80 Percent Lower Milling Instructions: A Guide by American Made Tactical

There are many ways to modify your firearm with components that optimize performance, change its overall appearance or both. At American Made Tactical, we specialize in producing cutting-edge 80% lower receivers, as well as lower jig kits for AR-10 and AR-15 rifles, to allow firearm enthusiasts the opportunity to build their rifles on their terms. Because the process can be complicated, 80 percent lower milling instructions are essential for novice gun owners or those new to modifications to ensure their AR-10 and AR-15 rifles are built properly. Fortunately, we can teach you exactly how to finish an 80 lower successfully so you’re ready to hit the shooting range right away. Let’s go over the instructions for using a tactical machining jig kit from our selection.

Machining is risky. American Made Tactical is NOT responsible for any broken end mills, drills, or failure. There are NO returns or refunds on any machined parts. Jigs do not come with tooling. To purchase, click here

Tools Required When Using a 80 Lower Tactical Machining Jig Kit

Before you start working with one of our tactical machining jig kits to finish an 80 lower receiver, you should know what tools will be necessary to complete the process. If you’re missing any equipment, you may have to wait to set up your 80 lower. 

If you want to know how to finish 80 lower components, here’s a rundown of the tools you’ll need: 

  • Hammer
  • Utility knife
  • Punch set
  • 80 lower drill press
  • Drill stop
  • Tooling kit
  • Aluminum cutting fluid
  • Shop vacuum or air compressor
  • Measurement tool

After you have these tools, you’re officially ready for our 80 percent lower milling instructions.

Step-by-Step 80 Percent Lower Milling Instructions

Now that we have everything, it’s time to dive into our 80 percent lower milling instructions. Please note that machining is very risky and requires patience and caution when using an 80 lower drill press, jig kit and all other tools.

Step 1: Setting Up Your Workspace

Before you begin, make sure you have your workspace completely tidy and ready. Otherwise, you may lose crucial components during the machining process.

  1. Unpack everything and lay it out on a flat surface. Please note: USE THE INCLUDED DRILL STOP FOR MORE ACCURATE RESULTS.
  2. Place the left and right side plates on the lower.
  3. Place the nest plate (center plate) attaching to the left and right plates with the set screws provided.
  4. Tighten down with the Allen wrench provided

Step 2: Milling Plate #1

  1. Set 1st plate (honeycomb style plate) into nest plate. Tighten down with the allen wrench and set screws that were provided.
  2. Drill .375 dia. Drill 2 inches deep from face of plate. Note: the drill stop is on to ensure correct depth. We recommend a digital measurement tool for extra accuracy, like the one pictured below, but another measurement tool, like a tape measure, will work.
  3. Also note: due to build-up of chips you will more than likely need to remove the plates to vacuum or blow out excess aluminum chips.

Step 3: Milling Plate #2

The next few steps involved in the 80 percent lower milling instructions will essentially follow the same procedure as your last step working with the first plate.

  1. Remove the first plate and replace it with the second plate.
  2. Use 3/8 dia. end mill to mill out #2 plate – 1.375 deep from face of plate. Use drill stop for better accuracy.
  3. When milling around plate, shaft of end mill is able to hit side, make sure it is low enough so it is not cutting the plates as you mill. Also note, take it a small layer at a time, do not plunge down to 1.375 right away or it will take you a very long time. Take it a bit at a time, or however much your drill press, mill, or drill can handle. Keep lubricated with aluminum cutting fluid for smoother cutting.

Step 4: Milling Plate #3

  1. Remove #2 plate, replace with #3 plate.
  2. Use a 3/8 dia. end mill to mill out the third plate 2.00 inches deep from the face of the plate. This step will take the longest, so don’t be afraid to take it in shifts! Again, take this one small layer at a time and don’t plunge down to 2.00 right away or it will take you a very long time to mill, especially if you are just using your 80 lower drill press. Once again, make sure your drill is lubricated with aluminum cutting fluid for smoother cutting.

Step 5: Milling Plate #4

  1. Remove #3 plate, replace with #4 plate.
  2. Use 5/16 dia. end mill to mill out #4 plate through the bottom of the lower. You will go completely through the bottom of the lower.

Step 6: Drill Through the Jig Kit and Lower

  1. Use 3/8 bit to drill through the hardened drill busing side of the jig kit and go through both walls.
  2. Use a 5/32 drill bit to drill through both remaining holes through the entire lower on hardened drill bushing side.

After you remove the plates and clean the lower, you’re officially ready to start your build!

Order Lower Jig Kits from American Made Tactical

Now that we’ve taught you how to finish an 80 lower, it’s time to order the parts you need. When it comes to firearm modification, the last thing you want is low-quality components that can tarnish your gun. That’s why we strive to manufacture the best 80 lower receivers with top-of-the-line jig kits. Browse our selection of products to get started, or contact us with any questions you may have. We look forward to working with you!