Nikon BDC Reticle Scope
After picking up a new scope for your AR-15 you’re going to need to sight it in before it will be able to make your shots any more accurate. The good thing is that this is any easy process, we’re going to show you how in our quick guide.

If you were to just unbox a new scope, mount it on your rifle, line up the corsshairs on the bull’s eye of a target 100 yards downrange and pull the trigger, there is a slim chance that the bullet actually hits there.

That’s because where the scope is aiming and where the bullet travels are not synced up with each other yet.

Sighting-in or “zeroing” is the process of calibrating your scope with the rifle bore so that the placement of your crosshair actually represents where the bullet will hit the target.

A bullet’s trajectory is always subject to where the barrel is aiming, that’s a given. The bullet simply follows the projectile motions of any external ballistic.

As the bullet is propelled out from the barrel the effects of gravity and drag also play part in where it will go.

Since the bullet’s path is (relatively) constant between shots, it is then up to us to adjust the scopes positioning so that the sight line matches the position of the moving bullet downrange.

And since the bullet has vertical movement as it travels, that means we have to sight-in at a specific distance that we want our scope to be accurate for.

There are a handful of different schools of thought on how to sight in a rifle scope, but we’re mainly concerned with doing it as accurately as possible using the least amount of ammo.

Here are the basic steps to follow:

Step 1: Gather Your Materials

When zeroing your rifle scope one key aspect is keeping the rifle in a steady position so we know that any differences between shots are due to the scope and not the position of the gun.

For this you’ll need access to a rifle bench to shoot from. This provides you a sturdy support to take more steady shots. To help with this you’ll also want to use either sandbags or a rifle clamp for additional support.

Have access to any adjustment tools that you’re scope requires. While some have thumb-adjustable turrets, others have slotted screws that require a tool.

Make sure to bring the specific ammunition you want the rifle to be zeroed for. Different ammo types have different trajectories due to load size. If you were to sight in with one ammo type and then try shooting with another, the zero wouldn’t hold.

Bring a shooting target. You’ll want to use one with discernable aiming spots on it. You’re standard paper target will do just fine.

Step 2: Bore Sight at 25 Yards

Bore sighting is the most basic way to get a “quick and dirty” pre-alignment of the barrel and the scope which makes the zeroing process much faster.

The goal is to align the crosshairs of the scope with where the barrel is pointing, which we will refine later.

The reason we do this is because the initial mounting of the scope may be pointing so far off from where it should be that for any shots we take we would not even be on the target, making it impossible to know what corrections to make.

Especially at a close distance of 25 yards it should be an easy process to make sure that the bullet is landing on paper when we aim at the target.

For an AR15 the easiest method is visual bore-sighting, which doesn’t require a laser bore-sighter. To do this, first you’re going to have to separate the upper receiver from the lower receiver and remove the bolt carrier group. This will let you look down the barrel from behind the rifle.

Put the upper receiver on the rifle bench and secure it with sandbags or a clamp. Now look through the barrel and line it up with your target that’s at 25 yards. You can’t get too accurate with this so just get as centered as you can.

Now, without letting the upper receiver move from that position, use the scope adjustment to center the reticle on the target. Take a few looks between the two to make sure they’re both still aimed appropriately.

Go ahead and reassemble the gun and take a shot at the target using the scope. If all went well you’ll be hitting part of the target. It may not be exactly where the crosshair is aimed but we’re going to refine this. If you’re way off repeat the bore-sighting process before moving on.

Step 3: Take a Shot at 100 yards

After bore sighting move the target out to 100 yards. I find this to be a good zeroing distance for AR’s. If you’re doing bigger game hunting and plan on taking longer shots, start with the 100 yard zero and then move it out further.

Set up on the bench and line up your crosshairs with the center of the target. Be sure to get good and steady. What we want in the process is repeatability between shots. So it is crucial for the best zeroing that we have our crosshairs fixed at the same point every time.

When ready, fire a shot. You’re bore sighting should have been good enough so that you hit somewhere on the target at 100 yards. If not you’re going to have to bore sight again, this time with a little more care. But if you’re able to see where you’re bullet hit, we’re good to move on.

Step 4: Make Adjustments to the Scope

So where did your bullet hit? Most likely not the bull’s eye, but that’s okay. We’re on the right track as long as it’s on paper. The scope is still slightly out of alignment with the bullet trajectory, so we’re going to have to adjust it using tools if necessary, or the turrets.

The gun position was probably altered from the recoil of the first shot, so reposition it again so that the crosshairs are on the center of the bull’s eye. Now, the crucial part here is to make sure the gun doesn’t move at all from this position when adjusting the scope.

This is where the rifle clamp or sandbags come into play. Being careful of moving the gun, adjust the windage and elevation of the scope until the crosshair is now centered on the point of impact of the first shot. This is called “walking it in”.

If you were unable to hold the gun steady, you could also have used you’re knowledge of how much minute of angle (MOA) each click of the turret corrects your scope at 100 yards. Most scopes have a 1/4 MOA, meaning for every click the scope crosshair is moved a .25″ at 100 yards.

If you can estimate how far off from the center of the target your bullet point of impact was in inches, you can compensate for that with the right amount of turret clicks.

Step 5: Take Another Shot at 100 yards

After making these adjustments, re-aim at the center of the target, and take a shot. If all went well your shot should hit exactly where it’s aimed. Fire a 3 round group to confirm.

If it is still off the mark then the gun probably moved slightly as you were adjusting the scope. Follow the same steps of aiming at the crosshair, keeping the gun steady, and adjusting the scope to center on the latest bullet point of impact.

Congrats, you’ve learned how to sight in a rifle scope. Repeating the process for different distances, or any time you think your scope has become un-zeroed, enough times will make the whole ordeal get simpler.

Have a better method? Share your wisdom below.