So, you’ve got your AR-15, a shiny new optic, and you’re ready to improve your accuracy. But there’s a small, fixed obstacle in your way—the front sight post. You might be wondering if that iconic A-frame sight will be a problem. The good news is that mounting a scope on an AR-15 with a front sight is not only possible but also a very common practice. The key is understanding how your optic and your sight will work together, or more accurately, how your brain will learn to ignore one of them.
This complete guide on How To Mount Scope On AR-15 With Front Sight [Complete Guide] will walk you through everything you need to know. We’ll cover the important concepts, the tools you’ll need, and the step-by-step process to get your scope securely mounted and properly zeroed. By the end, you’ll see that the front sight is less of a problem and more of a permanent backup, and you’ll be confident in your ability to complete the installation yourself.
How To Mount Scope On AR-15 With Front Sight [Complete Guide]
Before you grab your tools, it’s crucial to grasp a fundamental optical principle. When you look through a magnified scope, the focal plane is set to a specific distance, typically far away. Your front sight post, being much closer, will appear as a slightly blurry shadow in the bottom of your sight picture. At higher magnifications—usually 3x or above—your brain will naturally filter this shadow out, and it will effectively disappear, allowing for a perfectly clear view of your target. This is why magnified optics and fixed front sights can coexist peacefully.
Gathering Your Tools and Components
Having the right gear before you start makes the process smooth and prevents damage to your equipment. Here’s what you’ll need:
- A Quality Optic: This can be a traditional rifle scope, a prism scope, or a low-power variable optic (LPVO).
- A Mounting System: You will need either a one-piece mount or a set of scope rings. Ensure they are the correct diameter for your scope tube (usually 1 inch or 30mm) and that they are designed for an AR-15’s flat-top Picatinny rail.
- Torque Wrench (in/lbs): This is non-negotiable. Overtightening screws can strip them or damage your scope, while under-tightening can lead to a loose optic. An inch-pound torque wrench provides the precision needed.
- Gun Vice or a Stable Rest: This holds your rifle securely, freeing up both your hands for the installation.
- Thread Locker: A medium-strength thread locker like blue Loctite is recommended to keep the mounting screws from vibrating loose.
- Bubble Level (optional but helpful): Useful for ensuring your scope is not canted.
The Step-by-Step Mounting Process
Now, let’s get your scope mounted. Follow these steps carefully for a secure and reliable installation.
Step 1: Prepare the Rifle and Mount
Secure your AR-15 in the gun vice, ensuring it’s stable. Make sure the rifle is unloaded. Attach the base of your one-piece mount or the lower rings to the Picatinny rail on the upper receiver. Hand-tighten the nuts to hold it in place for now.
Step 2: Set the Proper Eye Relief
This is a critical step for comfort and safety. Place the scope into the mount (without tightening the top rings yet). Shoulder the rifle naturally with your eyes closed. When you open your eyes, you should see a full, clear picture without any black shadowing around the edges—this is a full sight picture. Slide the scope forward or backward in the rings until you achieve this. The front sight will be visible at this point, but don’t worry about it.
Step 3: Level the Scope and Secure the Rings
While maintaining the correct eye relief, ensure the scope’s reticle is level. You can use a bubble level on a flat part of the scope turret for assistance. Once everything is aligned, begin tightening the ring screws. Follow a crisscross pattern, tightening each screw a little at a time. This ensures even pressure and prevents misaligning the scope tube. Refer to your mount’s manual for the specific torque value, but it typically ranges from 15 to 25 in/lbs.
Step 4: Finalize the Mount to the Rail
Now, secure the entire mount assembly to the rifle’s rail. Apply a small drop of blue Loctite to the mounting nuts or screws. Again, using your torque wrench and following the manufacturer’s specification (often 45-65 in/lbs), tighten the fasteners in a cross pattern.
Zeroing Your Scope with the Front Sight in Place
With the scope physically mounted, it’s time to zero it. Head to the range with your target set at a desired distance, such as 50 or 100 yards. The process is the same as with any other rifle. Fire a group of shots, then use the turrets on your scope to adjust the point of impact to match your point of aim. Through the magnified scope, you will likely not even notice the faint shadow of the front sight, and it will not interfere with achieving an accurate zero.
Considering Your Long-Term Setup
While the “see-through” method works perfectly well, some shooters prefer a completely unobstructed view. If you find the shadow bothersome at your preferred lower magnification settings, you have a couple of options. You can invest in a quick-detach (QD) mount and pair it with a flip-up front sight, giving you the flexibility to remove the optic or fold down the sight as needed. Alternatively, you can have a gunsmith replace the fixed front sight base with a low-profile gas block, creating a truly free-floating rail. However, for most applications, learning to look past the front sight is the simplest and most robust solution.
Mounting a scope on your AR-15 with a fixed front sight is a straightforward task that greatly enhances the rifle’s capability. By using the right tools, taking your time with eye relief and leveling, and understanding the optics at play, you can successfully integrate a modern scope with the classic silhouette of your rifle. Remember to always use a torque wrench for a secure hold, and don’t be concerned by the faint shadow of the front sight—it’s just a reminder of your rifle’s built-in redundancy.