• Reading time:23 mins read
  • Post category:Upper Receivers
  • Post last modified:September 21, 2023
  • Post published:December 8, 2022

Best 6mm ARC Upper Receiver Review

What is a 6mm ARC upper receiver? 😏

It is a key component of a firearm that operates with the 6mm ARC cartridge, a versatile and highly efficient round. This upper receiver is engineered to match the unique specifications of the 6mm ARC, ensuring optimal performance and accuracy. Part of the modular design of modern rifles, the upper receiver can be interchanged with other compatible firearm platforms, offering flexibility to the users.

Our Top Pick
Stag Arms 15 Covenant Left Hand 6mm ARC Upper Receiver
The upper receiver is constructed from Mil-Spec 7075-T6 aluminum and boasts a Type III Hardcoat Anodized finish for durability. Specifically designed to seamlessly pair with 6mm ARC cartridge barrels, it incorporates a Rifle Length gas system. The gas block journal measures .750 inches in diameter, and the barrel features a precise twist rate of 1:7.
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Advantages 😎

🟡 Firstly, one of the foremost benefits is its compatibility with a multitude of firearm platforms. ↪️ This uniquely versatile feature allows users to interchange the upper receiver with different rifles, thereby extending the scope of use and offering greater flexibility.

🟡 Secondly, the construction materials used in these receivers, particularly the high-quality, durable aluminium alloy 7075-T6, offer an excellent balance between strength and weight. ↪️ This unique combination makes handling the rifle easier, ensuring both comfort and longevity of use for the shooter.

🟡 Moreover, the inclusion of a Picatinny rail system enhances the utilitarian aspect of this upper receiver.↪️ It presents the shooter with the ability to attach various optics and accessories, optimizing the firearm’s performance across different tactical and recreational scenarios.

🟡 The presence of features such as the forward assist and the ejection port cover further improves the functional efficiency of the rifle. ↪️ While the forward assist aids in troubleshooting and chambering rounds, the ejection port cover protects the internals of the rifle from dirt and debris, safeguarding its performance and durability.

🟡 Finally, one distinctive advantage is the attention paid to detail in its design and finish. ↪️ From ensuring compatibility with the barrel nut and extension to providing a corrosion-resistant finish like anodizing or Cerakote, every element is meticulously addressed.

How To Choose 🧐

The upper receiver is a pivotal component of your rifle, housing critical parts like the bolt carrier group and barrel. Here’s what you should know:

  • Material: Choose an upper receiver made from high-quality, durable aluminium alloy like 7075-T6. It ensures both strength and a manageable weight.
  • Picatinny Rail: The top of your upper receiver features a Picatinny rail (often called “flattop” or “A3”) for attaching optics and accessories. Ensure it’s compatible with your chosen optics.
  • Forward Assist: Some upper receivers include a forward assist, which can be handy for troubleshooting or chambering rounds. While not essential, it’s a nice feature for some shooters.
  • Ejection Port Cover: This hinged cover on the side of the receiver keeps dirt and debris out of your rifle. Most upper receivers come with this feature, and it’s wise to keep it in place.
  • Compatibility: Verify that your upper receiver is designed for 6mm ARC cartridges, with the proper bolt face and barrel extension.
  • Barrel Nut and Extension: Ensure compatibility with the barrel nut and extension required for your 6mm ARC build. Proper alignment is crucial for accuracy and reliability.
  • Finish: Look for a corrosion-resistant finish like anodizing or Cerakote to protect your receiver from wear and tear.

When selecting an upper receiver for your 6mm ARC rifle, take into account your specific needs and preferences. Consulting with a knowledgeable gunsmith or experienced AR-15 builder can provide further guidance, ensuring your build meets your expectations.

Types 🤠

The first is the Direct Impingement (DI) Upper Receiver. The DI system is one of the most common designs. ✔️ It works by directing gases from the fired round back into the gun’s upper receiver, using this pressure to push the bolt carrier back and cycle the action. 🔴 While this design can lead to a hotter and dirtier action, it is lighter and has fewer moving parts, making it a popular choice for lightweight or budget builds.

The second is the Piston Upper Receiver. This system uses a piston to transfer gas energy, instead of pushing the gases back into the receiver. ✔️ The piston design keeps the action cleaner as it doesn’t direct fouling back into the receiver, which can be a significant benefit if maintenance is a concern. 🔴 However, piston uppers tend to be heavier and more expensive than their DI counterparts.

