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How to Complete an 80% Lower (and One Way You Legally Can’t)

You’ve probably browsed the 80 lower jig section and you may be wondering: Just how many ways can one complete an 80 percent lower? Can it be done without a jig? What tool options are at your disposal? Which way is truly best? If you’re new to this, stick around. We’re going through everything you need to know in this guide. Here’s how to complete an 80% lower – and one way you legally can’t.

How to Complete an 80% Lower

We’ll go over the two ways most builders complete their 80 percent lowers, but let’s first explain “how complete” an 80% lower is, and what you need to do to finish it:

A forged, black anodized 80 percent lower receiver used for building an AR-15.
A standard mil-spec, forged 80% lower. This is the most affordable and popular lower in use right now.

An 80% lower already has the following completed:

  1. Front and rear pivot pin holes are drilled.
  2. Front and rear pivot detent pin holes are drilled.
  3. Magazine release and catch slots are cut.
  4. Buffer housing is drilled and threaded.
  5. Buffer retainer hole is drilled.
  6. Pistol grip mounting area is cut and threaded.
  7. Magazine well is completed.
  8. Trigger guard holes are drilled.
  9. End plate mounting area is machined.
  10. Selector level detent hole is drilled.

An 80% lower needs the following operations completed:

  1. Mill out the fire control group area.
  2. Drill the selector lever hole.
  3. Cut the trigger slot.
  4. Drill the trigger pin hole.
  5. Drill the hammer pin hole.

Once you’ve completed these five steps, you’ll be the owner of a firearm. Finishing your lower creates an AR-15 stripped lower receiver that’s ready for assembly with a parts kit, buffer, and upper. Now, how do you complete these five steps?

Option 1: Use an 80 lower jig

The Easy Jig Gen 1 is pictured disassembled with its pins and bits illustrated.
This is the Easy Jig Gen 1, shown disassembled. The 80 lower jig is a simple tool that consists of a few plates, some drill bits and end mill bits, and pins.

Using an 80 lower jig is the standard way to complete an 80 percent lower. The 80 percent lower was designed so that shooters with no gunsmithing experience could easily build a black rifle (or pistol) from scratch. The key to making this project a success is making the required tools (the jig) easy to use.

Building a firearm at home would normally mean buying expensive equipment. So, the 80 lower jig was meant to be used with nothing more than a hand drill and a handheld router. These two common tools are the key to a simple, affordable project. But how does it work, exactly? Let’s take a look. Then, we’ll go over which jigs are available, and which one’s best for you based on your budget and needs.

How an 80 lower jig works

Easy Jig Gen 2 with 80 percent lower being secured - blog photo 1
The Easy Jig Gen 2 is pictured upside down, with a lower (protected by painter’s tape) being secured. Note the circled holes. These indicate where to drill. The red attachment is a shop vac fitting used for removing built-up metal shavings.

The 80 lower jig has two purposes:

First, it acts as a firearm template.

Two side plates and a top plate “sandwich” the 80 percent lower in place. Those plates have designated holes that create a “drill-here-and-here” template on the lower. There’s no measuring to be done. The jig determines where you’ll drill holes into your lower, and where you’ll remove metal using an end mill bit.

Each jig includes a set of bits. Most jigs come with three drill bits to drill through the lower (left) and one end mill bit to carve out the fire control group (right). You’ll use one of the provided drill bits to make a pilot hole in the fire control group.

Second, the 80 lower jig acts as a milling machine.

Once all your fire control group and pilot holes are drilled, you’ll be swapping out your electric drill and drill bits for a handheld router and the provided end mill bit. Most 80 lower jig plates include built-in depth measuring guides. These depth guides help you set the length, or cutting depth, of your end mill bit (pictured right).

 

 

Small notches in the depth guides indicate how many times you’ll adjust your bit’s depth until you reach the final depth. You’ll make about 3 to 4 cutting passes with the end mill bit before you make a depth adjustment.

This process mills out the fire control group, which is the final step in machining an 80 percent lower. Once completed, your lower can be assembled and made ready to fire using a lower parts kit and buffer assembly.

Types of 80 lower jigs

There are quite a few 80 lower jig options available, and each has its own pros and cons. Trying to compare every single jig would take hours, but we can give you a quick summary of the most popular options. The 80 lower jig is generally categorized into three types: Single-caliber, disposable, and multi-platform.

