What Is an 80 Percent Lower?
When you build an AR-15, you always start with the stripped lower receiver.
Why? Because, legally, it’s the regulated firearm component of the entire rifle or pistol. All the other parts you need to build an AR are not regulated, serialized, or controlled by the Bureau of Alcohol, Tobacco, and Firearms (ATF).
But even though the AR’s lower is considered the firearm, it can’t do anything by itself. It’s just an empty housing. It holds the trigger, hammer, safety, disconnector, and magazine. It attaches to the upper receiver — the part of the AR containing the barrel and bolt — and the buffer system, which manages the firearm’s semi-auto function.
So, if the AR’s stripped lower is legally the firearm, then what’s an 80% lower?
What’s an 80% lower?
An 80% lower is an unfinished stripped lower receiver. As sold, it isn’t machined to accept the fire control parts, so it can’t work as a receiver. Whether it’s legally a firearm depends on how complete it is. Under ATF’s 2022 frame or receiver rule, a receiver blank that can be “readily” completed, or one sold together with a jig or tooling to finish it, is treated as a firearm.
The Unfinished Parts of an 80% Lower
So, what parts of an 80 percent lower aren’t finished? These are the areas you must complete yourself, through drilling and fabrication, to make it a functional firearm:
- Drill the hammer pinhole
- Drill the trigger pinhole
- Drill the safety selector lever hole
- Machine the fire control group cavity
As the name implies, some areas of the 80% lower are already drilled and machined. Those parts include the:
- Bolt catch
- Pistol grip hole
- Magazine well
- Magazine release
- Buffer detent hole
- Trigger guard pinholes
- Upper receiver rear lug pocket
- Front and rear take-down holes
- Buffer tube threads and housing
Drilling the pin holes and finishing the cavity will make your 80% lower ready for assembly. You can purchase all the parts together in a lower parts kit and buffer tube kit.
The ATF’s Take on 80% Lowers
The ATF doesn’t use the term “80% lower.” It calls these parts receiver blanks. Under its 2022 rule (Final Rule 2021R-05F), which the Supreme Court upheld in Bondi v. VanDerStok in March 2025, a receiver blank that hasn’t reached the point where it can be readily completed into a working receiver is not a firearm, so it doesn’t need a serial number, an FFL or a background check. A blank that has reached that point, or one sold as a kit with a jig, is a firearm and must be serialized and transferred through an FFL. ATF and the Justice Department said in 2026 that a revised rule is coming, so check current guidance.
Types of 80% Lowers
The most common type of 80% lower receiver is made for the AR-15, like the forged and anodized lower pictured in this guide, up above. It is an unfinished version of the AR’s stripped lower receiver. These lowers work with 5.56 and .223 magazines and uppers, as well as some other calibers, like 300 Blackout and 6.5 Grendel.
Larger .308-type 80% lowers also exist for the AR-10 / LR-308 rifle platform, which can also chamber 6.5 Creedmoor. And lastly, 80% frames exist for certain handgun platforms, like the 1911, Sig P320, and GLOCK.
This guide compares all 80% lowers
This guide compares all 80% frames
Some states have banned 80% lowers
Receiver blanks aren’t legal everywhere. A growing number of states and cities restrict or ban the sale, possession or completion of 80% lowers and frames, and some, like California, require serialization and a background check. These laws change often, so check your state and local laws, and see our Shipping & Returns policy for the places we can’t ship to.
Frequent Questions
Q: Does an 80% lower need a serial number?
A: Under federal law, a firearm you make for your own personal use doesn’t need a serial number, though ATF recommends adding one so it can be traced if it’s lost or stolen. A receiver blank that ATF treats as a firearm (see above) must be serialized when it’s sold. Some states, like California, require serialization of homemade receivers and frames.
Q: Do I need to visit an FFL or fill out a Form 4473 to buy an 80% lower?
A: Not for a receiver blank that isn’t a firearm under federal rules. If a blank can be readily completed, or it’s sold as a kit with a jig, it’s a firearm and must be transferred through an FFL with a Form 4473 background check. Some states also require a background check for receiver blanks.
Q: Are 80% lowers legal under federal law?
A: Generally, yes, with limits. Federal law doesn’t prohibit making a firearm for your own personal use without a license, and receiver blanks that don’t meet the definition of a firearm can be sold like other parts. Blanks that can be readily completed, and kits sold with a jig, are regulated as firearms. Many states also restrict or ban 80% lowers, so check your state and local laws before you buy.
Q: Are 80% lowers different from factory-made receivers?
A: Once fabricated, an 80% lower is identical in form and function to its platform’s corresponding “retail-bought” receiver or frame. This ensures off-the-shelf components can be installed and the firearm can be customized with popular parts.
Q: What else do I need to assemble my receiver blank?
A: Receiver blanks are sold separately from the other parts required to fabricate a firearm. In addition to the lower parts kit and buffer system, you will need the upper components. Here’s a complete AR-15 parts guide. It covers all the required parts, and their compatibility, in detail.
This guide is general information, not legal advice. Federal rules for receiver blanks are changing, and state and local laws vary. Check current ATF guidance and your state’s laws before you buy or build.
