. There is no math or converting numbers.
Most sights provide decimal MOA adjustments, which can abe confusing at 25 yards, 50 yards, or more than 100 yards. Magpul's rear sight offers 0.5 to 0.7 MOA, while its front sight offers 1.2 MOA. The 100-yard zero makes conversion easy.
Hitting 2” high? That’s eight clicks down. Shooting a quarter-inch with your final group? One click up to fine-tune is all you need. This method of zeroing is intuitive, easy to understand, quicker to finalize, and it affords you, the shooter, with the most versatility across the longest effective range. Now you know how, and why, to properly zero an AR 15.DISCLAIMER: If you are new to the world of DIY gun building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. At 80 Lowers, we are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.