Building an AR-15 from an 80 lower is a rewarding project for firearm enthusiasts. It allows you to customize your rifle to fit your specific needs and gives you a deeper understanding of how your firearm functions. In this comprehensive guide, we’ll walk you through the entire process—from choosing your components to completing your build.
Whether you’re a seasoned DIYer or a first-time builder, this guide will cover everything you need to know, including tools, tips, and legal considerations.
What Is an 80% Lower?
An 80% lower receiver is a partially machined AR-15 lower receiver. It lacks the machining required for the fire control group (trigger, hammer, and safety selector). Since it is not considered a firearm under federal law, you can purchase it without going through an FFL (Federal Firearms License) dealer. However, completing an 80% lower receiver transforms it into a fully functional firearm component, subject to state and federal laws.
Why Build an AR-15 Using an 80% Lower?
- Customization: Building an AR-15 from scratch lets you tailor it to your preferences, whether for hunting, target shooting, or home defense.
- Cost Savings: Completing an 80 percent lower can be more cost-effective than buying a fully assembled rifle.
- Educational Value: The process teaches you the inner workings of an AR-15, enhancing your understanding and maintenance skills.
- Privacy: Since 80% lowers are not classified as firearms until completed, they can be purchased without paperwork in many states (check local laws for compliance).
Tools and Materials Needed
Before starting your build, gather the following tools and materials:
Tools:
- Drill Press or Hand Drill: To mill out the fire control cavity.
- Router or Mill: For precision cutting.
- 80% Lower Jig Kit: Guides you through the machining process.
- Drill Bits and End Mills: Usually included with the jig.
- Torque Wrench: Ensures parts are properly tightened.
- Armorer’s Wrench: Designed for AR-15 components.
- Vise: Secures your workpiece during milling and assembly.
- Safety Equipment: Safety glasses, gloves, and hearing protection.
Materials:
- 80% Lower Receiver
- Upper Receiver Assembly
- Lower Parts Kit (LPK): Includes trigger, safety selector, and other small parts.
- Buffer Tube Assembly
- Barrel
- Bolt Carrier Group (BCG)
- Handguard
- Stock or Pistol Brace
- Magazines
Step-by-Step Guide
1. Review Local and Federal Laws
Before starting your build, ensure you are in compliance with all local, state, and federal regulations. While it’s legal to build a firearm for personal use in many areas, specific laws regarding 80% lower receivers and completed firearms vary.
2. Set Up Your Workspace
Create a safe and organized workspace with ample lighting. Ensure your vise and tools are securely mounted to prevent accidents. Safety is critical when using power tools.
3. Prepare the 80% Lower
Unbox your 80% lower receiver and inspect it for any imperfections. Clean it thoroughly to remove oils or debris that could interfere with machining.
4. Attach the Lower to the Jig
Place your 80% lower receiver into the jig kit. The jig is your blueprint, guiding your drill and router to remove the correct material. Follow the manufacturer’s instructions to secure the lower in the jig.
5. Drill Pilot Holes
Using the specified drill bits from your jig kit, drill pilot holes for the fire control group. Ensure your drill press or hand drill is set to the correct speed to avoid overheating or damaging the lower.
6. Mill the Fire Control Cavity
Switch to the end mill bit and carefully mill out the fire control cavity. This step requires patience and precision. Take small passes to avoid damaging the receiver or tools. Regularly check your progress against the jig’s guidelines.
Pro Tip: Use cutting fluid to reduce friction and prevent overheating.
7. Deburr and Clean the Lower
Once milling is complete, inspect the fire control cavity for rough edges. Use a file or deburring tool to smooth out any burrs. Thoroughly clean the receiver to remove metal shavings and dust.
8. Assemble the Lower Receiver
With the machining complete, it’s time to assemble the lower receiver using the Lower Parts Kit (LPK). Follow these steps:
- Install the Trigger Group: Place the trigger, hammer, and disconnector into the fire control cavity and secure them with the provided pins.
- Install the Magazine Catch and Bolt Catch: Insert the magazine catch and bolt catch assemblies into their respective slots.
- Attach the Safety Selector: Install the safety selector and grip.
- Install the Buffer Tube and Stock: Thread the buffer tube into the lower receiver, insert the buffer spring and buffer, and attach the stock or brace.
9. Attach the Upper Receiver
The upper receiver assembly typically includes the barrel, handguard, and bolt carrier group. Follow these steps:
- Attach the Barrel: Insert the barrel into the upper receiver and secure it with the barrel nut. Use a torque wrench to tighten to the manufacturer’s specifications.
- Install the Handguard: Slide the handguard over the barrel and secure it to the upper receiver.
- Insert the Bolt Carrier Group (BCG): Slide the BCG into the upper receiver.
- Attach the Charging Handle: Insert the charging handle above the BCG.
- Join the Upper and Lower Receivers: Use the takedown and pivot pins to connect the upper and lower receivers.
10. Test Functionality
Before firing your AR-15, perform a series of function tests to ensure it operates correctly:
- Safety Check: Confirm that the safety selector blocks the trigger when engaged.
- Trigger Reset: Pull the trigger and hold it back. Cycle the charging handle, then release the trigger. You should hear a distinct “click.”
- Bolt Operation: Ensure the bolt cycles smoothly and locks back when the magazine is empty.
11. Take It to the Range
After confirming functionality, take your AR-15 to a qualified range for live-fire testing. Start with a few rounds to ensure reliability before fully loading magazines.
Tips for a Successful Build
- Practice Patience: Rushing through the milling or assembly process can lead to mistakes.
- Double-Check Measurements: Precision is key to ensuring a safe and functional firearm.
- Invest in Quality Tools: High-quality tools and components make the process smoother and more enjoyable.
- Keep It Legal: Always follow federal and state laws regarding firearm manufacturing and ownership.
Frequently Asked Questions
Is it hard to complete an 80% lower?
While it requires patience and attention to detail, completing an 80% lower receiver is achievable with the right tools and guidance.
Can I sell the firearm I build?
Federal law prohibits building firearms with the intent to sell without a manufacturing license. Always check local laws for additional restrictions.
What are the advantages of using an 80% lower?
An 80 percent lower offers customization, cost savings, and privacy compared to buying a factory-assembled firearm.
Building an AR-15 from an 80% lower is a fulfilling experience that gives you a custom rifle and a sense of accomplishment. By following this guide and using quality components, you can create a reliable, high-performance firearm tailored to your needs.
Ready to start your build? Visit Thunder Tactical for premium 80% lowers and AR build kits!