You have a new AR15.  And now that the frenzy is over, and you know that it will be at least the next Presidential election until you can barter with it for someone’s store of fresh water and beans, and you figure you want to shoot it.  Good.  It’s a shooting tool that needs to be used for it’s purpose.

But how do you use one of these things?  Maybe you’re new to the platform, or maybe you’re just new to shooting in general.  Let’s talk about some of the basic things that you’ll need to know in order to put your rifle to use.

First, the physics.  Bullets fall from the moment they leave the barrel.  If you drive a car off of a flat pier, it will eventually fall into the water.  If you drive it faster, it will get farther, but it will still begin it’s downward trajectory the second it leaves that barrel.  So too with bullets.  So, with a bullet that falls as soon as it leaves the muzzle, how do we make it go as far as we want it to?  We lob it.  Just like a football.  The farther we want it to go, the more we lob it into the air.

Zeroing a scope is nothing more than adjusting the sights to allow the bullet to lob more or less into the air – and then it doing that in a controlled way every time.

Here’s an illustration that I took from someone over at M4 carbine.net:

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Armed with this information, let’s consider that if we lob the bullet from the end of the muzzle, and it flies in a parabolic trajectory, then the bullet crosses the plane of the scope twice: once on it’s way up, and once on it’s way down.  How far apart those two crossings will occur depends on both the bullet weight, and the bullet trajectory.  For our purposes here today, let’s narrow the conversation to the most popular AR15 bullet: the 55 grain M193 round.  This will give us our constant in a world of variables.

First, you need to examine what you want to use your gun for.  Are you going to be dialing in on some long ranges?  Are you going to be clearing your house and never shooting past 50 yards?  Are you going to be stretching it out to 300 or 350 for a coyote, while also wanting to have a good handle on anything nearer to you in the 75 yard range?  These are different guns that you’re wanting, and you’re going to have to figure out what you want your gun to be good at.  Let’s look at some zeros:

The 300 yard zero.

The 300 yard zero is the Marine Corps zero.  It is a very good zero, if you understand that between 36 yards and 300 yards, you have a bullet that is going to hit above your point of aim, sometimes as much as nearly 5 inches!  I’ve missed quite a few coyotes and hogs at 150 yards, because I wasn’t aiming below them.

If you want your rifle to come back down and meet your crosshairs at 300 yards, you need to first sight it in at 36.  Now, as with all of these zeroes, you need to actually push your gun out to 300 yards and confirm the zero and make your final adjustments, but if it’s right on at 36, it will be close at 300.

The chart for the 300yard zero looks like this:

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You see that the barrel begins 2.6” below the line of the scope.  The bullet is lobbed up to cross the path of the scope at 36yards, and then it comes back down again at the 300 yard mark.  This let’s you reach out a long ways with the gun (300 yards is a long distance to shoot at a small coyote) with consistency.  Just remember, the big deal with this zero is that at 175 yards, you have to aim 5 inches low, in order to hit where you want to hit.  You need to be somewhat proficient with range estimation to use this zero.

The 100 yard Zero

If we lob that bullet so that the top of the parabola is hitting the line that the scope is looking down, the bullet only touches that path 1 time.  This is a very simple solution to not having to decide when to shoot under or over a target, as you will only ever have to adjust upwards as your bullet gets farther and farther away.

Here is the chart for the 100 yard Zero.

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You can easily see that to shoot a coyote at 300 yards, you’d have to raise the crosshairs 15 whole inches!  And if you misjudged him by 25 yards, and that coyote were really 325, you would miss him by 5 inches.  That’s not the sort of zero you would use on your gun, if you plan to use it out to 300 yards.

It IS however, the sort of zero you might use, if you only plan on using that gun inside of 200 yards.  You see that the bullet is always inside of a 2” bulseye as long as it’s within 200 yards.  That’s a great group at those close ranges, but let’s be honest,

The 225 Yard Zero (or the 50 yard zero)

I like this zero a lot.  If you sight it in at 50, it is back on at 225.  At the height of the trajectory, it’s only ever 2” high at any time.  Now, your bullet is not going to be anywhere near the ballpark when you get to 300, but it’s a pretty good medium distance zero.

Here’s the chart on that one:

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And a graphic representing the various options:

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Now that you’ve picked which zero will perform best for you, a few pointers before you go off and start shooting your rifle.

First, You may have a rear sight that adjust for specific yardages.  The KAC 600 meter sight is a very popular sight that I use on my rifle.  The Matech rear sight is also a popular one.  The KAC sights can be had right now on ebay for around 50$.  This is an incredible deal as they usually sell for around $175.  The Matech rear sights can be had for somewhere around $35.

These sights have adjustments on the rear sight to allow the user to quickly dial in a range, and expect the bullet to be there.  The way to sight these in is a little different than if you have a regular sight.

First, you put the sight on the Z.  This stands for zero.  Zero the rifle at this marking.  You do this by ADJUSTING THE FRONT SIGHT UP AND DOWN until you are hitting where you need to, and only touching the rear for left/right movements.  Sight it in at 36 yards on the Z.

For the MATech rear sight, turn it to the 300 yard mark.  Now, zero at 25 yards.  Now, all of your adjustments will work.

Adjusting the front sight is done through depressing the button just on the muzzle side of the post, and rotating the post.

You always move adjustments, whether it is on a scope or a sight, in the direction that you want the bullet to travel on the paper.  So, if I am missing low and left, I need to adjust the sights up and right.  These directions will be indicated with markings on the sight itself.

I hope you get some good out of this.  There is nothing that inspires confidence in one’s firearm than knowing the gun is on.  Go spend some concentrated time just working with your gun.  Every rifle will be a little different depending upon ammo, barrel length, atmospheric conditions.  What I have given you above are generalities that will be very close to most guns, but probably not exact.  There is no chart, and no substitute, for knowing your gun.

The AR15 platform is surprisingly versatile and impressively accurate for a short, mass produced firearm.  It is perfectly capable of holding a 3” group at 100 yards, and many times much better than that.