Single-Caliber jig: The Easy Jig

For builders who want to make a simple 5.56- or .223-chambered AR-15 and nothing else, the Easy Jig Gen 1 is the ticket. This single-caliber 80 lower jig is also one of the simplest in designs and it’s one of the most affordable, coming in under $200.

 

Multi-Platform: The Easy Jig Gen 2

The Easy Jig Gen 2 Multi-Platform builds on the simplicity of the Gen 1 with new features. It can complete pretty much any 80% lower, including AR9 and LR-308.

The Gen 2 is a nice upgrade because it only requires one pilot hole to be drilled for the fire control group. At around $300, the Gen 2 is also the most affordable multi-platform 80 lower jig you’ll find.

Disposable: The Polymer 80% Lower and Jig

Called the G150 Phoenix, this is a new lower-and-jig combination that recently hit the market. Designers and gunsmiths have successfully created a polymer 80% lower for the AR-15. This polymer lower affords an ultra-light design, weighing around 50% less than a billet or forged lower. If you’re building a lightweight carbine or ultra-light AR pistol, this is a great pick.

This lower includes its own disposable jig. The jig functions the same way any other 80 lower jig does except that it, too, is made of polymer. It doesn’t have any high-speed bearings or reinforced metal drill holes. In the process of machining your polymer lower, the jig usually takes some damage and is disposed of. This isn’t a concern because that’s how it’s meant to work. This combination is also around $75, making it incredibly affordable to just buy another one when you want to build another polymer gun.

Option 2: Use a drill press

The 80 lower jig basically acts like a drill press. If you were wondering: Yes, you can use an actual drill press to complete an 80% lower. This method requires knowing how to use professional machinery and calculating precise measurements. A drill press is not designed for milling, though basic machining can safely be done using one. This is the sort of experience only a craftsman or machinist usually possesses.

If you do have access to these tools, this is the least expensive way to complete an 80% lower. We also probably don’t need to tell you how to do it. Nonetheless, you’ll need schematics and measurements.

Ray Brandes, an expert machinist, wrote a very nice, detailed guide on how to complete an 80% lower using a drill press. Check it out here.

Someone else can’t finish your lower

Legally, you cannot allow another person or business to machine your 80% lower for you. Here’s what the ATF says, and why it’s illegal:

“Any person (including any corporation or other legal entity) engaged in the business of performing machining, molding, casting, forging, printing (additive manufacturing) or other manufacturing process to create a firearm frame or receiver, or to make a frame or receiver suitable for use as part of a “weapon … which will or is designed to or may readily be converted to expel a projectile by the action of an explosive,” i.e., a “firearm,” must be licensed as a manufacturer under the Gun Control Act of 1968 (GCA)”

To be clear, the above legalese doesn’t apply to you if you’re building your 80% lower for yourself. The ATF says you’re “engaged in the business of performing” if you:

“… devote time, attention, and labor to manufacturing firearms as a regular course of trade or business with the principal objective of livelihood and profit through the sale or distribution of the firearms manufactured.

Although having someone else finish your 80% lower may seem relatively safe (would be easy to not tell anyone), the legal ramifications are simply not worth the risk. The consequences for violating the Gun Control Act of 1968 could get you put in prison for many years. In fact, two separate individuals have already been indicted and convicted of illegal manufacturing. Each defendant received a sentences ranging from four to over six years.

Conclusion

We hope this how-to-machine-a-lower guide gave you all the info you need to build! We realize the 80 lower jig can still be a mysterious thing – there are plenty of options and features to consider. If you still have question about how to complete an 80 percent lower, just give a call or email us. Our customer team consists of a small group of AR-15 builders and owners. We’re here to help!

A quick recap:

  • An 80 lower jig is the easiest way to complete an 80% lower.
  • There are three types of jigs: single-caliber, disposable, and multi-platform.
  • Singler-caliber jigs are the easiest to use. Disposable jigs are the most affordable.
  • Multi-platform 80 lower jigs provide one solution for all types of 80% lowers.
  • You can complete an 80% lower with a drill press (and a little know-how).
  • No one else can legally finish your 80% lower for you.

DISCLAIMER: If you are new to the world of DIY gun building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. At 80Lower Jigs, we are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.

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