​How to Build An 80% Lower | 80 Percent Arms Guide thumbnail image

​How to Build An 80% Lower | 80 Percent Arms Guide

80 Percent Arms   |   Aug 12th 2020

*This article was updated on July 28th, 2021 to mention the ATF’s 2021R-05. Please comment against the anti-gunner agenda and stand in solidarity with us and the 2A community.

Per the Second Amendment of the U.S. Constitution, all American citizens have the right to keep and bear arms. But since this amendment was ratified in 1791, we’ve seen incremental steps of our rights being trampled in the form of increasing barriers to purchasing, selling and owning firearms throughout the country. That’s why the 80 percent industry has been experiencing such a huge boom in popularity and business as more people learn about their rights that are being disregarded by anti-gunner politicians.

It’s understandable why many are turning to 80 percent lowers because of your ability to build your own gun starting from an incomplete lower which can help save you time and money all while avoiding some legal hassle. But how do you complete an 80% lower? It’s the first question all newcomers to this hobby ask when attempting their first rifle build.

Do you need a jig for an 80% Lower Receiver?

Yes! It would not be possible to complete an 80 percent lower receiver without a jig. We are currently on our third iteration of the Easy Jig. You will not need a drill press but will need a jig router, end mills and drill bits to be used in conjunction with an 80% lower jig in order to mill out the lower receiver.

What Is An 80 Percent Lower Jig?

We here at 80% Arms have made it as easy as possible for you to do so with the Easy Jig® Gen3. With this 80 lower jig, you can complete 80 lowers from any manufacturer that makes AR-9, AR-10 and AR-15 lower receivers. Using this jig, builders can mill out 80 percent lower receivers’ trigger pockets, safety pins and fire selector holes with tight tolerances to perfectly fit with your selected upper receiver parts.

Are 80 Percent Lowers Worth it?

Yes! Take your 2nd Amendment right into your own hands by building a gun that the government doesn’t need to know about without any extra fees, taxes or 4473 Form. Building your own guns out of 80 percent lower receivers and frames also takes you to a higher level as a gun nerd. By the time you complete your first rifle or pistol build you’ll have graduated from being the average hobbyist or enthusiast and hopefully feel like a firearms artisan. Be proud of your rights, your build and the gun that you can truly call your own.

Are 80 Percent lower Illegal now?

As of now, the past ATF’s determination letter that ruled 80 percent lowers to not be considered as firearms is still in effect. However, that could soon change if the ATF’s 2021R-05 (proposed rule to redefine frames and receivers) passes which could potentially ban our lowers on a federal level. If you haven’t already please comment against this unconstitutional ruling! The comment period ends August 20, 2021.

Tools Needed To Complete An 80% Lower80% arms tool kit

This is our complete guide on how to complete 80 percent lower receivers. We’ll guide you in the process of finishing your first lower, list the required tools and if you have any further questions, reach out to our legendary customer service team for additional comments or concerns.

When getting ready to complete an 80% lower you’ll need these tools and supplies:

  • 80% lower(s)
  • 80% lower jig (Easy Jig Gen3)
  • Speed Mill (choose compatible end mill size per your router)
  • Vise
  • Cutting Fluid i.e. TAP Magic, WD-40
  • Shop Vacuum
  • Screwdriver Set
  • Allen Key Set
  • Eye Pro
  • Ear Pro
  • Gloves
  • Face Mask

How To Finish 80% Lowers: Complete Guideeasy jig gen 3 w/ 80% lower

Once you’ve prepared all the tools and hardware, buckle up, because this is going to take a good amount of time. Carefully follow these instructions to have the best results with your 80 lower(s):

Step 1: Mount Lower Receiver to 80 Lower Jig

Start by taking the top plate and mount the lower receiver to it. To do this you’ll need to install the front takedown pin block first with two jig screws. Grab the pin that is designated for your lower receiver’s caliber (shorter pin is AR15/AR9, longer pin is LR308/AR10) and with it, secure the receiver to the top plate.

Then, using the buffer plate adapter, connect the lower receiver’s buffer tube area to the other side of the top plate with another two jig screws. next, use the black buffer screw support to the lower receiver and make sure it’s tight. Do not overtighten any of the jig screws and periodically check on the buffer screw support to make sure it remains on right. Once the lower is secured, install the sidewalls appropriately with three jig screws each. You’ll know if you did it correctly if you can see the numbers 1, 2, and 3 when looking directly down at the top plate which are the guide pin areas for the router.

Step 2: Mount Router Adapter Plate To Router

How the router adapter plate is mounted to your router will depend on which brand and model of router you have. Please refer to the user manual of the Easy Jig® Gen 3 to see which configuration works best for you. Some larger routers may even require the large router base plate.

Step 3: Drill Pilot Hole

easy jig gen 3 drilling pilot hole out

Mount the pilot guide to the jig’s top plate with its two respective screws. They will be thinner and longer than the jig screws you’ve been using so far. Plate the jig on a vise and clamp it down correctly per the photo above and not sideways. If the sidewalls are clamped sideways they will be damaged and the lower receiver cannot be milled out in this way. Once secured, prep the hole with your choice of cutting fluid. Carefully take a 21/64” drill pit and power drill downwards into the lower to create a pilot hole. This will help guide you for the rest of the milling process. Remove the pilot hole guide when done drilling through.

Step 4: Start Milling Processmilling depth gauge easy jig gen 3

Make sure you have attached the correct Speed Mill size to your router by checking our router compatibility list. Double check that you are using the #1 set of guide pins on your router first. Set the router’s depth to be locked at the first hash mark and begin your first milling pass. Use your cutting fluid generously and between each pass. You’ll feel the router’s movement become smoother as you complete your first pass.

easy jig gen 3 milling process

As you finish a pass, go back to the tick marks and increase depth length and continue milling your next pass. Repeat this process until you finish each tick mark under the number 1 guide on the top plate. You’ll then need to change out the guide pins for the #2 set. Repeat previous milling steps. Once you’ve finished all the #2 hash mark passes, remove the guide pins on the router and replace with the #3 set. Repeat previous milling steps until all #3 column’s hash marks have been reached.

Step 5: Drill Out Fire Selector and Pin Holesdrilling out fire selector pin holes on easy jig gen 3

Place the jig on its side while still being clamped down in the vise with the right sidewall facing up. You’ll need two drill bits to drill out the fire selector and safety pin holes: 3/8” and 5/32”. Drill all the way through to the left sidewall. Once all three holes have been drilled through, congratulations! You’ve completed your lower into a 100% receiver!

Make it Easier With 80% Arms

80% arms raw ar10 lower completed

Do these instructions look confusing, or you just aren't sure what they mean? No Problem. We've made things easier than ever with the release of our Easy Jig® Gen 3! Check out the product page for videos of how simple it really is, or our instruction manual page to see how simple we have made all of our products. Also, don't forget, we offer the Foolproof Guarantee! If you happen to mess up one of our lowers with one of our jigs, we'll replace it at a 50% discount.