First Impressions of CMMG Mk4 6mm ARC Resolute Upper Group Receiver
The CMMG Mk4 6mm ARC Resolute Upper Group Receiver promises to bring the long-range accuracy and ballistic advantages of the 6mm ARC cartridge to the widely adaptable AR-15 platform. CMMG is a well-respected name in the AR world, and the Resolute series suggests a commitment to quality and performance. I was eager to see if this upper group lives up to the hype, especially given the growing popularity of the 6mm ARC for both hunting and precision shooting.
I was seeking an upper that could provide flatter trajectories and better wind resistance than my standard 5.56 NATO AR-15, especially for engaging targets at distances beyond 300 yards. The 6mm ARC seemed like the perfect solution, offering a significant ballistic upgrade without requiring a complete rifle overhaul. The CMMG name and reputation for quality AR components sealed the deal.
Unboxing the CMMG Mk4 6mm ARC Resolute Upper Group Receiver, the first thing that struck me was its solid feel. The finish was clean and even, and the M-LOK handguard felt robust and well-attached. The weight was noticeable, but not excessive, suggesting a good balance between durability and maneuverability.
I considered upper groups from other manufacturers, specifically those from Aero Precision and Ballistic Advantage. Ultimately, I chose the CMMG because of their reputation for reliability and their commitment to using quality components throughout their build. I was also drawn to the Resolute series’ focus on precision.
My initial impression was one of cautious optimism. The build quality appeared excellent, and the specifications seemed promising, but the real test would be on the range. I was excited to see if the CMMG Mk4 6mm ARC Resolute Upper Group Receiver could deliver on its promises of long-range accuracy and enhanced ballistic performance.
Real-World Testing: Putting CMMG Mk4 6mm ARC Resolute Upper Group Receiver to the Test
First Use Experience
My first outing with the CMMG Mk4 6mm ARC Resolute Upper Group Receiver was at my local shooting range, which offers distances out to 600 yards. I mounted the upper on my existing AR-15 lower, slapped in a magazine loaded with Hornady 6mm ARC ammunition, and got to work zeroing my optic. The initial shots were promising, with tight groupings at 100 yards.
The weather was clear and mild, around 65 degrees Fahrenheit, with a slight breeze. I tested the upper with a variety of ammunition, including Hornady ELD Match and Federal Gold Medal Berger. The upper cycled flawlessly with all the tested ammunition.
The CMMG Mk4 6mm ARC Resolute Upper Group Receiver was incredibly easy to use. After a quick zeroing, I was consistently hitting steel targets out to 400 yards. The recoil was minimal, even less than my 5.56 AR, making it easy to stay on target for follow-up shots.
The only initial surprise was how much more effective the 6mm ARC was at longer ranges. The wind drift was noticeably less than my 5.56, and the impacts on steel were much more authoritative.
Extended Use & Reliability
After several months of use, the CMMG Mk4 6mm ARC Resolute Upper Group Receiver has proven to be incredibly reliable. I’ve put several hundred rounds through it in various conditions, from sunny days at the range to rainy afternoons on a hunting trip. It hasn’t experienced a single malfunction.
The finish is holding up well, with only minor wear marks on the brass deflector. The M-LOK handguard remains solid, and all components are still tight and secure.
Cleaning the CMMG Mk4 6mm ARC Resolute Upper Group Receiver is straightforward. The bolt carrier group is easy to disassemble and clean, and the barrel wipes down easily. Regular lubrication keeps everything running smoothly.
Compared to my previous experiences with other AR uppers, the CMMG clearly outperforms them in terms of accuracy and reliability. The 6mm ARC cartridge itself is a game-changer, and the CMMG upper allows me to fully realize its potential. It’s a significant step up in performance.
Breaking Down the Features of CMMG Mk4 6mm ARC Resolute Upper Group Receiver
Specifications
The CMMG Mk4 6mm ARC Resolute Upper Group Receiver boasts several key specifications that contribute to its performance. It is chambered in 6mm ARC and features a 16.1-inch medium tapered barrel. The 1-7.5 twist rate is ideal for stabilizing the heavier 6mm ARC projectiles.
It has an overall length of 16.5 inches and weighs in at 3.9 lbs. The upper receiver and handguard are constructed from 7075 T6 aluminum, ensuring both strength and light weight. It also includes a pistol-length gas system for reliable cycling.
The inclusion of a CMMG Zeroed Muzzle Brake effectively reduces recoil and muzzle rise, aiding in faster follow-up shots. The .750-inch gas block journal size is a standard dimension, allowing for easy replacement if needed. Finally, the M-LOK handguard provides ample space for mounting accessories.
