Completing an 80% lower receiver is a hands-on project that allows firearm enthusiasts to customize their builds while gaining a deeper understanding of firearm mechanics. However, turning a partially machined 80% lower into a functional firearm component requires precision, the right tools, and proper technique.
This comprehensive guide will walk you through the tools, tips, and step-by-step process to help you confidently complete your 80 percent lower receiver. Whether you’re a seasoned builder or a beginner, this guide will provide everything you need to get started.
What Is an 80% Lower Receiver?
An 80% lower receiver is a partially finished AR-15 or AR-10 lower receiver. Since it has not been fully machined to house the fire control group (trigger, hammer, and safety), it is not legally considered a firearm in most jurisdictions. However, once completed, it becomes a key component of a fully functioning rifle or pistol.
Building a firearm from an 80% lower is popular among enthusiasts for several reasons:
- Privacy: You can purchase it without federal paperwork in many areas.
- Customization: You can tailor your firearm to meet specific needs.
- Education: Completing an 80% lower teaches you valuable gunsmithing skills.
Before proceeding, ensure you’re aware of the local, state, and federal laws regarding the completion of an 80% lower receiver.
Tools Needed to Complete an 80% Lower
Successfully completing an 80% lower requires specialized tools and equipment. Investing in the right tools will save time, prevent errors, and ensure a professional finish.
1. Drill Press or Hand Drill
A drill press offers stability and precision for drilling the fire control group’s holes. A hand drill can work but requires extra care.
2. Router or Milling Machine
These tools are essential for removing material from the fire control cavity. Routers are user-friendly for beginners, while milling machines offer advanced precision.
3. 80% Lower Jig Kit
A jig kit serves as a guide, ensuring accuracy when milling and drilling. It includes plates and templates to outline where material should be removed.
4. Drill Bits and End Mills
Most jig kits come with the necessary drill bits and end mills. Check the manufacturer’s recommendations to ensure compatibility.
5. Vise
A sturdy vise secures the 80% lower during machining, preventing movement that could lead to mistakes or accidents.
6. Torque Wrench
A torque wrench ensures all fasteners are tightened to the correct specifications.
7. Safety Equipment
- Safety Glasses: Protects your eyes from metal shavings.
- Gloves: Provides grip and shields your hands from sharp edges.
- Hearing Protection: Essential when using power tools.
Step-by-Step Guide to Completing Your 80% Lower Receiver
Step 1: Set Up Your Workspace
Choose a clean, well-lit area with a sturdy workbench. Organize your tools and materials to avoid unnecessary interruptions during the process. Safety should be a priority—wear your protective gear and keep distractions to a minimum.
Step 2: Inspect and Prepare Your 80% Lower
Before starting, inspect your 80 percent lower receiver for any imperfections or defects. Clean it thoroughly to remove oils or debris that could interfere with machining.
Step 3: Secure the Lower in the Jig
Position your 80% lower receiver into the jig according to the manufacturer’s instructions. The jig kit will guide you through drilling and milling with precision.
- Tip: Tighten the jig firmly in your vise to prevent movement during machining.
Step 4: Drill Pilot Holes
Using the jig’s templates, drill pilot holes for the fire control group (trigger, hammer, and selector). A drill press ensures consistent depth and alignment.
- Tips for Drilling:
- Use cutting fluid to reduce heat and prolong drill bit life.
- Apply consistent pressure to avoid damaging the material.
- Drill slowly for maximum accuracy.
Step 5: Mill the Fire Control Cavity
Switch to an end mill bit and use your router or milling machine to remove material from the fire control cavity. Take your time to avoid over-milling, which can weaken the receiver.
- Tips for Milling:
- Remove material in small increments to maintain control.
- Regularly check your progress against the jig’s guidelines.
- Clean metal shavings frequently to ensure smooth operation.
Step 6: Deburr and Clean the Receiver
Once the milling is complete, inspect the fire control cavity for sharp edges or burrs. Use a deburring tool or fine file to smooth out any imperfections.
- Clean the receiver thoroughly to remove metal shavings and dust.
- Test the fire control group’s fit to ensure proper dimensions.
Step 7: Install the Lower Parts Kit (LPK)
With the 80% lower receiver completed, it’s time to assemble the fire control group using the Lower Parts Kit (LPK).
Key Steps:
- Trigger and Hammer: Insert the trigger and hammer into the cavity and secure them with the provided pins.
- Safety Selector: Install the safety selector along with the pistol grip.
- Magazine Catch and Bolt Catch: Attach these components to their respective slots.
- Buffer Tube: Screw the buffer tube into the lower receiver and insert the buffer spring and buffer.
Step 8: Test Fit and Function
Before attaching the upper receiver, perform a basic function check:
- Ensure the safety selector operates correctly.
- Test the trigger and hammer mechanism for smooth operation.
- Check that all parts fit securely without wobbling.
Tips for a Successful Completion
1. Take Your Time
Rushing through the process can lead to mistakes. Approach each step methodically and double-check your work.
2. Use Quality Tools
Investing in high-quality tools and components can save you time and frustration. Cheap tools may break or cause inaccuracies during machining.
3. Follow Manufacturer Instructions
Each jig kit and 80% lower receiver is designed slightly differently. Always refer to the manufacturer’s guide for specific instructions.
4. Keep Your Workspace Organized
A cluttered workspace increases the risk of accidents. Keep tools within reach and remove any unnecessary items.
5. Practice on a Test Piece
If you’re new to machining, consider practicing on a scrap piece of aluminum before working on your 80% lower receiver.
Frequently Asked Questions
Is it legal to complete an 80% lower receiver?
In most states, completing an 80% lower receiver for personal use is legal. However, laws vary by location, so always check your local and state regulations before proceeding.
Can I sell a firearm built from an 80% lower?
No. Federal law prohibits manufacturing firearms with the intent to sell without a license. Firearms built from 80% lowers are intended for personal use only.
What’s the best material for an 80% lower?
Aluminum is the most popular choice due to its strength, durability, and lightweight nature. Polymer lowers are also available for those looking for an easier machining experience.
Conclusion
Completing an 80% lower receiver is a rewarding process that gives you a custom firearm tailored to your needs. By following this guide and using the right tools, you can confidently transform your 80 percent lower into a functional AR-15 or AR-10 lower receiver. Remember to take your time, prioritize safety, and adhere to all local and federal laws.