AB 1621, AB 879 & AB 1057 Explained: California’s Precursor Part Rules

At Dirty Bird Guns and Ammo, we stay ahead of Sacramento’s regulations so our customers can build without running into trouble. Unfinished receivers, commonly called 80 percent lowers, are now fully regulated under three key bills: AB 879 (2019), AB 1057 (2021), and AB 1621 (2022). Every provision is active, with the final electronic approval requirement taking effect on July 1, 2025. All information here has been verified against the official California Legislative Information site, the DOJ Bureau of Firearms, and current FFL compliance guides.

Are 80 Percent Lowers Banned in California?

Eighty percent lowers are not banned in California. They remain legal if purchased through a licensed California vendor as federally regulated firearm precursor parts. Non-serialized or unregulated kits, however, are prohibited under AB 1621. You can still acquire compliant 80 percent lowers, but the process includes a background check, vendor transfer, and mandatory serialization once the build is complete.

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What Counts as a Precursor Part for an AR-15?

California Penal Code section 16531 defines a firearm precursor part as any unfinished frame or receiver that can be readily converted into the functional core of a firearm. For AR-15 projects, this means any 80 percent lower receiver, whether forged, billet, or polymer, designed to accept standard AR components. The DOJ provides a detailed guidebook with photos and measurements for identification. Complete uppers, barrels, handguards, and stocks do not fall under this category.

Do You Need a Background Check for Precursor Parts in California?

Yes. Every sale or transfer of a precursor part requires a Dealer Record of Sale (DROS) background check through a licensed precursor part vendor. The process mirrors firearm purchases:

• You must be 21 or older and legally eligible under California law.
• A processing fee of up to one dollar (adjusted for inflation) applies.
• Beginning July 1, 2025, all background checks must be submitted and approved electronically in real time.

California FFL Precursor Part Transfer Rules

Under AB 879, all California FFLs automatically qualify as precursor part vendors. The transfer process includes:

1. Customer presents valid government-issued photo ID.
2. Vendor submits the DROS eligibility check to the DOJ.
3. DOJ approves or denies the transfer.
4. Vendor records buyer information and retains records for five years.

Out-of-state shipments must be sent to the licensed vendor since direct home delivery is a misdemeanor. Dirty Bird handles this entire process in-house without third-party transfers.

How to Serialize an 80 Percent Lower in California

Serialization is mandatory under AB 1621.

• Apply for a unique serial number through the DOJ’s CFARS system at cfars.doj.ca.gov.
• Provide your name, address, and part details.
• The DOJ issues a serial number in the format of initials plus month and year plus a sequence number.
• Engrave it according to DOJ depth and placement specifications.

You must engrave and register before completing the machining process. Any unserialized build finished after January 1, 2024, is illegal. Pre-2024 unserialized builds required registration by that date to avoid felony penalties.

California DOJ Precursor Part Requirements

The DOJ enforces the following:

• Vendor licensing effective July 1, 2024
• Real-time electronic approval effective July 1, 2025
• Theft reporting within 48 hours
• Five-year record retention
• One-precursor-part-per-30-days limit effective January 1, 2024

Prohibited persons cannot possess precursor parts, and violation is a felony. Vendors must maintain a separate log for precursor part sales.

How to Comply with AB 879

Compliance is straightforward:

1. Buy only from a licensed precursor part vendor, which includes all FFLs.
2. Present valid ID and complete a background check.
3. Pay the processing fee and wait for DOJ approval.
4. For online orders, select transfer to a California vendor.

Dirty Bird processes these transfers quickly to ensure compliance with all regulations. Private-party or direct-mail transfers remain illegal.

California Build Kit Laws for AR-15

AR-15 build kits are legal only when the lower receiver is a compliant, serialized precursor part. Kits containing non-serialized lowers are banned. You can still purchase uppers, barrels, and accessories freely, but the lower must go through a licensed vendor with full DROS. Once assembled, the rifle must either be featureless or use a fixed magazine device such as an AR MAGLOCK to comply with Penal Code section 30515.

We Handle the Details

As a licensed precursor part vendor, Dirty Bird Guns and Ammo stocks compliant 80 percent lowers, runs on-site background checks, accepts out-of-state transfers, and assists with DOJ serialization. We handle every step so you can focus on your build. Visit, call, or message us and we will guide you through every requirement.

Official Resources

AB 879 Text: leginfo.legislature.ca.gov/faces/billNavClient.xhtml?bill_id=201920200AB879
AB 1057 Text: leginfo.legislature.ca.gov/faces/billNavClient.xhtml?bill_id=202120220AB1057
AB 1621 Text: leginfo.legislature.ca.gov/faces/billNavClient.xhtml?bill_id=202120220AB1621
DOJ Precursor Part Guide: oag.ca.gov/system/files/media/bof-reg-rev-fpp-id-guidebook.pdf
CFARS Serialization Portal: cfars.doj.ca.gov
DOJ Firearms Bureau: oag.ca.gov/firearms