What Exactly Is an AR-10 Eighty Percent Lower Receiver?
Building your own rifle can be a deeply rewarding experience. It allows for unparalleled customization, a deeper understanding of the mechanics, and the satisfaction of creating something unique. For enthusiasts of the AR platform, the AR-10, or the larger-caliber AR-style rifle, offers the power and versatility for a wide range of applications, from hunting to long-range shooting. This article will serve as your comprehensive guide to building an AR-10 using an eighty percent lower receiver. This guide will walk you through everything from choosing the right components to assembling your custom AR-10, all while emphasizing safety and legal considerations.
At the heart of any AR-10 rifle lies the lower receiver. This component is the legally controlled firearm, the serialized part that defines the weapon. An eighty percent lower, however, is different. It’s a partially completed lower receiver, lacking the final machining necessary to accept the fire control group (trigger, hammer, safety), and other internal components. This distinction is crucial, because in many jurisdictions, an eighty percent lower is not considered a firearm under federal law.
Think of it like a blank canvas. You receive a raw piece of metal, usually aluminum, and you must finish the milling, drilling, and shaping to transform it into a functional lower receiver. This presents an opportunity to build a rifle that is perfectly tailored to your specific needs and preferences.
The legal landscape surrounding eighty percent lowers can be complex and varies significantly depending on where you live. It’s imperative that you fully understand and comply with all federal, state, and local laws and regulations. Failure to do so can have serious consequences. Research your local laws thoroughly before starting any build.
Choosing the Right AR-10 Eighty Percent Lower
Selecting the appropriate eighty percent lower is a critical first step in the building process. Several factors should influence your decision, beginning with the material.
Material Options
Aluminum is the most common material for AR-10 lowers. It’s lightweight, durable, and relatively easy to machine. The specific type of aluminum (e.g., 7075-T6, 6061-T6) affects the receiver’s strength and resistance to wear. Generally, 7075-T6 is preferred for its superior strength.
While aluminum is standard, consider other materials if they are available and suit your preferences.
Compatibility Considerations
Beyond the material, compatibility is paramount. The AR-10 platform has evolved over time, and not all parts are universally interchangeable. Make sure your eighty percent lower is designed to work with AR-10 components, not AR-15 parts.
Pay close attention to the caliber you intend to use. The AR-10 platform is frequently chambered in .308 Winchester, but it can also accommodate other calibers, such as 6.5 Creedmoor, or even larger cartridges. Your eighty percent lower must be compatible with the caliber you choose.
Features and Aesthetics
Consider features. Does it have engraved markings? What about the aesthetics? Do you like the look and feel?
Ultimately, the goal is to select an eighty percent lower that provides a solid foundation for your rifle. Research different manufacturers, read reviews, and compare specifications before making your final decision. Choosing a reputable manufacturer increases your chances of a successful build.
Tools and Equipment You’ll Need
Finishing an eighty percent lower requires specific tools and equipment. This is not something you can accomplish with a basic screwdriver set. Investing in the right tools is essential for achieving a professional-looking and functional result.
The most critical tool is a jig. An eighty percent lower jig is a specialized device that holds the lower receiver securely during the machining process. It guides the drill and end mill, ensuring accurate holes and cuts. There are jigs for both drill presses and milling machines.
A drill press or milling machine is essential for precise drilling and milling. While a drill press is often sufficient, a milling machine provides greater control and is generally preferred for complex cuts.
You’ll need a variety of drill bits and end mills. Refer to the manufacturer’s instructions for your eighty percent lower and jig to determine the specific sizes required. Purchase high-quality drill bits and end mills, as they’ll cut the process time and improve the outcome.
Clamps are essential for securing the jig and lower receiver to the drill press or milling machine table.
A sturdy vise is useful for holding the lower receiver securely during certain operations.
Safety glasses are non-negotiable. Protect your eyes from flying metal fragments.