These specifications are important because they contribute to the overall accuracy, reliability, and usability of the upper. The 6mm ARC caliber provides superior ballistics, while the quality construction ensures long-term durability. The M-LOK rail system allows for customization.
Performance & Functionality
The CMMG Mk4 6mm ARC Resolute Upper Group Receiver excels in its primary job: delivering accurate and reliable shots at extended ranges. The 6mm ARC cartridge, combined with the quality barrel and muzzle brake, makes this upper a joy to shoot.
Its strengths lie in its accuracy, minimal recoil, and reliable cycling. The weaknesses are few, but the pistol-length gas system might be less forgiving with certain ammunition types compared to a mid-length system.
The CMMG Mk4 6mm ARC Resolute Upper Group Receiver absolutely meets and even exceeds my expectations. It has transformed my AR-15 into a capable long-range platform.
Design & Ergonomics
The build quality of the CMMG Mk4 6mm ARC Resolute Upper Group Receiver is excellent. The 7075 T6 aluminum construction feels solid and durable. The weight is well-balanced, making it comfortable to shoot for extended periods.
The design is user-friendly, with an M-LOK handguard that provides plenty of space for mounting optics, lights, and other accessories. There is virtually no learning curve if you are already familiar with the AR-15 platform.
Durability & Maintenance
The CMMG Mk4 6mm ARC Resolute Upper Group Receiver is built to last. The quality materials and robust construction suggest it will withstand years of use. With proper care and maintenance, it should provide reliable performance for a long time.
Maintaining the upper is simple. Regular cleaning and lubrication of the bolt carrier group and barrel are all that is needed to keep it in top condition.
Accessories and Customization Options
The CMMG Mk4 6mm ARC Resolute Upper Group Receiver does not come with any included accessories beyond the assembled upper receiver itself. However, the M-LOK handguard allows for a wide range of customization options.
The upper is compatible with any standard AR-15 lower receiver, magazines designed for the 6mm ARC cartridge, and a variety of optics, lights, and other accessories from popular brands like Magpul, Streamlight, and Vortex. Mounting a high-quality optic is crucial to realizing the full accuracy potential of this upper.
Pros and Cons of CMMG Mk4 6mm ARC Resolute Upper Group Receiver
Pros
- The CMMG Mk4 6mm ARC Resolute Upper Group Receiver delivers exceptional accuracy, especially at longer ranges, thanks to the 6mm ARC cartridge and quality barrel.
- The recoil is surprisingly mild, making it easy to stay on target and deliver quick follow-up shots.
- The reliability of the upper is outstanding, with consistent cycling and no malfunctions experienced during testing.
- The M-LOK handguard provides ample space for mounting various accessories, allowing for a highly customized setup.
- CMMG’s reputation for quality and durability provides peace of mind, knowing that this upper is built to last.
Cons
- The price point of the CMMG Mk4 6mm ARC Resolute Upper Group Receiver may be a barrier for some, as it represents a significant investment compared to entry-level uppers.
- A magazine is not included, requiring a separate purchase.
Who Should Buy CMMG Mk4 6mm ARC Resolute Upper Group Receiver?
The CMMG Mk4 6mm ARC Resolute Upper Group Receiver is perfect for hunters seeking a flat-shooting, accurate cartridge for medium to large game. It is also well-suited for competitive shooters looking for an edge at longer ranges, and any enthusiast who wants to upgrade their AR-15 to a more capable and versatile platform.
Those who should skip this product are individuals on a tight budget, or those who primarily shoot at very short ranges where the advantages of the 6mm ARC are less pronounced. Someone new to the AR-15 platform might also want to start with a simpler and less expensive option.
A must-have accessory for this upper is a high-quality optic with sufficient magnification for long-range shooting. A bipod or shooting rest is also recommended for maximizing accuracy.
Conclusion on CMMG Mk4 6mm ARC Resolute Upper Group Receiver
The CMMG Mk4 6mm ARC Resolute Upper Group Receiver is a high-quality, accurate, and reliable upper that brings the ballistic advantages of the 6mm ARC cartridge to the AR-15 platform. While the price may be a consideration for some, the performance and durability justify the investment.
The value proposition is strong, especially for those seeking a significant upgrade in accuracy and long-range capability. It’s a well-built upper that will deliver consistent results.
I would personally recommend the CMMG Mk4 6mm ARC Resolute Upper Group Receiver to anyone serious about long-range shooting or hunting. If you are ready to take your AR-15 to the next level, this upper is a solid choice. Go ahead and experience the difference that quality craftsmanship and superior ballistics can make!