How to Mill & Finish an 80% Lower thumbnail image

How to Mill & Finish an 80% Lower

80 Percent Arms   |   Nov 3rd 2022

Legal Disclaimer: The information in this blog is not legal advice. We are not lawyers. While we endeavor to keep all our blogs updated with the most accurate information, gun laws are ever changing and they can change quickly with little to complex differences in new legislation. Therefore, while we try our best to provide complete information, we acknowledge that everything you’re reading below may change (or already has changed).

Do not rely solely on the information provided by us or on this website for your purchase decisions. To ensure that you, the buyer, are acting in accordance with all federal, state laws and local ordinances, please be sure to do your own research and consult an attorney if necessary. 

It’s understandable why many are turning to 80 percent lowers because of the ability to build your own gun starting from an incomplete lower which can help save time and money all while avoiding some legal hassle. (Especially since we just got the legal injunction! 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.

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.

What is required to finish an 80% lower receiver?

So assuming you’re starting out with absolutely nothing, you should expect to be paying around $500 to $600 dollars for all the required tools, equipment and supplies needed to have a proper setup to machine your 80-lower and any future 80% lowers into a 100% firearm. The tools, equipment and supplies required include the following:

To save some money on tools you could try to look for second-hand tools being sold online on apps like Offer-Up or Facebook Marketplace. However, for specific tooling such as the 80 lower jig and the respective drill bits or end mill we recommend those to be new for the best results. For well equipped builders, you may want to use a drill press for the absolute best possible accuracy when drilling the safety selector and trigger group pin holes into the receiver.

If you’re working on an 80% pistol frame the only additional tools you’d need to add to complete your gun builder ensemble would be a dremel kit and a quality punch set made specifically for firearms. But of course, if you already have some of these tools then you’ll be pleased in being able to save even more money and get a new opportunity to use them as well.

Is it difficult to machine an 80% lower?

It can certainly be daunting to machine your first 80% lower receiver or frame. You might be worried about the mess, hurting yourself with power tools, or whether the holes you drill out will be perfectly straight — but don’t worry, it’s so much easier than it seems! We’ll go over all your potential concerns and provide you tips from our first hand experience and knowledge of having milled out several 80 lowers ourselves.

How to finish 80% lowers: Complete Guide

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):


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 over tighten 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.


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 HOLEdrilling pilot hole

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 lower on 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.

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 and pin holes

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!

Complete Your Next 80 Lower Build with 80% Armscompleted raw ar10 lower

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.