AR-10 80% Lower: The Ultimate Guide for Builders

Understanding the Foundation: What is an AR-10 80% Lower?

The allure of the AR-10 platform is undeniable. It represents a leap in power and range compared to its smaller cousin, the AR-15. The modular design of this rifle opens doors to endless customization, offering shooters the ability to tailor their firearm to their precise needs and preferences. For those seeking a deeper connection with their weaponry and a unique level of control, building an AR-10 from an AR-10 80% lower is a rewarding pursuit. This article serves as your comprehensive guide, providing the information, insights, and tips needed to navigate the world of AR-10 80% lowers and successfully complete your build.

For many, the AR-10 represents a symbol of American ingenuity, a tool capable of everything from hunting large game to long-range target shooting. Building your own AR-10 allows you to explore the full potential of this platform, customizing every aspect of your firearm from the barrel to the stock. This journey allows a deeper understanding of the mechanics of the AR-10, something you simply can’t get from purchasing a pre-built rifle. This guide will equip you with the knowledge to create a personalized and high-performing AR-10.

At the heart of any AR-10 rifle lies the lower receiver. This crucial component houses the fire control group, the magazine well, and the buffer tube assembly. An AR-10 80% lower is a partially completed lower receiver. It’s typically made from billet aluminum, though steel variants are also available. The “80%” designation refers to the stage of completion. It means the lower is missing a significant portion of the machining required to make it a fully functional firearm. Specific areas, such as the fire control group pocket, trigger and hammer pin holes, and the buffer tube threads, remain unmachined, leaving the builder to complete these steps.

The intention of this design is to offer builders control over the process. This offers a more hands-on building experience, and more importantly, circumvents the federal requirement for the lower to be considered a “firearm”. This also means the AR-10 80% lower can be purchased without the need for an FFL transfer, which streamlines the process. When you purchase the lower, it is essentially a paperweight until you perform the necessary machining.

The choice of material for the AR-10 80% lower influences its durability, weight, and price. Aluminum is the most common choice due to its balance of strength, weight, and cost-effectiveness. It offers a good foundation for a rugged firearm. Steel lowers, though heavier, can be more durable. Consider your intended use and budget when deciding on the material. There are also polymer lowers available, though not as common as their aluminum counterparts, they are usually lighter and less expensive.

Navigating the Legal Landscape

The legal status of AR-10 80% lowers is complex and varies by jurisdiction. Understanding the relevant regulations is crucial before beginning your build. In general, AR-10 80% lowers are not considered firearms under federal law. This is because they haven’t been completed. However, each state and sometimes even local municipalities have their own laws regarding the manufacturing and possession of these components.

It is your responsibility as the builder to research and comply with all applicable federal, state, and local laws. Some states may require serialization or registration of completed 80% lowers. Others may have restrictions on the types of firearms that can be built. Some states may require the builder to place a serial number on the item. Always keep yourself informed of changing regulations. It is important to stay up-to-date. There may be new laws passed at the federal, state, or local level. Be sure to check the laws periodically.

It’s also important to be aware of the legal implications of transferring a completed AR-10 80% lower to someone else. In some jurisdictions, this may be considered manufacturing and distribution of a firearm, which could be subject to federal licensing requirements. Before undertaking any build, consult with a legal professional, especially if you have any doubts about the legal aspects of your project. This may also be the case if you plan to sell any 80% lowers.

Essential Tools and Equipment for the Build

Completing an AR-10 80% lower requires a specific set of tools and equipment. The investment upfront may seem daunting, but the cost can be offset by the satisfaction of doing the work yourself and the cost savings compared to purchasing a complete lower.

• Milling Machine or Drill Press: This is the workhorse of the project. A milling machine offers the most precise control for machining the fire control group pocket and other features. A drill press can be used, though it may require more care and precision to achieve the desired results.
• Jigs and Fixtures: A quality jig specifically designed for AR-10 80% lowers is essential. It holds the lower securely during machining, ensuring proper alignment and making the process much simpler. Jigs also help make the process safer.
• End Mills and Drill Bits: These are the cutting tools used to remove material. You will need a set of end mills for creating the fire control group pocket, and drill bits of various sizes for drilling the pin holes. The proper sizes are typically specified in the included instructions, or are easily found online. Be sure to purchase quality cutting tools for best results.
• Tools for Assembly: These include punches for installing pins, a hammer, and possibly a vise for holding parts during assembly.
• Safety Equipment: Eye protection (safety glasses or goggles) is mandatory. Ear protection (earplugs or earmuffs) is also essential, especially when using a drill press or milling machine. Gloves are also a good idea to protect your hands.

If you’re new to machining, a drill press and a good jig can be a good starting point. Start with a comprehensive set of instructions. A mill is preferred.

The Machining Process: A Step-by-Step Guide

The process of finishing an AR-10 80% lower involves a series of carefully executed steps. Patience, precision, and following instructions are key. Always consult the manufacturer’s instructions for your specific AR-10 80% lower, as the exact procedures may vary.

