How to Zero Your Rifle Scope

If you’re lucky enough to have purchased your AR15 with a scope already mounted on the upper receiver, it’s a safe bet that the optic system has been bore-sighted and zeroed in at the factory.

In the world of DIY budget builds, you are, in essence, the factory, so knowing how to bore-sight and zero whatever optic system you mount on your AR15 is not only necessary, but also a required skill set you need to learn.

There are typically three parts or activities you’ll need to get familiar with after mounting your scope – bore-sighting, choosing your zero range, and zero in the optics, and you’ll want to exercise these activities in the proper order for optimum effect.

Bore Sighting

The first of these exercises is almost like dry firing training, except you’re removing your upper receiver from your lower and locking the upper receiver in place. At the same time, you aim at a paper target twenty-five yards away.

Before you attempt bore sighting, you need to take proper care to ensure you’ve correctly installed your scope on the upper receiver in the first place. If your optic system gets jiggy during bore sighting or when you try to zero it in, you’re going to need to perform all the actions again.

Your scope should be mounted where it provides three to four inches of eye relief and the windage turret or adjustment knob on the right side of your AR15. If installed right, the reticle, more commonly known as the crosshairs, should be aligned to the rifle’s bore at a ninety-degree angle.

 

Think of bore sighting as the rough draft to more precise zero adjustments to your scope. One of the primary differences is that typically you’ll need to break down your AR15 so that you’re only working with the optics you recently attached to the upper receiver.

A word of caution here. If you’re attempting to perform these steps at your local firing range, be prepared for the chaotic sounds of people popping off rounds to the right and left of you. A place out in the country where you can assume a prone position or fix your upper receiver into a base of sandbags works better.  

Once you’ve broken your AR15 down, place the upper receiver in a secure position point at a target no more than twenty-five feet away. Be sure to remove both turret covers and put them somewhere where they won’t turn up missing. The pocket of your pants or jeans is the best place for them.

This next step requires a little artistic motivation, so if you’re incapable of drawing a straight line even with a ruler, you may want to get one of your colleagues to create a bull’s eye for you. Have them make one about the size of a quarter on a large cardboard box or crate and place it about twenty-five yards downrange.

Once your colleague has rejoined you, look through the barrel and adjust the upper receiver until the bull’s eye is directly in the center of the barrel. At this point, you’ll want to lock the receiver into those sandbags, so it won’t move. If doing this by hand and in a prone position, get someone to assist.

Next, and without moving the upper receiver, you need to peer through the scope and sight in on the bull’s eye. If the crosshairs or reticle is precisely in the center of the target, you’ve got a clean boresight on the first try. Most of the time, you’ll not be that lucky, and the crosshairs will hardly be close, but that’s okay because it will get on target when you and your helper perform the following exercises.

Again, make sure you’re not moving the upper receiver as you do this, but call out the number of clicks required to your colleague on the elevation adjustment until the crosshairs are on the same level as the bull’s eye vertically. Perform the same process with the windage turret until the crosshair is precisely in the center of the bull’s eye.

Once that’s done, you can celebrate a little because you’ve effectively bore-sighted your rifle. If you want confirmation that you did it correctly, reassemble your AR15 and fire three rounds aiming for the bull’s eye, of course. If all three shots at least hit somewhere inside the target, your bore sighting efforts were successful, and it’s time to move on to the finesse part.

 

Choose Your Zero Range

Typically, the most common zero range is 100 yards, but it may differ depending on the shooting you often perform. If you’re a long-range hunter and most of your shots are in the three or four-hundred-yard range, then a one-hundred-yard zero range will not work very well.

Conversely, if all your shots during deer hunting season happen from a stand forty yards from your food plot, a hundred-yard zero won’t work either. If you sometimes do both, then split the middle and choose a two hundred zero range.

After a successful bore sighting, and if your location allows it, place that target down range at two hundred yards and get ready to do a little mathematic problem-solving.

Suppose you’re lucky enough to fire three rounds without one flying off and missing the target entirely. In that case, you need to triangulate the shots of your shot pattern and measure the distance from the center of your triangle to the exact center of the bull’s eye.

As an example, let’s say the center of your shot pattern is three inches low and four inches to the right of the center of the bull’s eye.

Since almost every optic system these days has adjustments that move the crosshairs a quarter of an inch at one hundred yards, you’ll need to adjust the scope accordingly based on the number of inches determined by your triangulation.

For this example, if you’ve chosen one hundred yards as your zero range, you will need to rotate the elevation turret twelve clicks to move the crosshairs three inches up and the windage turret sixteen clicks to the left.

Once your zero-in efforts are complete, it’s all about verification and fine-tuning until you start punching out the bull’s eye consistently. When you begin to paint your targets with shot patterns that go precisely where the crosshairs indicate, it will always be an exciting day for any AR15 rifle owner.