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Finishing An 80 Lower Firearm - The Steps You Should Take

Posted by Jordan Vinroe on Dec 30, 2019

Finishing an  80 lower receiver can be simple if you take your time, pay attention to detail, and follow some basic instructions. With an 80% lower jig and some tools, you can give yourself great satisfaction by finishing your own 80% lower receiver into a customized firearm.

Choosing An 80% Lower Receiver To Finish

When looking for an 80% lower receiver to complete, there is a plethora to choose from. They’re made by many different manufacturers and out of multiple different materials. Your choice should be based on personal preference.

You can get an 80% lower receiver  delivered to your doorstep without ever having to complete complicated firearms paperwork because it is 20% shy of being considered a firearm. Typically, the main fire control group will need to be milled, along with a few other modifications, when finishing your 80 lower receivers.

Upper Assembly & Lower Jig

A complete upper assembly consists of:

  • Barrel
  • Bolt carrier group
  • Fore-end
  • Upper receiver

You can buy an upper assembly complete (nothing needs to be finished), ready to attach to a lower, or you can assemble one yourself.

A lower jig is a tool or device that shows you exactly where to mill out your 80% lower receiver. The built-in guides are positioned for precise milling and drilling. Depending on the type of receiver you use and how you go about completing it, the jig may vary.

Gather Your Supplies

Tools and workbench for finishing 80 lower receiver

Each gun that you build will require different tools for finishing an 80 lower. You should closely follow the instructions included with your kit or the parts you purchased to make sure that you are using the correct sizes and types of tools. While the sizes may vary, you’ll need a drill press and press vise, drill bits in various sizes, an end mill, and a Dremel for precise finishing work.

Drill Your Materials

To properly assemble your gun, you’ll need to first put your jig together and then drill your materials with the help of the jig. Each kit will have instructions that include the specific steps required to create the jig. From there, you’ll need to follow the instructions for drilling. Kits typically come with a template to show you exactly where you need to drill.

Finish Your Gun

There will be different steps you need to take depending on the 80 lower that you’ve purchased, but you’ll usually need to do some finishing work to it after you’ve drilled all the holes. Be careful when using a Dremel to clean the holes up because if it slips or bounces, it could change the shape of the holes. Precision is not only a necessary requirement of finishing an 80 lower, it’s critical.


Depending on what kit you’ve purchased, there will be specific steps for assembling your gun. It is important that you use the exact instructions that come with your kit. Even guns that are very similar could have instructions with a wide variance. Proper assembly is crucial when you’re putting a gun together since placing a piece even a few centimeters off can ruin the entire operation and function. As long as you’ve followed the directions for milling and you’re familiar with the way the gun operates, finishing an 80 lower is as simple as putting it all together!

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A Word Of Advice

DIY gun builds are not for beginners. You should have some knowledge of firearms, how they work, and make sure you always purchase from a  reputable supplier. Stay up-to-date on all federal, state, and local laws concerning buying, owning and building guns in your area to make sure that you are within legal limits. Laws are constantly changing especially at the state and local levels so keep that in mind when you’re doing your DIY build. When finishing an 80 lower receiver, mistakes may prove to be dangerous, or fatal, so if you have any questions about the process, ask a professional.