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FAQ

How do I finish an 80% lower receiver?

You do not need to have any machining experience in order to finish our 80% lower receivers. All you need is a drill press, a few drills and end mills, and the 80% Arms Jig. You can view our step by step guide by clicking here.


Am I required to engrave a serial number onto my 80% lower receiver?

Per federal law, an individual building a firearm for personal use is not required to mark it with a serial number.

Some states may have more restrictive regulations. The following is for California residents ONLY: In July 2016, California passed AB 857 which requires all completed firearms to have a serial number applied by Jan 1, 2019. An 80% lower receiver is not a firearm, so a serial number would only be required once the 80% lower receiver is completed. Unfinished 80% lower receivers do not need a serial number.

If you build an 80% lower into a 100% lower receiver after July 1, 2018, you must FIRST apply to the California DOJ for a serial number, pay a fee, and they will then assign a serial number that you must apply to your firearm. If you built your firearm prior to July 2018 and already engraved a serial number of your choosing that is compliant with ATF regulations, the text of the law seems to indicate that this should be in compliance. However, we have heard that CA DOJ has made statements suggesting that people must engrave a new DOJ issued serial number on their lower even though the lower receiver already has a ATF compliant serial number engraved on it. In our personal opinion, it doesn't seem like this what AB 857 actually requires, however we are not lawyers and can't offer legal advice. Please do not reply on our opinion. We suggest you read the law yourself and come to your own conclusion. If you want to minimize your risk of encountering problems with the CA DOJ, it may be advisable to engrave a CA DOJ issued serial number.

If you build an 80% lower and do not use a DOJ issued serial number after July 2018, it is a misdemeanor. Getting a serial number for a lower in CA is not the same thing as registering it as an assault weapon. That is a whole different process.

80% Arms offers an 80% lower receiver serialization service. We have an FFL license and can engrave a serial number on your completed 80% lower receiver that meets ATF requirements.


Do you have an ATF determination letter?

Yes, we have received a letter from the ATF certifying that they do not consider our 80% lower a firearm. You can download a copy of this letter here.


Is this legal?

Yes, in our home state of California, as well as almost every other state in the U.S., it is legal to build your own firearm for personal use, as long as you can legally own a firearm. You must build the lower yourself; it is not legal for somebody else to do it for you.

From the ATF: 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 CFR 478.92 if it is sold or otherwise lawfully transferred in the future. 

Source: http://www.atf.gov/firearms/faq/firearms-technology.html


If I live in California, are completed 80% lowers subject to the CA Assault Weapons ban?
Do I need a bullet button?

Completed 80% lowers are subject to all the same laws that apply to any normal firearm. If you live in CA, you need to be careful to follow the laws related to the assault weapons ban. In general, if you build AR-15 style rifle with a pistol grip, you will need a device that prevents the removal of the magazine without disassembly of the action. A "bullet button" no longer counts to make the rifle California compliant. There are also "featureless" configurations that do not require a device to lock the magazine in place while the action is assembled. For more info on following CA laws, Calguns.net has a very helpful flowcart: http://www.calguns.net/caawid/flowchart.pdf 


What are ATF Requirements for Serializing a lower?

First, home built rifles for personal use are not required by federal law to have a serial number. However, some people wish to engrave one anyway, or you may be required to engrave one if you live in California (see above).

For firearms manufactured in the United States by a commercial firearms manufacturer, federal law requires the following information to be present:

  1. A serial number (must not duplicate another serial number you have used before)
  2. Caliber. Most people write “Caliber: Multi”.
  3. Manufacturer's name. Generally this would be your first and last name.
  4. Manufacturer’s city and state. This would be the city and state in which you live.
  5. (Optional) If you have decided to assign a model number to your 80% lower, you must engrave it onto the lower. If you have not elected to make up a model number, you do not have to engrave one. (In California, a model number is required to register a home built firearm as an "assault weapon.")

The above information must be engraved to a depth of .003 inches and the text size must be at least 0.125 inches high. 

80% Arms can assist you with engraving a serial number onto your complete or unfinished 80% lower that meets these requirements. We use a high powered laser engraver that will cleanly and precisely burn into any metal material.

Disclaimer: We are not lawyers. The above information is not intended to be legal advice. Please do your own research, consult a lawyer, and do not rely on the above information. Check your local laws and make sure to follow all of them.