Building an AR-15 or AR-9: What You Need to Know About 80% Lowers

Business

So, you’re thinking about building your own AR-15 or AR-9? Awesome choice! Whether you’re a seasoned builder or new to the DIY firearms world, starting with an 80% lower receiver is a great way to get hands-on, customize your rifle or pistol, and learn more about how these firearms actually work. But before you dive in, let’s talk about the essentials—what 80 lowers are, why they’re so popular, and what you’ll need to get started.

Wait, What Exactly Is an 80% Lower?

If you’re new to the game, the term 80% lower might sound a bit confusing. Essentially, an 80% lower receiver is a partially finished lower receiver that isn’t legally classified as a firearm—yet. It’s called “80%” because it’s about 80% complete, missing the machining required to house the fire control group (trigger, hammer, and safety).

This means you’ll need to do some milling and drilling to turn it into a functional part of your AR-15 or AR-9. Once completed, it becomes the core component of your firearm, connecting all the other parts together.

AR-15 vs. AR-9: Which One Are You Building?

Here’s where things get interesting. The AR-15 and AR-9 are similar in design, but they serve different purposes.

  • AR-15: Chambered for rifle calibers like .223/5.56, this platform is perfect for hunting, home defense, and target shooting.
  • AR-9: A pistol-caliber carbine (PCC), typically chambered in 9mm. It’s compact, easier to shoot, and ideal for close-quarters shooting or range fun.

Your choice will influence everything, from the type of 80% lower you need to the components you’ll use.

Why Start with an 80% Lower?

So, why go the DIY route? There are plenty of good reasons.

  1. Customization Galore: Building from an 80% lower receiver lets you create a firearm tailored to your needs. Want a lightweight AR-15 for competition shooting? Done. Need a compact AR-9 for home defense? Easy. You’re in control of every detail.
  2. It Can Save You Money: When you buy parts individually, you can prioritize where to spend your money. Invest in a high-quality trigger while saving on the stock—it’s up to you.
  3. Learn as You Build: Completing an 80% lower is an educational experience. You’ll walk away knowing exactly how your firearm works, which is invaluable for maintenance and troubleshooting.
  4. Privacy: In many states, 80% lowers aren’t legally classified as firearms until completed. This means you can buy one without the usual paperwork or FFL transfer (just check your local laws first).

Tools You’ll Need to Complete Your 80% Lower

Now, let’s talk tools. Completing an 80% lower does require some equipment, but don’t worry—it’s all pretty straightforward.

The Essentials

  • 80% Lower Jig Kit: This is your guide, helping you mill and drill the receiver accurately.
  • Drill Press or Hand Drill: For drilling the necessary holes.
  • Router or Milling Machine: Used to machine out the fire control cavity.
  • Vise: Keeps your lower receiver secure during the process.
  • Safety Gear: Always wear safety glasses, gloves, and hearing protection.

AR-15 or AR-9? Choose the Right 80% Lower

Not all 80% lowers are created equal! The lower receiver you need depends on the firearm you’re building.

  • AR-15 80% Lowers: Designed for rifle calibers like .223 or 5.56. These are compatible with standard AR-15 parts and uppers.
  • AR-9 80% Lowers: Specifically designed for pistol calibers like 9mm. They often require proprietary parts, such as a 9mm bolt carrier group and a dedicated buffer system.

Pro Tip: Double-check compatibility between your lower receiver and the upper assembly you’re planning to use. Mixing and matching parts from different platforms can lead to headaches.

The Building Process: What to Expect

Here’s a quick rundown of what you’ll do when completing an 80% lower:

  1. Set Up Your Jig: Secure your lower receiver in the jig kit. This will guide your drilling and milling.
  2. Drill Pilot Holes: Use a drill press or hand drill to create the holes for the trigger, hammer, and safety selector.
  3. Mill the Fire Control Cavity: Carefully machine out the area where the trigger group will go. Take your time—precision matters.
  4. Deburr and Clean: Smooth out any rough edges and clean the receiver to remove metal shavings.
  5. Assemble Your Lower Receiver: Install the lower parts kit (trigger, magazine catch, buffer tube, etc.).
  6. Attach the Upper Receiver: Join the lower and upper assemblies using the takedown and pivot pins.

Once everything’s put together, test your firearm for functionality before heading to the range.

Legal Stuff You Should Know

Before you start, make sure you understand the laws in your area.

  • Federal Law: In most states, it’s legal to build a firearm for personal use without serializing it. However, you cannot sell or transfer it without proper licensing.
  • State Laws: Some states have restrictions on 80% lowers or require serialization once completed. Check your state and local regulations to stay compliant.

Final Thoughts: Why Build Your Own?

Building an AR-15 or AR-9 from an 80% lower is more than just assembling a firearm—it’s about the experience, the education, and the satisfaction of creating something with your own hands. Whether you’re crafting a long-range AR-15 or a compact AR-9, starting with an 80% lower receiver gives you the freedom to build exactly what you need.