Cutting oil or a suitable lubricant is essential for lubricating the drill bits and end mills, reducing friction, and preventing overheating.
Deburring tools, such as a deburring tool, will be used to remove sharp edges and burrs from the newly machined holes.
Optional tools could be a work bench, measuring tools (calipers or a depth gauge).
Ensure you have a safe workspace. Before you begin, take a moment to understand the process and plan accordingly. This build is a precision activity. Be prepared.
The Finishing Process: Step-by-Step
The specific finishing process for your eighty percent lower will depend on the jig and any instructions from the manufacturer. However, the general steps are consistent. Always consult the instructions provided with your specific jig and lower receiver. Safety first.
Attaching the Jig
Securely attach the jig to the lower receiver according to the manufacturer’s instructions. Ensure that everything is properly aligned and clamped.
Machining the Fire Control Group Pocket
Using the jig as a guide, carefully drill and mill out the pocket that will house the trigger, hammer, and other fire control components.
Drilling Pin Holes
Using the appropriate drill bits and the jig, drill the holes for the trigger and hammer pins. These holes must be precisely aligned for the fire control group to function correctly.
Drilling the Selector Detent Hole
Drill the hole for the safety selector detent, which allows the safety selector to function properly.
Deburring and Cleaning
Once all the machining is complete, carefully deburr all the holes and edges to remove any sharp edges or burrs. Clean the lower receiver thoroughly to remove any metal shavings.
Throughout this process, go slow. Take your time. Check your work frequently.
Assembling Your AR-10 Rifle
Once your eighty percent lower is complete, you can begin the assembly of your AR-10. This is where your custom rifle starts to take shape.
You will need several components, including:
- Upper receiver
- Barrel
- Bolt carrier group
- Handguard
- Stock
- Buffer tube
- Buffer spring
- Buffer
- Fire control group (trigger, hammer, disconnector, springs, and pins)
- Pistol grip
- Charging handle
- Magazine release
- Safety selector
- Forward assist
- Various pins, springs, and detents
Start by attaching the upper and lower receivers. Ensure they fit together properly and that the takedown pins align correctly.
Install the fire control group. This involves carefully inserting the trigger, hammer, disconnector, and associated pins and springs.
Assemble the buffer tube and stock. Thread the buffer tube into the lower receiver and install the buffer spring and buffer. Attach the stock to the buffer tube.
Install the handguard, using the appropriate mounting system for your chosen handguard.
Attach the barrel to the upper receiver, ensuring proper torque. Install the bolt carrier group into the upper receiver.
Complete the final assembly by installing the pistol grip, charging handle, magazine release, safety selector, and forward assist.
Be patient and refer to the instructions provided with each component. Ensure everything is functioning correctly before taking the rifle to the range.
Safety and Legal Considerations: A Final Reminder
Safety is paramount at all times when building and operating any firearm. Always:
- Wear eye protection.
- Keep the muzzle pointed in a safe direction.
- Treat every firearm as if it were loaded.
- Never point a firearm at anything you are not willing to destroy.
- Be sure of your target and what is beyond it.
- Keep your finger off the trigger until ready to fire.
- Be certain the firearm is unloaded before cleaning or servicing.
- Only use the correct ammunition.
Always prioritize safety.
As mentioned previously, it’s critical to understand and comply with all applicable federal, state, and local laws and regulations regarding firearm ownership, manufacturing, and modifications. Laws are subject to change. It is your responsibility to stay informed. Consult with a qualified legal expert if you have any questions or concerns about the legality of your build or any of its components.
In Conclusion
Building an AR-10 from an eighty percent lower is an engaging project. It provides a great deal of satisfaction. With careful planning, the right tools, and attention to detail, you can create a custom rifle that meets your exact needs.
Before you start, conduct your research, choose your components wisely, and always prioritize safety and legality. Remember to check your local laws regarding eighty percent lowers, to be sure that the finished product is compliant.
Remember to practice responsible gun ownership at all times.