Both types have their strengths and weaknesses, and the choice between the two largely depends on the shooter’s preferences and intended use of the firearm.

Best 6mm ARC Upper Receiver Review

1# Stag Arms 15 Covenant Right Hand 6mm ARC Upper Receiver

Stag Arms 15 Covenant Right Hand 6mm ARC Upper Receiver

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The Stag Arms 15 Covenant Right Hand 6mm ARC Upper Receiver is a top-quality product that is perfect for anyone looking to upgrade their firearm. This upper receiver is made from Mil-Spec 7075-T6 aluminium, and it features a black Type III hard coat anodized finish. It is compatible with 6mm ARC cartridges, and it has a 20″ barrel length. The barrel is made from 416R stainless steel, and it has a 1-7 twist rate. The handguard on this upper receiver is 16.5″ long, and it is made from Picatinny material. It also has a Picatinny gun rail. The muzzle device on this upper receiver is the VG6 Gamma, and it weighs 4.5 oz.

Video review

  • Made from Mil-Spec 7075-T6 aluminium
  • Features a black Type III hard coat anodized finish
  • Compatible with 6mm ARC cartridges
  • Has a 20″ barrel length
  • The barrel is made from 416R stainless steel
  • 1-7 twist rate
  • The handguard is 16.5″ long and made from Picatinny material
  • Picatinny gun rail included
  • The upper receiver is not ambidextrous
  • The charging handle is also not ambidextrous


2# Stag Arms 15 Covenant Left Hand 6mm ARC Upper Receiver

Stag Arms 15 Covenant Left Hand 6mm ARC Upper Receiver

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For those shoppers seeking unparalleled performance and dependability, the Stag Arms 15 Covenant Left Hand 6mm ARC Upper Receiver is the product for you. This upper receiver is made from Mil-Spec 7075-T6 aluminium and features a Type III Hardcoat Anodized finish. It is designed to work with 6mm ARC cartridge barrels and has a Rifle Length gas system. The gas block journal size is .750 in and the barrel twist rate is 1-7. The handguard length is 16.5 in and the muzzle device is a VG6 Gamma. This upper receiver weighs 4.5 oz and comes with a 416R Stainless Steel barrel.

Video review

  • 6mm ARC Upper Receiver
  • Made from Mil-Spec 7075-T6 aluminium
  • Features a Type III Hardcoat Anodized finish
  • Designed to work with 6mm ARC cartridge barrels
  • Rifle Length gas system
  • The gas block journal size is .750 in
  • The barrel twist rate is 1-7
  • The handguard length is 16.5 in
  • The muzzle device is a VG6 Gamma
  • The bolt carrier group is proprietary and must be purchased from Stag Arms
  • No dust cover or forward assist


3# CMMG Mk4 Resolute Upper Receiver

CMMG Mk4 Resolute Upper Receiver

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If you’re looking to top off your next AR15 build, the CMMG Mk4 Resolute Upper Receiver Group is a perfect choice. This upper receiver group is ready to pair with any AR15 lower receiver and features a billet 6061 T6 aluminium construction with an Armor Black finish. It’s equipped with a CMMG Zeroed Muzzle Brake for superior muzzle control and comes with an M-LOK rail for attaching your favourite accessories. With its .750″ gas block journal diameter, this upper receiver group is perfect for any application.

  • Billet 6061 T6 aluminium construction
  • Armour Black finish
  • CMMG Zeroed Muzzle Brake
  • M-LOK rail for accessories
  • .750″ gas block journal diameter
  • No forward assist
  • Cannot be used with a standard charging handle
  • No dust cover


4# CMMG Mk4 6mm ARC Resolute Upper Group

CMMG Mk4 6mm ARC Resolute Upper Group

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The CMMG Mk4 6mm ARC Resolute Upper Group is the perfect choice for any serious shooter looking to harness the power of the 6mm ARC cartridge. This RESOLUTE upper group is designed to pair with any standard AR15-pattern lower group, and features a uniquely designed 16.1″ barrel for outstanding performance. The barrel is made from 7075 T6 aluminium for maximum durability, and is equipped with a medium tapered profile and 1-10″ twist rate for exceptional accuracy. The gas system is pistol-length for reliability, and the gas block journal size is .750″. The M-LOK attachment/mount system provides easy mounting of accessories, and the muzzle brake keeps your shots on target.

