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Why Is It Legal To Build Your Own AR15?

Posted by on Apr 16th 2018

If you're new to the scene of DIY AR-15 building, you might be asking how it can be legal to build your own AR-15? The answer is relatively simple, so we'll do our best to explain.

All questions revolving around the legality of building an AR-15 begin at a federal law enforcement level. It is the federal government who defines and interprets what firearms are and are not legal to manufacture or possess within the United States. While states do have the right to pass additional legislation, the federal government is generally the deciding factor for most gun related laws.

Legal Oversight: The BATFE

The administration whose responsibility it is to investigate and prevent the unlawful manufacturing or possession of firearms is the Bureau of Alcohol, Tobacco, Firearms and Explosives (BATFE). The BAFTE also regulates the sale (through ATF Form 4473) and possession of firearms.

It is the BATFE who has provided the means by which an individual can assemble and build their own AR. The BATFE states: Individuals manufacturing sporting-type firearms for their own use need not hold Federal Firearms Licenses (FFLs). However, we suggest that the manufacturer at least identify the firearm with a serial number as a safeguard in the event that the firearm is lost or stolen. Also, the firearm should be identified as required in 27 CFR478.92 if it is sold or otherwise lawfully transferred in the future.

According to the BATFE the only part of the AR-15 recognized as a firearm is the lower receiver. And it is only the lower receiver of an AR-15 which the BATFE requires to be serialized by the manufacture. When purchasing a serialized lower, the purchaser is required to fill out a Federal Firearms License (FFL) transfer at the time of purchase.

Exception To The Rule

If you don't want a serialized lower or have to fill out an ATF Form 4473, the BATFE has made an exception for both serialization and the ATF Form 4473. This exception applies to the sale of an 80% lower receiver. According to the BATFE, an 80% lower does not meet the definition of a firearm, therefore, 80% lowers can be sold without serialization or an FFL transfer.

The term ‘80% lower' defines a lower receiver which is both incomplete and inoperable. The title, ""80% lower "" is designated because the lower is sold with the fire control group cavity remaining unmilled. Due to this lack of completion on the part of the manufacturer, 80% lowers do not meet the BATFE's legal definition of a firearm.

Building On An 80% Lower

While we do recommend you familiarize yourself with state and local laws, it is 100% legal in most states to both purchase and possess an 80% lower receiver. This also means it is legal for the purchaser to mill, drill and make the lower operable. The only restrictions are as follows: the purchaser (himself or herself) must complete the milling of the lower, the lower must be used for personal use, and the owner cannot not sell the lower receiver after completion.


Choosing to build on an 80% lower receiver offers a multitude of benefits. First, there is no FFL transfer and the lower can be shipped directly to your home. Second, you can experience the process of drilling and milling on your own. Third, no one but you will know you own the firearm.

For more info on completing your own 80% lower check out our helpful resources found here.

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DISCLAIMER: If you are new to the world of DIY gun building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. At, we are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.

We are a national retailer of individual components and not all products depicted on this website are legal in every state. Shipping of various products found on this website are prohibited to some states (such as California, Connecticut, District of Columbia, Hawaii, New Jersey, New York, Rhode Island, and Washington). The information, pictures, text or products presented on this website are not a representation by us, and should not be understood by you, that any product or completed firearm is legal to assemble or own in your state of residence. We encourage each and every builder to perform their own research about the state and federal laws that apply to them. It is your responsibility to understand the law and we encourage you to consult with an attorney or your local ATF representative.