Understanding the AR9 Upper Receiver
Barrel
The barrel is arguably the most important part of the upper receiver. The length and the rifling twist rate of your barrel directly impact accuracy and the effective range of your AR9. The appropriate twist rate is critical to stabilizing 9mm bullets. Common barrel lengths vary, with shorter barrels favored for pistol configurations and longer barrels often preferred for more extended ranges. The material of the barrel (stainless steel, chrome moly steel) influences its durability and corrosion resistance. Understanding the intended use of your AR9 will dictate your barrel choice.
Bolt Carrier Group (BCG)
The bolt carrier group (BCG) is essential for the AR9’s blowback operation. Unlike an AR15 which uses a gas system to cycle, AR9s utilize a straight blowback mechanism. The BCG is specifically designed for the 9mm cartridge and includes a bolt face designed for the 9mm rim. Selecting a high-quality BCG ensures reliable extraction, ejection, and cycling. Ensure your BCG is compatible with your upper receiver, and that it is properly heat treated.
Charging Handle
The charging handle allows you to manually cycle the action, chambering a round or clearing a malfunction. While most charging handles are compatible, look for an extended or ambidextrous charging handle to enhance ease of use, especially under stress. The charging handle’s design is important.
Handguard
The handguard is the part you grip, allowing you to handle the rifle safely and comfortably. It also protects the barrel and provides attachment points for accessories such as sights, lights, and grips. The handguard’s features play an important role. M-LOK and KeyMod are popular mounting systems. The length of your handguard influences the overall appearance of your AR9 and allows for proper space to mount accessories.
Upper Receiver
The upper receiver itself, the foundation on which everything is built, is generally made of aluminum. Ensure the upper receiver’s construction is robust enough to handle the pressures of firing 9mm rounds. It also might include features such as a dust cover, which protects the internals from debris, and a forward assist, a mechanical device to help seat a round if the bolt doesn’t fully close.
Muzzle Device
The muzzle device directs the gases from the fired round. Options include muzzle brakes, compensators, or suppressors. These devices reduce recoil, manage muzzle rise, and can significantly enhance the overall shooting experience. Selecting the right muzzle device depends on your goals.
Material Considerations
High-quality materials are key to a reliable AR9. The upper receiver itself is typically made from aluminum alloys, known for their strength and relatively light weight. A hard-anodized finish provides further protection against wear and corrosion. The barrel is typically made of stainless steel or chrome moly steel, each offering different advantages in terms of durability and accuracy. The BCG should be made of durable materials such as steel with a proper heat treatment. Investing in quality materials early on will save you headaches later.
Aftermarket Options
The AR9 platform is highly customizable. Aftermarket upgrades can enhance performance and aesthetics. Consider free-float handguards for improved accuracy, enhanced charging handles for easier manipulation, and improved triggers for crisper breaks. These upgrades allow you to tailor your AR9 to your specific needs and preferences. Don’t be afraid to make your AR9 feel like your own with aftermarket parts.
Exploring the AR9 Lower Receiver
Lower Receiver
The lower receiver is the part of your AR9 that houses the fire control group, magazine well, and buffer system. It’s the legal “firearm” component and the foundation for your AR9 build. Choosing the right lower receiver is critical.
Fire Control Group (FCG)
The fire control group (FCG) includes the trigger, hammer, and disconnector. The trigger determines how the firearm fires. Trigger types include single-stage and two-stage. The trigger pull weight is another crucial factor affecting accuracy. A lighter, crisper trigger can improve accuracy.
Safety Selector
The safety selector allows the shooter to control whether the firearm can fire. The safety selector is an essential safety feature. Make sure the safety selector functions smoothly and reliably.
Buffer Tube Assembly
The buffer tube assembly is essential for the 9mm blowback operation of the AR9. It consists of the buffer tube, buffer, and spring. The weight of the buffer and the spring’s resistance play a critical role in controlling the bolt’s movement during the firing cycle. Use the correct buffer weight and spring designed for 9mm to ensure reliable cycling. This is key to functionality.
Magazine Release
The magazine release is the mechanism that allows you to release the magazine. The magazine release should be easily accessible. Choose a magazine release compatible with your chosen magazine type.
Pistol Grip
The pistol grip is for comfort and ergonomics. Ergonomic pistol grips can enhance your grip and control. Choose a grip that fits your hand size and shooting style.
Stock or Brace
The stock or brace affects the classification of the AR9. A stock (or shoulder stock) means it’s an SBR (Short Barreled Rifle) under NFA regulations. A pistol brace allows it to be configured as a pistol. The choice of a stock or pistol brace is a personal decision.
9mm Magazine Compatibility
The AR9 uses a variety of magazine types, depending on the lower receiver design. The most common are Glock-style, Colt-style, and those designed to work with certain brands. Make sure your lower receiver is compatible with the magazine you intend to use. The AR9 must feed reliably, so this is important. Magazine adaptors may be needed for some configurations.
Considerations Regarding Lower Receiver Finishes and Materials
High-quality materials are essential for the lower receiver. Aluminum alloys are standard for their strength and weight. Finishes such as hard-coat anodizing provide protection against wear and corrosion.
Compatibility and Considerations
Ensuring Proper Compatibility
One of the most critical aspects of building an AR9 is ensuring that all components work together. Here are several things to think about. Check that your upper and lower receiver mate correctly and fit together without excessive play. Bolt carrier group compatibility is critical. The BCG must be designed for 9mm. Magazine compatibility is also a key factor, as the lower receiver must accept the magazines you intend to use. Make sure everything fits.
Buffer System Selection
The buffer system, including the buffer weight and spring, is crucial for a reliable AR9. The weight of the buffer must match the energy of the 9mm cartridge. Incorrect buffer weights and springs lead to malfunctions, like failure to eject or failure to feed.
Understanding the Blowback System
The AR9 uses a blowback system. The BCG is driven by the energy of the fired cartridge, unlike the gas-operated system in an AR15. The mass of the BCG and the spring rate of the buffer spring are vital for proper operation.
Legal Considerations
The AR9 platform has its own set of legal considerations. Building an AR9 pistol is legal. If the AR9 is equipped with a stock and has a barrel under a certain length, it’s considered an SBR (Short Barreled Rifle), and may be subject to NFA regulations. Make sure you understand the local and federal laws. It is your responsibility.
Building Your AR9
If you are new to the AR9 platform, here are some tips. Make sure you have the correct tools. A good set of tools is essential for assembling your AR9. Follow the instructions carefully, and always be aware of safety. Do not skip steps.
Troubleshooting Common Issues
Malfunctions can happen with any firearm. If you experience a failure to feed, check the magazine, the feed ramps, and the bolt’s movement. If your AR9 has a failure to eject, check the extractor, ejector, and the case. Light primer strikes can be caused by a weak hammer spring or a dirty firing pin. Bolt carrier sticking can be caused by over lubrication or other issues.
Maintenance and Care
Proper maintenance is crucial to extend the life of your AR9. Regularly clean the upper and lower receivers. Use appropriate lubricants for smooth operation. Store the AR9 in a cool, dry place.
Conclusion
Building an AR9 is a rewarding experience that allows you to customize a firearm to your specific needs. This guide has covered the essential components of the upper and lower receivers, along with important considerations for compatibility, assembly, and maintenance. Your journey into the AR9 world has just begun. Remember to always prioritize safety. If you are still unsure, there are many reliable resources.