  • Outstanding performance
  • Durable construction
  • Easy mounting of accessories
  • Keeps shots on target
  • May be too powerful for some shooters
  • Muzzle brakes can be noisy and distracting


5# Brenton USA Scout 18in 6mm ARC Upper Receiver

Brenton USA Scout 18in 6mm ARC Upper Receiver

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The Brenton USA Scout 18in 6mm ARC Upper Receiver is a high-quality receiver made from 7075-T6 aircraft-grade aluminium. It features Brenton’s patent-pending RecevierLock control system for a tight, secure fit. The handguard is made from Brenton RealFeel, PolyCore material for a natural feel and the charging handle is gas-diverting. The BCG is 8620 carrier w/ 9310 bolt w/ NiB protective coating. The rifle is covered by Brenton’s Forever Warranty against defects in materials and workmanship and has a sub-MOA Guarantee.

  • It is made from 7075-T6 aircraft-grade aluminium.
  • Features Brenton’s patent-pending RecevierLock control system for a tight, secure fit.
  • The handguard is made from Brenton RealFeel, PolyCore material for a natural feel.
  • The charging handle is gas-diverting.
  • BCG is 8620 carrier w/ 9310 bolt w/ NiB protective coating.
  • The rifle is covered by Brenton’s Forever Warranty against defects in materials and workmanship and has a sub-MOA Guarantee
  • Limited availability of parts and accessories
  • Somewhat difficult to assemble


6# Brenton USA Tracker 22in 6mm ARC Upper Receiver

Brenton USA Tracker 22in 6mm ARC Upper Receiver

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The Brenton USA Tracker 22in 6mm ARC Upper Receiver is a good choice for your next hunting rifle. With its Brenton Patent Pending RecevierLock, HuntSpec controls and tolerance, and RealFeel handguard, this upper receiver is sure to provide a great shooting experience. The gas-diverting charge handle and 8620 carriers with 9310 bolts make this a great choice for those who want a durable and reliable hunting rifle. And with Brenton’s Life-Time Warranty and sub-MOA Guarantee, you can be confident in your purchase.

  • HuntSpec controls and tolerance
  • RealFeel handguard
  • Gas-diverting charge handle
  • 8620 carriers with 9310 bolts
  • Durable and reliable
  • Life-Time Warranty
  • Sub MOA Guarantee
  • The weight is a bit too much for some people


Installation 🛠️

Before beginning, it’s important to gather all the necessary tools. Here’s what you’ll need:

  • Upper Vise Block: This tool holds the upper receiver securely in place during the installation process.
  • Armorer’s Wrench: This multi-purpose tool is used for numerous steps throughout the installation process.
  • Torque Wrench: Critical for applying the correct amount of tension during the barrel nut installation.
  • Roll Pin Punches and Hammer: These are used to install roll pins.
  • Grease: This reduces friction and ensures the smooth operation of components.

🔰 Firstly, you need to secure the upper receiver in an upper vice block. This is a crucial step to ensure that the receiver stays stationary and safe throughout the installation process.

🔰 Secondly, you will need to apply a bit of grease to the barrel extension and inside the receiver. This step is essential for reducing friction and ensuring a smooth operation of components. Once the grease is applied, you can proceed to insert the barrel into the front of the receiver.

🔰 Next, you will slide the barrel nut over the barrel and screw it onto the receiver. The armourer’s wrench comes into play here to tighten the nut. Moreover, a torque wrench should be utilized to apply the manufacturer’s recommended amount of torque.

🔰 Following that, it’s time to install the gas block and gas tube. The gas block is secured to the barrel through set screws or roll pins, whereas the gas tube is typically pinned into the gas block.

🔰 Subsequently, you will install the handguard. This process can vary greatly depending on the design of the handguard, so be sure to refer to the manufacturer’s instructions.

🔰 Finally, you wrap up the installation process by installing the bolt carrier group and charging handle. These parts slide into the back end of the upper receiver. Remember, always refer to the manufacturer’s instructions for any specific requirements or notes.

The installation of a 6mm ARC upper requires a systematic approach and the right tools, but with patience and diligence, it is a task that can be accomplished successfully.


Are there any specific maintenance or cleaning requirements for a 6mm ARC upper receiver?

