Once you’ve completed the basics of milling and drilling an 80 lower, there are advanced techniques that can help improve the accuracy, reliability, and overall quality of your build. Here are some steps for those who want to take their 80 lowers build to the next level:
Finishing the Receiver Surface
After completing the main machining, it’s beneficial to finish the receiver surface to prevent wear and corrosion. Some popular methods include:
- Anodizing: This is a process of adding a protective oxide layer to aluminum receivers. Anodizing not only protects against corrosion but also gives a professional finish.
- Cerakote or Powder Coating: These finishes offer both aesthetic appeal and extra protection. Cerakote, in particular, is a ceramic-based coating that adds durability to the receiver’s surface.
Precision Drilling and Milling Tips
Precision is key when drilling and milling your 80 lower. Here are some advanced tips to ensure the highest level of accuracy:
- Use a Calibrated Mill: A drill press or milling machine with adjustable and calibrated settings will allow for precise cuts. While some people use hand drills, a high-quality mill provides better results.
- Invest in Quality End Mills and Drill Bits: Low-cost tools may dull or break during machining. High-quality carbide bits are more durable and produce cleaner cuts, especially with aluminum or other hard materials.
- Practice on Scrap Material First: If you’re new to working with metals, practicing on scrap aluminum or polymer can help build confidence and ensure accuracy.
Fine-Tuning the Fire Control Group Pocket
The fire control group (FCG) pocket is a crucial area for functionality. To optimize it:
- Measure the Pocket Depth: Incorrect pocket depth can lead to malfunctions. Verify the depth with a caliper to ensure compatibility with your fire control components.
- Check for Burrs and Imperfections: Use a deburring tool or fine sandpaper to smooth out any sharp edges or metal burrs, which can affect functionality.
Assembling the Firearm
Once your 80 lower is complete, you can start assembling the firearm. The assembly process will differ depending on the type of firearm you’re building, but here’s a general guide for AR-style builds:
1. Installing the Lower Parts Kit (LPK)
The Lower Parts Kit includes components like the trigger, hammer, safety selector, and pins. Here’s a step-by-step guide for installation:
- Install the Trigger Assembly: Place the trigger, hammer, and corresponding pins into the FCG pocket. Some triggers come pre-assembled, while others may require extra steps for installation.
- Attach the Safety Selector: Insert the safety selector into the lower receiver, followed by the safety detent and spring.
- Install the Grip and Stock: Attach the grip, as it will secure the safety selector in place. Then, install your preferred stock or brace onto the receiver extension.
2. Connecting the Upper Receiver
The upper receiver contains components like the barrel, handguard, and bolt carrier group. To connect the upper and lower receivers:
- Attach the Barrel to the Upper Receiver: Most barrels come pre-drilled for a gas block and gas tube, which are essential for the firearm’s cycling. Secure the barrel nut and ensure the barrel is aligned correctly.
- Install the Bolt Carrier Group (BCG): Insert the BCG and charging handle into the upper receiver. This group houses the firing pin and bolt, which are responsible for chambering and extracting rounds.
- Secure the Upper and Lower Receivers Together: Align the two receivers and use the takedown and pivot pins to lock them in place.
Troubleshooting Common Issues with 80 Lowers
Even with careful planning, some issues may arise during or after assembly. Here are common problems and solutions:
1. Misalignment of the Fire Control Group
If the trigger or hammer feels loose or doesn’t reset properly, the fire control group may be misaligned. This often results from incorrect pocket depth or uneven milling. To fix this:
- Recheck Your Measurements: Use a caliper to ensure the pocket’s depth matches the LPK specifications.
- Add Shims or Washers: If the components are loose, adding small shims or washers can stabilize them.
2. Failure to Cycle
If the firearm doesn’t cycle correctly, it could be due to a misaligned gas block or faulty BCG. Troubleshoot by:
- Inspecting the Gas Block and Tube: Ensure that the gas block and tube align with the barrel’s gas port.
- Checking the BCG and Buffer Spring: Make sure the bolt carrier group moves freely and that the buffer spring provides enough tension to cycle the action.
3. Trigger Issues
A trigger that’s too stiff or doesn’t fire consistently can be due to:
- Improperly Installed Springs: Double-check the trigger and hammer springs to ensure they’re correctly positioned.
- Incorrect Pocket Dimensions: Make sure the FCG pocket has been milled to the correct dimensions, as even slight inaccuracies can impact trigger performance.
Choosing the Right 80 Lower for Your Needs
With various 80 lowers on the market, choosing the right one is essential for a successful build. Consider these factors:
- Material: Aluminum is strong and durable, suitable for heavy-use firearms, while polymer lowers are lighter and easier to machine. Choose based on the intended use of your firearm.
- Compatibility: Make sure the 80 lower matches the upper receiver you plan to use. AR-15 and AR-10 lowers, for instance, are not interchangeable.
- Budget: 80 lowers come in various price ranges. Higher-quality lowers may cost more but offer better durability and reliability.
- Tools and Skill Level: Some lowers are easier to complete than others. For beginners, polymer lowers might be a good choice due to the simpler machining process.
Frequently Asked Questions (FAQs) About 80 Lowers
1. Can I Purchase an 80 Lower Online?
Yes, in many places, you can purchase an 80 lower online without background checks or paperwork since it’s not classified as a firearm until it’s fully milled. However, some states have restrictions, so be sure to check local regulations.
2. Do I Need a Specific License to Build My Own Firearm Using an 80 Lower?
In the U.S., at a federal level, individuals don’t need a specific license to complete an 80 lower and build a personal firearm. However, the firearm must not be sold or transferred without complying with federal and state laws. Always verify the requirements in your jurisdiction.
3. What Happens if I Make a Mistake While Machining the 80 Lower?
Mistakes during machining can render the lower receiver non-functional. It’s possible to fix some errors by welding or using epoxy for minor imperfections, but larger mistakes may require you to start over with a new 80 lower.
4. Can I Add a Serial Number to My Completed 80 Lower?
Yes, you can engrave a serial number on a completed 80 lower for personal tracking. In some states, it’s legally required to add a serial number, especially if you intend to transfer or transport the firearm.
Pros and Cons of Building a Firearm with an 80 Lower
Here’s a quick summary of the benefits and drawbacks of using an 80 lower to build your firearm:
Pros:
- Full Customization: Allows for a completely personalized firearm with hand-selected components.
- Privacy: Depending on your location, an 80 lower may allow for a firearm without registration or a serial number.
- Cost Savings: Often more affordable than purchasing a complete firearm, especially if you already own the necessary tools.
Cons:
- Skill and Precision Required: Completing an 80 lower requires careful machining, which may be challenging for beginners.
- Legal Gray Areas: In some regions, building an 80 lower firearm has specific regulations or restrictions that can be complex to navigate.
- No Warranty: If the firearm malfunctions, there’s no manufacturer warranty, meaning any repairs or adjustments are your responsibility.
Conclusion
Building a firearm using an 80 lower is a rewarding endeavor that offers firearm enthusiasts greater freedom in customization, privacy, and learning about firearm mechanics. However, this process requires a significant time investment, careful attention to detail, and adherence to local laws. For those willing to put in the work, completing an 80 lower can result in a highly personalized firearm built to exact specifications.
Whether you’re looking to save money, enjoy the challenge of assembly, or create a unique, customized firearm, an 80 lower can be an ideal starting point. Always prioritize safety, accuracy, and compliance, and you’ll find that building with an 80 lower can be both satisfying and educational.
