What Are 80% Lowers?


This is a guest post by Almo Gregor

The U.S. has some weird gun laws. Though we have more gun freedom than any other nation, we still have some odd laws. Take a look at 922 R, suppressor laws, and the way we determine what portion of a gun is a gun. With AR-15s and most handguns, the serialized lower receiver is the actual firearm. That one piece of a gun is considered the firearm. It’s treated no different from a complete AR-15, Glock, 1911, or any other firearm in the eyes of the federal government.

Every other gun part can come straight to your door, but an AR-15 lower requires an FFL. Another unique part of American firearms law is 80% lower receivers.

Going 80 (and Following the Law)

Due to the definition of firearms in the United States, an AR-15 80% lower is not considered a firearm. Its receivers are lowers that do not have a milled fire control group. They are considered nothing more than chunks of aluminum or polymer, legally speaking. They do not require an FFL to transfer, and they can be mailed directly to your door. In the eyes of the law, you are building a firearm from scratch with 80% lowers.

An 80% lower becomes a firearm as soon as you begin the milling process. Once the first drill bit or endmill scratches the surface of an 80% lower receiver or frame, you have created a firearm. Once it becomes a firearm, it is now subject to all federal and state laws. Federally, it is not illegal to build your firearm as long as you follow all federal laws. State laws may vary; but as far as I know, all 50 states allow the construction of firearms. You should always check state and local laws before building any firearm.

Why Build with an 80% Lower?

There are several reasons to go with an 80% lower versus a standard stripped lower receiver. The biggest reason is the fun factor in finishing an 80% lower receiver. It takes building a rifle to the next level of difficulty and challenge. In California, it’s easier to build your rifle than to find a California Compliant AR-15 after the bullet button ban.

Other folks may appreciate their privacy when it comes to firearms. In some situations, due to the fear of changing firearms laws, regular lower receivers may not be easily available. And if they are, they may be quite expensive due to sudden demand.

All are valid reasons that have allowed 80% lowers to become popular.

Material Selection

The AR-15 is a very popular rifle, with more options than I can possibly list. When it comes to AR-15 80% lower receivers, you also have a broad selection.


Most AR-15 receivers are made from aluminum, including 80% lowers. Aluminum has proven to be a sturdy and lightweight material that is perfect for the AR-15. There are two types of aluminum lowers — 6061 or 7075 T6.

The T6 designation means they are heat treated. The big difference between the two is that 7075 is the stronger material. 6061 is “softer” and not as strong. 6061 is easier to mill when the time comes to turn your 80% lower into an actual lower.

Forged Receivers

You can go with standard Mil-Spec-style forged lower receivers. This is the most common option for lower receivers.

Forged receivers are the strongest lowers available and also the most affordable. They start life as aluminum blocks that are hammered into an AR-15 shape and refined through a CNC machine.


Billet receivers start life as one solid block of aluminum. That solid block is then put through a CNC machine to refine it into an AR-15 lower receiver.

Forged lowers have a higher tensile strength, but the difference isn’t something you’ll ever notice. Billet receivers look cool — they have sharp and angular lines and often have built in trigger guards.


Over the last few years, the use of polymers in AR-15 style firearms has risen substantially. Since lower receivers aren’t exposed to significant force, the lower can be made of polymer safely.

Polymer are the lightest lower receivers and are, by far, the easiest to mill. The issue with polymer is the weak points around the buffer tube assembly. Research on the manufacturer to ensure they produce a quality product.

Each has their advantages and disadvantages. You can never go wrong with a standard Mil-Spec-style forged lower. It’s typically the most affordable and supported route.

From 80 to 100

To finish a lower receiver, you need to mill out the relevant areas to allow the installation of a fire control group. To do so, you need a jig. It acts like a template that guides you as you mill your lower receiver or frame.

Jigs vary in style and quality. Some are multi-plate systems that are designed to make milling as fast as possible. Other jigs are nothing more than a vinyl sticker. The better the jig, the faster you’ll be able to mill and often the easier it will be to mill an 80% lower into a complete lower.


You need to do tooling to the actual milling. Most AR-15 80% lower receivers utilize either a drill press or a router, with proper bits or end mills. Different tooling will use different jigs.

So if you buy a jig made for a drill press, you can’t use a router to finish it. You also need a tool that is powerful enough to mill aluminum if you do not go the polymer 80% lower route.

The cheapest drill press and router aren’t going to work well with aluminum 80% lowers and can burn them up pretty quickly. You also need a vise to hold the lower as you mill, and cutting fluid to make milling smoother and to preserve tooling. A shop vac makes removing the raw shavings easy as you mill.

When milling, you should always wear ear and eye protection as well as gloves and a long sleeve shirt. If you think bacon grease is hot, you’ve never felt hot bits of metal hit you.

Try It Out

There is nothing else like building your firearm. It’s challenging, but fun. And ultimately, it’s incredibly rewarding. The fun doesn’t end once the gun is built, either. Because once it’s done, you have the joy of shooting and owning the gun you made. That’s an awesome and uniquely American feeling.

About The Author

Almo Gregor is a firearm enthusiast, avid hunter and lifelong 2nd amendment supporter. Outdoors, hunting and shooting were a big part of his childhood and he continues with these traditions in his personal and professional life, passing the knowledge to others through freelance writing. He is also an editor for Outdoor Empire.


The author

Tyler Capobres has years of experience torture testing guns, knives and gear to their limit. If he's not writing about gun projects, reviewing products or mocking anti-gun zealots on Twitter, you'll find him at the range. Owner of thegoodgun.com, a website dedicated to all gun and knife enthusiasts. Author of "Punching Holes", a book showing how anyone can save 15-40% on guns, ammo, knives and more, by purchasing them at wholesale prices.

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