Maintenance and cleaning are crucial to ensure optimal performance and longevity. Here’s a detailed breakdown of the recommended procedures:

⚪ First, Unload the Firearm: Before performing any maintenance, ensure the firearm is unloaded. Remove the magazine, clear the chamber, and visually inspect it to confirm it’s safe.

⚪ Secondly, Field Strip the Upper Receiver: To do this disassemble the upper receiver from the lower receiver following the manufacturer’s instructions. This typically involves pushing out the takedown pins and separating the upper and lower halves.

⚪ Moreover, Inspect for Wear and Damage: It is recommended to examine all components, including the bolt carrier group, barrel, and gas system, for signs of wear, damage, or fouling. From our experience – pay particular attention to the bolt face, firing pin, and extractor for carbon buildup or debris.

⚪ Furthermore, Cleaning the Barrel: Clean the barrel bore using a cleaning rod, bore brush, and solvent. In order to do this step  – run the bore brush back and forth several times to remove fouling and residue. Then, patch the barrel with solvent-soaked patches until they come out clean. Finally, apply a light coat of gun oil to prevent corrosion.

⚪ Next, Bolt Carrier Group: Disassemble the bolt carrier group. It can be done by removing the firing pin, extractor, and extractor spring. After that clean these components thoroughly with solvent and a brush, then wipe them clean. And apply a thin layer of lubricant to these parts before reassembly.

⚪ Additionally, Gas System Maintenance: If your 6mm ARC upper has an adjustable gas block, check and adjust it if needed according to the manufacturer’s guidelines. Ensure that the gas tube and gas ports in the barrel are free from obstructions. Use a pipe cleaner or brush to clean them.

⚪ Finally, Reassembly and Lubrication: Reassemble the upper receiver, ensuring all components are properly seated and secured. Apply a light coat of high-quality gun oil or lubricant to friction points, such as the bolt carrier group and charging handle. Do not over-lubricate, as excess oil can attract dirt and debris.

 Always refer to the manufacturer’s recommendations for specific maintenance intervals and guidelines.

Are there any known issues or common malfunctions associated with the 6mm ARC upper receivers?

Yes, there are a few known issues or common malfunctions associated with the 6mm upper receivers. These include:

  • 🔴 Overheating: The 6mm ARC cartridge can generate a lot of heat, especially when fired rapidly. This can lead to overheating of the upper receiver, which can cause malfunctions such as chambering issues, extraction problems, and cook-offs.
  • 🔴 Bolt carrier group (BCG) wear: The 6mm ARC cartridge has a higher chamber pressure than other popular AR-15 cartridges, such as the 5.56 NATO and .300 Blackout. This can lead to increased wear on the BCG, particularly the extractor and ejector.
  • 🔴 Magazine compatibility: Not all AR-15 magazines are compatible with the 6mm ARC cartridge. Some magazines may need to be modified or replaced in order to feed reliably.

It is important to note that these issues are not unique to this upper receiver. They can also occur with other AR-15 upper receivers that are chambered for high-pressure cartridges, such as the 6.5 Grendel and .308 Winchester.

Can I use 5.56 or .223 ammunition with a 6mm ARC upper receiver?
🛑 No, you cannot use 5.56 or .223 ammunition with this upper receiver. The 6mm ARC was meticulously designed with specific dimensions and ballistics that are distinct from those of the 5.56 and .223 rounds.

⚠️ It is crucial to understand that the 6mm ARC offers superior performance and optimized characteristics tailored for its chambering. Attempting to use incorrect ammunition not only jeopardizes the functionality and integrity of your firearm but also poses a significant risk of injury to the user.

Therefore, it is of utmost importance to adhere to the manufacturer’s specifications and always employ the appropriate ammunition designated for your firearm. By doing so, you ensure both the longevity of your firearm and your personal safety.

Can I use hand-loaded ammunition with a 6mm ARC upper receiver??
✅ Yes, you can use hand-loaded ammunition with this upper receiver, but it’s important to do so with caution. Handloading offers the opportunity to customize your rounds, tailoring them to your specific needs and potentially improving accuracy and performance.

❌ However, it is crucial to exercise precision and adhere to proper handloading practices to ensure safety and prevent any damage to your rifle. Always double-check that the hand-loaded rounds meet the correct dimensions for your 6mm ARC upper receiver, as using ammunition that is ill-fitted can lead to malfunction or even accidents.

