Building an AR-15? You've probably come across the terms “stripped lower receiver” and “80% lower.” It's important to know what these two things are before you start your build. You'll need one or the other to complete your rifle or pistol, so let's explain:
What is an AR-15 stripped lower receiver?
The AR-15 stripped lower receiver is the empty aluminum or polymer housing that holds the trigger, safety, lower parts kit, buffer system (buttstock, tube, spring, and buffer), and the magazine. Think of it as the foundation for the lower half of the rifle. Once assembled, the lower and upper receivers meet and attach with two removable pins, like shown below.
Important note: The stripped lower is the only part of the AR-15 that's legally considered a firearm. To buy one, you need to fill out the NICS paperwork at your local gun store or FFL for a background check, pay the appropriate fees to the government, and provide ID. This is no different than if you were buying a ready-to-fire rifle or handgun. Even though a stripped lower doesn't function without any parts installed (like a trigger), the law treats it no differently than a loaded up rifle with a 30-round magazine, hammer cocked.
What is an 80% lower receiver?
The 80% lower is a receiver blank, an unfinished AR-15 stripped lower receiver that you, the end user, finishes at home. It isn't legally considered a firearm because it can't have any parts installed until you cut and drill it with an 80% jig, a special gunsmithing tool that includes the necessary drill bits. The jig shows you where to cut and drill. Special guide plates and measurements do most of the work for you. You can learn more with our intro guide to jigs.
Since these receiver blanks aren't considered firearms, they aren't regulated by the Bureau of Alcohol, Tobacco, and Firearms (ATF). You can purchase an 80% lower right now and have it shipped directly to your front door, no special paperwork required. In the eyes of the law, it's no different than a raw chunk of forged or billet aluminum.
Compatibility & Types
Receiver blanks and 80% lowers are designed to be compatible with their weapon platforms' retail counterparts. For example, a cut and drilled AR-15 80% lower is identical to a store-bought AR-15 stripped lower receiver and they use the same components. We also wrote a guide comparing all available 80% lower receivers (calibers and platforms) to help you decide what to build. Currently, 80% lowers and receiver blanks exist for the following platforms:
"Is this legal?"
Yes. The Gun Control Act (GCA) of 1698 says you can legally build a gun at home from scratch, using a receiver blank. No paperwork, serial number, background check, taxes, or fees are required. The firearm in question must be for personal use. The ATF even backs all this up:
" No, a license is not required to make a firearm solely for personal use. However, a license is required to manufacture firearms for sale or distribution. The law prohibits a person from assembling a non–sporting semiautomatic rifle or shotgun from 10 or more imported parts, as well as firearms that cannot be detected by metal detectors or x–ray machines. In addition, the making of an NFA firearm requires a tax payment and advance approval by ATF." [18 U.S.C. 922(o), (p) and (r); 26 U.S.C. 5822; 27 CFR 478.39, 479.62 and 479.105]
Why AR-15 owners choose to buy a receiver blank
- They don't have to pay firearm taxes or fees.
- An 80% lower doesn't need a background check.
- They don't have to give up or register their information.
- They can buy everything they need online and it ships to them.
"How do I finish an 80% lower?"
This is a guide on how to complete an 80% lower receiver using a jig, and a router or drill press. Completing an 80% lower (or other receiver blank) with the appropriate tools will take between 30 minutes and 3 hours. Even if you’ve never machined metal, this project is pretty easy. Receiver blanks are designed so that amateur builders and the average gun owner can complete this project at home with some basic tools.
- 80% lower jig
- Drill bits (included)
- end mill bit (included)
- Handheld router
- Drill or drill press
- Tabletop or drill press vise
- Machining oil / cutting fluid
- Canned air and brush
- Ear and eye protection