How to Complete an 80% Lower Receiver

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80% lower receiver how to complete guide
80% lower receiver how to complete guide

An AR 80% lower receiver is the part of the firearm that houses the bolt, firing, and mechanism. It is generally the “action” of a firearm. The partially completed lower receiver contains no fire control group pocket cut or any fire control group holes drilled so it is not legally a firearm. An 80% lower receiver is an unfinished lower or 80% complete, which means that no federal firearm license is required for purchase.

With an 80% lower jig and a handful of tools it’s never been easier to complete an 80% lower receiver. You can take pride in the fact that you just finished an 80% lower all on your own!

When completing your 80% AR lower receiver, be sure to take your time as you follow these simple instructions. There’s no need to rush the project. Pay extra attention to detail once the lower is completed.

Step One

Begin by acquiring the necessary tools to complete your 80% lower. Please refer to the list of recommended tools needed to complete your 80% AR lower receiver.

Recommended Tools:

  • 80% Lower Jig
  • 5/32” Drill Bit
  • 3/8” Drill Bit
  • 5/16” Drill Bit
  • 3/8” End Mill
  • Dremel with 1⁄4” Grinding Head
  • Drill Press Vise
  • Drill Press 

Now that you have all your tools, assemble the 80% lower jig side plates marked A & B and then install the Top Plate marked VA-C. Make sure the jig is “loosely” assembled at first. Once the jig is located properly on the rear take-down and sitting on the trigger well, the bolts can be tightened.

Top Plate C, clearly marked 1- 1⁄4” deep, is the profile to follow to make your cuts. It is 1- 1⁄4” deep from the material is touched so set the stop on the drill press accordingly when setting up your jig. To make it easier on yourself when switching to the end mill later on; we suggest starting with the 3/8” drill bit and drilling each radius corner in Top Plate C.

Remove as much material as possible after you finish drilling the radius. Do not overlap the holes as you drill as it will wear the drill, possibly break it, and make drilling process much more difficult. 

Step Two

Remove the “webs” created from the drilling process. Using the 3/8” end mill, open up the pocket fully by plunging it directly down on the webs. 

Create a flat bottom with the end mill. In a plunging motion, use the end mill until you have removed all the “webbing.” Drill points on the bottom of the receiver from the previous operation. The finished depth of the pocket the end mill should be 1-1/4-inches. 

Step Three

Remove the webbing and change Top Plate VA-C to Top Plate VA-D, and switch back to your 3/8” drill bit. Repeat Step 1 and Step 2 with plate VA-D. The depth is marked for this plate as well. Clear the web material using your 3/8” end mill just like in Step 2.

Step Four

Go ahead and take care of the trigger slot while the VA-D plate attached. Switch to the 5/16” drill and drill through the entire fire control group in the slot provided. Clean it up with a hand file or Dremel with a 1⁄4” head after completion. Watch for drill walk during this process and make sure to not overlap the holes.

Step Five

This step will focus on the side plates, A & B. This process is pretty straightforward. It’s NOT recommended that you drill all the way through. This may cause “walk” if the wall on the other side of the fire control group isn’t perfectly square. Turn the 80% Lower and 80% Jig on its side. There, you will see two trigger-pin holes, the 5/32”, and the safety selector hole, 3/8.” After you drill halfway through the lower from one side, flip the 80% lower over and repeat.

Step Six

You may now remove the jig and begin smoothing the internal profile with a Dremel tool or file. Reassemble the jig from time to time to check your finishing. You can leave the jig assembled for everything but the trigger slot, which will have to be done with the lower removed.

Congratulations! Under the Gun Control Act of 1968 you have just finished your own 80% lower receiver. If you are interested in obtaining your own kit to complete a project be sure to pick up your very own Ar 15 Rifle kit from Ormond Arms