Moreover, it’s worth noting that certain firearms manufacturers may consider the use of hand-loaded ammunition as voiding the warranty. To avoid any complications, it is advisable to consult the manufacturer beforehand to understand their policies and guidelines.

Is a 6mm ARC upper compatible with standard AR-15 lowers?

🟢 Yes, a 6mm ARC upper receiver will work with a standard AR-15 lower receiver. The upper and lower receivers are interchangeable between AR-15 variants regardless of calibre.

The caveat is that the 6mm ARC upper must be used with 6mm ARC-specific magazines. It will not function properly with standard 5.56 NATO magazines. This is because the 6mm ARC round is slightly longer than 5.56 NATO.

❌ However, since the magazine well and magazine catch are part of the lower receiver, a standard AR-15 lower will interface properly with 6mm ARC magazines.

The lower receiver houses the trigger group, buffer system, grip, stock, and controls. These are not impacted by the change in calibre and will work reliably with a 6mm ARC upper.

🔴 The only consideration is that an adjustable gas block may be desirable to fine-tune operation when pairing a 6mm ARC upper with a lower. But even a standard mil-spec lower will be fully compatible with a dedicated 6mm ARC upper receiver.

Conclusion 🤩

The 6mm ARC upper receiver offers a unique blend of compatibility, performance, and durability. It capitalizes on the efficient 6mm ARC cartridge and incorporates design elements that cater to both professional and recreational shooters.  From the material used to the inclusion of features like the Picatinny rail, forward assist, and ejection port cover, every detail contributes to its enhanced functionality.

Thus, when choosing an upper receiver for your rifle, it’s essential to carefully consider your specific needs and preferences, ensuring that your build not only meets but surpasses your expectations. Remember, the right selection will significantly affect your firearm’s performance, reliability, and longevity.

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23 hours ago

I’m completely new to semi-auto rifle builds, so I’ve got a few basic questions. To clarify, when I say “new,” I mean I have very little experience in this area. I do own some semi-auto .22LR rifles and shotguns, but I haven’t ventured into the world of semi-auto rifles much.
I’m not in a hurry, but I’ve been contemplating a new build or purchase. While I have a good collection of precision bolt rifles, I haven’t really dabbled in semi-automatic rifles before. I’m considering the 6mm ARC chambering for this project. My goals are to create a highly accurate platform for plinking out to 1,000 yards, but I also want it to be practical for hunting deer and coyotes. I plan to reload for this rifle, and I’d prefer something on the lighter side for ease of carrying during hunting trips.

    23 hours ago
    Reply to  Freepilot

    If you’re new to ARs, I would suggest buying one for your first experience. Building them can be a bit challenging, and many newcomers may not be sure about their preferences yet.

      23 hours ago
      Reply to  Freepilot

      For a 6MM ARC build, I’d prefer assembling it myself since I have all the necessary tools. I’d prioritize quality upper and lower receivers with a tight fit, along with a thermally fitted upper. A high-quality 2-stage trigger, such as the Schmid Tool, is essential. I’d invest in the best barrel I can afford because precision matters with this round. ARs can achieve extremely tight groupings, and spending a bit more on a superior barrel is worth it, considering the potential cost of trying to make a lower-quality barrel meet your accuracy expectations with ammunition.

        23 hours ago

        Hey folks, I’ve been having some issues with my 6mm ARC upper. It’s not feeding rounds smoothly from the magazine. Anyone else experienced this? Any ideas for troubleshooting?

          23 hours ago
          Reply to  David

          I had a similar problem with mine. First, make sure you’re using compatible magazines for 6mm ARC. If that’s not the issue, check the feed ramps on your upper and lower. Sometimes a bit of polishing can help.

            Yan Wei
            Yan Wei
            23 hours ago

            Hello! Can I convert my existing AR-15 to 6mm ARC with an upper receiver swap?

              23 hours ago

              I’m a big fan of Brenton upper receivers. They make a high-quality product at a reasonable price. I have one and it’s been great.

                23 hours ago

                 I’m thinking about building a 6mm ARC upper receiver for hunting. What barrel length do you recommend?

                  23 hours ago
                  Reply to  Nushi

                  I recommend a 20- or 22-inch barrel for hunting. This will give you the velocity and energy you need to take down large game at long distances.