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How to Mount a Scope on an AR15: Ultimate Step-by-Step Guide

How to Mount a Scope on AR15

Some would say, how to mount a scope on an AR15 is the challenging part. But in reality, the tricky part is making sure you hit the right alignment between the bore and optic.

Imagine, after spending hours mounting the riflescope, you then head out to the shooting range to test it, only to find out that the precision of your AR 15 is off by a few centimeters.

You’ll have to remove the optic piece from your AR 15 again and start the whole process over. Frustrating, right?

Worry no more as everything you need to know is in this article. We’ll give you a guide and some tips to help minimize errors when you mount a scope on an AR 15.

Necessary Tools to Mount a Scope on an AR 15

Necessary Tools

It’s crucial to prepare the following tools before you start.

Whether you plan to make use of scopes with traditional rings on a bolt action rifle, a Weaver-style rail system, or a one-piece cantilever scope mount, the process would require the same tools. 

We have listed the essential tools below. You may opt to substitute some with the regular ones.

It would be possible but there’s a need for extra caution as it might damage the optic piece of your AR 15 in the process.

You’ll need:

  • Torque wrench
  • Bubble level
  • Hex bit tool
  • Scope or cantilever mount

Nice to have:

  • Rubbing alcohol
  • Cleaning patches
  • Loctite (optional)
  • Gun vise or shooting rest

Once you have all these in an arm’s length, let’s get to work and start the mounting process.

5-Step Process to Mount A Scope on Your AR 15

We’ve narrowed down the whole process to 5 steps. Some tips and reminders are also included so be sure to read carefully and follow all instructions to avoid any chance of failure during or after the process.

As you’ll be working with small or fragile materials, you’ll also need a lot of patience, especially if this is your first time to mount a scope. Read everything twice and take one step at a time.

Step 1: Prepare AR 15

Step 1

We highly recommend having a gun vise or shooting rest to help you keep your AR 15 in place.

When the gun is secure on the shooting rest, be sure to unload your rifle and remove the magazine. Use the cleaning patches and some rubbing alcohol to clean the equipment and screws. 

Wipe the excess oil from the components and the rail. When you’re done cleaning, use the bubble level as a guide for you to achieve the right level setting. Make sure to do this before proceeding.

Step 2: Attaching the Scope Mount

Step 2

Once the rifle has the right level setting, grab your rifle scope and place it above the upper receiver.

Do not put the scope mount on both the upper receiver and free-floating rail. Avoid doing this at all costs for this may cause unnecessary pressure on the tube.

When the scope is mounted onto the receiver, you can start to tighten it using your hand. The objective is to make the scope balanced and stable, but not too tight with your torque wrench.

Using a torque wrench, further tighten the scope mount.

For complex scope mounts, be sure to double-check and read the manual on scope mount instructions provided by the manufacturer. Each one has a different torque level so be sure to pay close attention and not overdo this.

Step 3: Adding the Scope

Step 3

Now that we have the scope mount, the next thing is fixing the optic piece in the rifle.

Take note of the rings – these should sit on the flat surface of the scope. Take the optic onto the mount. Put the top of the scope rings over the optic to secure.

Take your hex bit tool and tighten the screws to about 80%. Make sure to follow an X pattern while doing this.

Make sure that each side of the rings should have the same gap level before you fully tighten them.

You’ll know that this is done correctly when there is a small space available for the optics to move. Once you’ve tightened the scope rings and checked the gap for the optic piece, you can check the scope.

Test the rifle scopes eye relief with open eyes.

Note: Eye relief refers to the distance held by the shooting eye from the back of the scope which helps the shooter see the entire image produced by the scope.

In case it feels off, adjust it to a comfortable position for you until you have a full field of view with your eye relief.

Step 4: Leveling

Step 4

This is the crucial step in determining the accuracy of your scope mount.

Take your bubble level again and place it on the flat part of the rifle tube. Make sure that the AR15 is level as well. Again, this is where the shooting rest or gun vise comes in handy.

Before you can bubble level the scope, the reticle should be properly aligned – both vertical and horizontal levels. You can manually do this by identifying a target from afar. 

As a second measure to check, use a door frame as a reference. Make sure the door frame is vertically verified with your level.

The reticle should meet both angles or lines in the door frames. The sight from the reticle should seem natural, with no uneven or distorted views.

Step 5: Securing Scope Screws

Step 5

Once everything is leveled correctly, it’s time to tighten the scope rings.

Again, keep in mind the X pattern when tightening the screws using the torque wrench. Both sides should be evenly screwed so as to not mess up the leveling or ruin the scope mount.

There you have it! Your AR15 is now equipped for long-range shooting. All there’s left to do is to test the precision of your rifle.

Frequently Asked Questions

Frequently Asked Questions

#1 What Is Scope Ring Lapping?

Lapping the scope rings is highly suggested, especially if you are planning to do long-range shooting. This process is best done by a gunsmith. It refers to the process of making the inside of the rings even by sanding them down.

By lapping, the rings would hold a better fit to the scope. It is not recommended to do this on your own.

There’s a high chance that one may overdo the lapping or have uneven sides. Worse, you might ruin the rings which would be an added expense.

Scope ring lapping kits are readily available but they do not come cheap. It would be more cost-efficient to take your rifle to a gunsmith to have this service done. This would improve the accuracy of your optic piece.

#2 What Are Cantilever Mounts?

A cantilever is a unit consisting of a one-piece base and a ring.

It’s the only mount system that leaves no room for error during the mounting process. No extra screws or separation is required. It’s the easiest among other available scope mounting system designs for AR15.

Conclusion

Conclusion

To aid you in mounting the scope, check the level of your optics and rifle every now and then using a bubble level. It’s a small step that can save you a huge amount of time afterward.

You may want to consider investing in a shooting rest. It’s the safest way to hold your rifle in place during the installation or cleaning process.

That’s all you need to know about mounting your scope on an AR 15! If all steps are followed, there shouldn’t be a problem with the accuracy of your scope mount.

For good scope choices for your AR15, check out our articles on the Most Affordable 1 6x Scopes and Best Scopes for the 300 Blackout.

About the author

Christopher Wade

Christopher Wade is a true outdoorsman. After spending most of his career as a firearms expert and instructor in Nebraska, he retreated to the great outdoors to enjoy retirement.

Christopher’s expertise in handling firearms and hunting gear are what propelled him to create the Shooting Mystery blog. He hopes for all readers to gain useful and practical knowledge for enjoying their time outdoors.