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80 Lower Guide | When Are Serial Numbers Necessary

Posted by Arthur Adler on May 12th 2023

80 lower builds gained popularity in the firearm world primarily because they were a way to get rifles and pistols without the need for registration. Buyers can order them online and complete their 80 lowers with many different tiers of tools. But for those who have just come into the 80 lower build scene, understanding why and when an 80 lower does not need a serial can be a fuzzy area. So here we are to clear up some of the fog about serial number’s and other regulations in relation to 80 lowers.


The Bureau of Alcohol Tobacco and Firearms (ATF) is the federal power that regulates firearms. According to ATF, the part of the rifle which controls shooting, or the fire control group, must be under 80% complete to not be considered a firearm. This gives birth to the name 80% lower, as the fire control group is in the lower receiver of the AR-15.

If the receiver is under 80% complete, then it cannot be under regulation under the ATF, meaning no serial numbers are required.

However, some states, like California and New Jersey have tried to crack down on 80% lowers. The Dept. of Justice of California has issued AB 857, a law that forces legal gun owners to register any lawfully unserialized firearm with a state issued serial number.

The best way to be sure about whether your rights are protected in the state you are in, is to research and take actions with a legal attorney.

The National Firearms Act prevents unserialized firearms from containing destructive or explosive ammo. If the firearm is fully automatic, the firearm must also be serialized.


Purchasing an 80 lower is all fine and good if you intend to keep it. However, if you plan to sell your 80 lower built firearm to someone else, you could be in violation of the law. 80 lowers are strictly prohibited from being bought with intent to sell. In a court, it is usually harder to justify selling or exchanging these firearms.

However, if you do wish to sell your rifle, or any rifle for that matter, do so with an attorney, and make sure it is registered. Any firearm that is made to sell must be registered according to the law.

Hopefully this gave some insight into the nature of serialization and registration in relation to 80 lower firearms. We at Thunder Tactical understand the importance of protecting individual rights.

We are dedicated to providing our customers, and all who fight fight to preserve their rights, with parts, guides, and information to help them in all their endeavors. And what trouble is there if you’re having fun doing it? Visit our website for more information, and premium store for the best parts around!