1. Preparation: Securely clamp the AR-10 80% lower into the jig according to the manufacturer’s instructions. Ensure the lower is level and properly aligned. Review the instructions and familiarize yourself with the steps. Double-check your setup before starting any machining.
2. Milling the Fire Control Group Pocket: Using the appropriate end mill, carefully mill out the fire control group pocket. This is where the trigger, hammer, disconnector, and related components will be housed. Take slow, controlled passes, removing small amounts of material at a time.
3. Drilling the Pin Holes: Drill the holes for the trigger, hammer, and selector switch. Use the correct drill bit sizes specified in the instructions. Be meticulous in your alignment.
4. Creating the Buffer Tube Threads: Using the appropriate tap, thread the buffer tube housing. Use cutting oil to lubricate the threads.
5. Deburring and Finishing: Once all machining is complete, carefully deburr all edges and remove any sharp points. Sanding, polishing, or applying a protective finish (such as Cerakote or anodizing) can improve the appearance and durability of the lower.

Assembling Your AR-10 Lower

Once the machining is complete and the lower has been properly finished, it’s time to assemble the lower parts kit (LPK). This involves installing the various small components that make the lower functional.

1. Installing the Fire Control Group: Install the trigger, hammer, disconnector, and springs into the receiver. Use the appropriate pins to secure these components.
2. Installing the Bolt Catch: Install the bolt catch assembly, which allows you to lock the bolt back for maintenance or to clear malfunctions.
3. Installing the Magazine Release: Install the magazine release button, spring, and catch.
4. Installing the Buffer Tube and Stock: Thread the buffer tube into the receiver and install the buffer, buffer spring, and stock.

Choosing the Right Components for a Perfect Build

The AR-10 platform is all about choices. From the caliber to the stock, there is a wide array of options available to the builder. Careful component selection is critical to achieve the desired performance and reliability. This is where the fun begins!

• Caliber: The AR-10 platform is typically chambered in larger calibers than the AR-15. The .308 Winchester is the most common, offering a good balance of power and availability. Other popular calibers include 6.5 Creedmoor, which offers excellent long-range performance, and various .223/5.56 derivatives. Consider the intended use of the rifle when selecting the caliber.
• Upper Receiver: Choose an upper receiver that is compatible with the lower receiver. Be sure to consider the material, length, and features of the upper.
• Bolt Carrier Group (BCG): The BCG is the heart of the AR-10’s operation. Select a BCG that is compatible with the chosen caliber and upper receiver.
• Barrel: The barrel is a critical component. Select a barrel with the appropriate twist rate for the chosen ammunition. Also, consider the length and profile of the barrel.
• Stock: The stock affects the fit, comfort, and handling of the rifle. Choose a stock that fits your shooting style and provides a good cheek weld.
• Handguard: The handguard protects the barrel and provides a platform for accessories. Choose a handguard that is compatible with the upper receiver and provides the desired features.

Safety First: Precautions and Considerations

Building an AR-10 from an AR-10 80% lower requires a strong commitment to safety.

• Gun Safety Basics: Always treat every firearm as if it is loaded. Never point the muzzle at anything you are not willing to destroy. Keep your finger off the trigger until you are ready to shoot. Be sure of your target and what is beyond.
• Proper Storage: When not in use, store the completed lower and other firearm components in a secure location, out of reach of children and unauthorized individuals.
• Function Check: After assembling the lower, perform a function check to ensure that all components are working properly.
• Potential Issues: Be aware of potential problems that may arise during assembly or shooting. Seek professional assistance if you encounter any issues.

Where to Find Your Components

Sourcing parts for your AR-10 build is now easier than ever.

• Online Retailers: Numerous online retailers specialize in firearm parts, including AR-10 80% lowers and LPKs. Research and compare prices. Read reviews before purchasing from any retailer.
• Local Gun Shops: Check your local gun shops for parts. They may also offer assistance.
• Manufacturers: Some manufacturers sell directly to consumers.
• Selecting a Seller: When selecting a seller, consider their reputation, pricing, shipping costs, and return policies.

Conclusion: Embarking on Your Build

Building an AR-10 from an AR-10 80% lower is a rewarding journey that allows shooters a deeper understanding of their firearm. This project requires time, patience, and attention to detail, but the result is a customized rifle that reflects your unique preferences and meets your specific needs. By following this guide, and adhering to safety guidelines, you can embark on your own AR-10 80% lower build with confidence. Building your own firearm can be a hugely satisfying experience!

The AR-10 platform offers a potent combination of power, accuracy, and customization. It gives builders a way to go from an unfinished receiver to a firearm. The world of AR-10s awaits.

Call to Action

Now it’s your time to start! Researching and selecting components for your build is the first step. Consider what you want your AR-10 80% lower build to achieve. Consider your budget and preferences. If you have questions, feel free to leave them in the comments section. Look for online forums and YouTube videos to further your learning!

Good luck with your build!