The Complete Guide to 80% Lowers: Building Your Own Firearm

In recent years, 80% lowers have gained significant traction among firearm enthusiasts. These unfinished lower receivers offer the unique ability to build a firearm from the ground up, offering both a rewarding challenge and the ability to customize every aspect of the weapon. However, with this freedom comes an understanding of the legal, technical, and practical aspects of completing an 80% lower. This guide will explore the ins and outs of 80% lowers, from what they are to the step-by-step process of completing one, and the legal considerations you need to be aware of.

What is an 80% Lower?

An 80% lower refers to an unfinished lower receiver for a firearm, typically made of aluminum or polymer. The term “80%” indicates that approximately 80% of the machining has already been done by the manufacturer, leaving the remaining 20% for the individual to finish. This unfinished component is not considered a firearm by the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) until it is fully completed. Essentially, it’s a receiver that requires additional work—such as drilling pinholes, cutting the fire control pocket, and finishing the buffer tube threads—to become functional.

The main attraction of  80% lowers is that they are not legally classified as firearms until they are completed. This makes them easier to purchase than a fully completed firearm, as they are not subject to the same regulations or background checks. However, once the lower is finished and assembled into a functional firearm, it is subject to all relevant firearm laws.

Why Choose 80% Lowers?

1. Customization and Control

One of the key benefits of building a firearm from an 80% lower is the level of customization it offers. By assembling the firearm yourself, you have the freedom to choose each individual component based on your preferences and needs. From the trigger and stock to the barrel and grip, the choice is yours. You can build a firearm that suits your specific purposes, whether it’s for target shooting, hunting, home defense, or collecting.

This level of control over the design also allows you to make modifications based on personal comfort, ergonomic preferences, and desired performance. Many enthusiasts enjoy the challenge of choosing quality parts to create a custom, one-of-a-kind firearm.

2. Learning Experience

For individuals interested in gunsmithing, building a firearm from an 80% lower provides a valuable learning experience. It allows you to understand how a firearm works from the inside out. The process of completing the lower and assembling the parts gives you hands-on knowledge of the inner mechanics of a gun.

The ability to learn about firearms in a practical way can be immensely satisfying for those who enjoy working with tools and machinery. Additionally, once the lower receiver is completed, you gain a deeper understanding of the maintenance, upkeep, and troubleshooting required to ensure your firearm operates smoothly.

3. Cost-Effectiveness

While purchasing a pre-assembled firearm may seem easier, building a firearm from an 80% lower can save you money. Pre-assembled guns often come with a premium price tag, as you’re paying not only for the materials but also for assembly, branding, and retail markup. When you build your own firearm, you can save a significant amount of money by choosing individual parts that fit your budget.

Although you will need to purchase additional tools—such as a drill press or milling machine—these can be used for future projects, making the overall cost even more economical in the long term. Once you have the proper equipment, you can continue to complete more lowers for future firearms.

4. Privacy

Another appeal of 80% lowers is the level of privacy they offer. Since they are not considered firearms until they are completed, there is no need to undergo a background check or register the component when purchasing it. This makes it easier for individuals who prefer to keep their firearms ownership private. However, once the lower is completed and becomes a functional firearm, it is subject to the same registration and background check requirements as any other gun.

Legal Considerations for 80% Lowers

While 80% lowers offer certain freedoms when it comes to building your own firearms, there are several important legal aspects to be aware of:

1. Federal Law

Under federal law, an 80% lower is not classified as a firearm, as it cannot expel a projectile by the action of an explosive until it is finished. This means that it is legal to buy and sell 80% lowers without the need for a background check or serial number. However, once the lower is completed and becomes a functional firearm, it must be serialized, and you must comply with all local, state, and federal firearm regulations.

In addition, the Gun Control Act of 1968 and National Firearms Act (NFA) still apply once the firearm is assembled. These laws regulate aspects such as the transfer and registration of firearms and require individuals to have a serial number on their completed firearm.

2. State Laws

While federal law provides a general framework for 80% lowers, state laws can vary significantly. Some states have stricter regulations than others when it comes to 80% lowers. For example, in states like California, New York, and New Jersey, there are laws governing the sale, purchase, and completion of 80% lowers.

In some states, a completed firearm may be required to have a serial number or be registered with the local authorities. States like California, which has strict “ghost gun” laws, require individuals to register their completed firearms and may have additional requirements for 80% lowers. In states with more relaxed laws, such as Texas or Florida, individuals can often purchase 80% lowers with fewer restrictions.

It’s crucial to research and understand the laws in your specific state to avoid running afoul of local firearm regulations. Non-compliance with state or local laws can lead to serious legal consequences.

3. Serialization and Registration

Once you complete your 80% lower and it becomes a functional firearm, you are required to serialize it in most states. A serial number is a unique identification number assigned to the firearm, which can help law enforcement track the gun in case it is lost or stolen. The process of serializing your completed firearm is relatively straightforward, and there are a variety of options for engraving or stamping the serial number onto the lower receiver.

In some states, you may be required to register the firearm with the local authorities. Even if your state does not require registration, it may be a good idea to keep a record of your serialized firearm for insurance purposes or in the event of a legal dispute.

How to Complete an 80% Lower

Completing an 80% lower requires a few basic tools and some careful attention to detail. Here is an overview of the steps involved in completing an 80% lower:

1. Gather the Necessary Tools

To finish an 80% lower, you will need a few essential tools:

• Drill press or milling machine: A drill press is essential for drilling the pin holes and milling the fire control pocket. A milling machine is more accurate but can be more expensive.
• 80% lower jig: The jig is a guide that helps align the lower receiver during the machining process, ensuring that everything is drilled and milled in the correct locations.
• Drill bits and end mills: These will be used to drill the necessary pin holes and to mill the fire control pocket.
• Clamps and safety gear: Use clamps to secure the lower and safety gear, including gloves and eye protection, to ensure safe operation.

2. Set Up the Jig

The first step is to securely clamp the 80% lower into the jig. The jig will guide the tools during the machining process and ensure the holes are drilled accurately.

3. Drill the Pin Holes

Next, you will need to drill the pin holes for the trigger, hammer, and safety components. It is important to drill these holes precisely, as misalignment could prevent proper assembly of the firearm.

4. Mill the Fire Control Pocket

The fire control pocket is one of the most critical areas of the lower receiver, as it houses the trigger mechanism. Milling this area involves removing material from the lower receiver using a mill or drill press. Precision is essential during this step to ensure the trigger mechanism functions correctly.

5. Finish the Lower

Once the necessary holes and pocket are milled, the final step is to clean up any rough edges and perform a function check to ensure everything fits together properly. Afterward, you can apply a protective coating or finish, such as anodizing, to prevent corrosion.

6. Assemble the Firearm

Once the 80% lower is completed, you can begin assembling the rest of the firearm, which includes installing the trigger group, stock, and barrel. Conduct a function check before firing to ensure that all parts work smoothly and safely.

Conclusion

80% lowers provide a unique and rewarding opportunity for firearm enthusiasts to build their own custom guns. They offer a level of personalization, learning, and cost savings that attracts many hobbyists and DIY enthusiasts. However, building a firearm from an 80% lower comes with legal responsibilities. It’s crucial to understand the laws surrounding 80% lowers in your state and comply with all federal, state, and local firearm regulations. By following the proper steps and using the right tools, you can build a firearm that is both functional and uniquely your own.