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How to Complete an 80% Lower Receiver

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If you're wondering just how to complete an 80% lower receiver - it's never been easier. With 80% lower jig and a handful of tools you can take pride in the fact you finished your own 80% AR 15 lower receiver all on your own.

When completing your 80% AR lower receiver take your time and follow these simple instructions. There is no need to rush the project and you will be glad you paid additional attention to detail once the lower is completed.

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How to Complete An 80% Lower

Step 1:

The first step in completing your 80% lower is to acquire the necessary tools. The higher quality of drill bits and end mills you use will provide a more professional looking job. Below is a list of recommended tools you will need to complete your 80% AR lower receiver.

  • 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 

Begin by assembling the 80% lower jig side plates marked A & B. Next, install the Top Plate marked VA-C. Assemble the jig “loosely” then tighten all bolts once the jig is located properly on the rear take-down and sitting on the trigger well.

Top Plate C, is clearly marked 1- 1⁄4” deep. This is the profile you should follow to make your cuts. It is 1- 1⁄4” deep from the time you touch the material, so set the stop on the drill press accordingly when initially setting up your jig.

We suggest starting with the 3/8” drill bit and drilling each radius corner in Top Plate C. This will make it easier when switching to the end mill later on. Below is a picture of Top Plate C and the initial drill locations.

 

Once each radius corner is finished we can move on to the next portion of Step 1. After you have finished drilling the radius it is time to remove as much material as possible with the drill. Make sure you are not overlapping the holes as you drill. This will wear the drill (or possibly break it) and make for a much more difficult drilling process. See picture and suggestion below.

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Completing an 80 lower - step 1

Step 2:

The next step is to remove the “webs” that were created from the drilling process. Now use the 3/8” end mill and plunge directly down on the webs. This will open up the pocket fully. You will also be creating a flat bottom with the end mill. Use the end mill in a plunging motion until you have removed all the “webbing” and drill points on the bottom of the receiver from the previous operation. The depth of the end mill should also be 1-1/4-inches, which is the finished depth of the pocket.

Completing an 80 lower - step 2

Step 3:

Once the webbing is removed, change Top Plate VA-C to Top Plate VA-D, as well as switch back to your 3/8” drill bit. Repeat Step 1 and Step 2 with plate VA-D. You will notice this plate like VA-C, has the depth marked for you. Just as in Step 2 make sure you use your 3/8” end mill and clear the web material.

Completing an 80 lower - step 3

Step 4:

Since we have the VA-D plate attached, let’s go ahead and take care of the trigger slot. Switch to your 5/16” drill and drill through the entire fire control group in the slot provided. After completed, you can clean it up with a hand file or Dremel with a 1⁄4” head. Watch for drill walk during this process and do not overlap the holes.

Completing an 80 lower - step 1

Step 5:

This step will focus on the side plates, A & B. The Step 5 process is pretty straightforward. We DO NOT suggest you drill all the way through. Drilling all the way through may cause “walk” if the wall on the other side of the fire control group isn’t perfectly square. With the 80% Lower and 80% Jig on its side you will see the two trigger-pin holes, 5/32”, and your safety selector hole, 3/8”.

Drill halfway through the lower from one side, then flip the 80% lower over and repeat.

Completing an 80 lower - step 5

Step 6:

You can now remove the jig and begin smoothing the internal profile with a Dremel tool or file. You may want to reassemble the jig from time to time to check your finishing.

We recommend removing the lower to finish or accommodate more room to work. If you prefer, you can leave the jig assembled for everything but the trigger slot. You will have to do that portion with the lower removed.

Completing an 80 lower - step 6

Finished 80 percent lower receiver

Congratulations, you have just finished your own 80% lower receiver under the Gun Control Act of 1968. If you have further questions regarding the completing of your 80% AR lower receiver please contact 80-Lower.com for additional details.

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