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80% Lower Jig Instructions

Updated: 8/23/2020

What follows is the detailed process (one of many available) to finish your AR15 or AR10 80% Lower Receiver into a ready to use part.

TAKE YOUR TIME and be sure of each cut (check twice, cut once), and use the Drill Jig more as a “Point Guide” than a Jig and you will be able to use it several times if you like.  It is only intended to be used as an actual Drilling Jig just ONCE.

LEGAL – We’re pretty sure that everybody knows this already but we have to make the statement that if you choose to finish your 80% Lower into a functioning Rifle part, but FIRST check with your state and local laws to make sure that it is legal to do so.  Of course IT IS from a Federal Law standpoint as well as our 2A but the local governments can also be a serious road block to happiness.

Tools that you will need:

Besides the following list of Drills and Mills which is available as our standard Tool Kit, you would be best served to use a free-standing Drill Press to complete your Lower.  Hand held drills DO NOT work very well at all although there are customers who have reported using one.

  • 3/8″ Drill Bit
  • 5/32″ Drill Bit
  • 1/8″ Drill Bit
  • 1/4″ Std Length End Mill

Each instruction spelled out below corresponds to the image just above it.  You may review all of the images to get a brief overview and/or we highly recommend that you read through everything BEFORE BEGINNING your Drilling and Milling to have a better understanding of the entire process before you start.

 

80 percent lower AR-15-Drill Jig Instructions

 

STEP 1 – First align either Side Plate to your 80% Lower and insert (2) 1-3/4″ long allen head screws through to fasten all three pieces together – DO NOT tighten yet.

 

80 percent lower AR-15-Drill Jig Instructions

 

STEP 2 – Then attach the Drilling Top Plate and use (2) short 10-24 allen head screws to secure the plate leaving bolts loose once again.  Place the jig assembly on flat surface (Drill Press Table) standing upright and make sure everything is square and true.  Tighten all fasteners starting with Side Plate screws.

 

80 percent lower AR-15-Drill Jig Instructions

 

STEP 3 – Place the jig assembly on its side (Side Plate screw heads UP), and use the 3/8″ Drill Bit to drill the Selector Switch hole.

NOTE – You can drill the Selector Hole through, or just start the hole in the side of the Lower and go back later to finish.  We recommend to drill each side separately by flipping the Drill Jig assembly over to the opposite side.

 

80 percent lower AR-15-Drill Jig Instructions

 

STEP 4 – Next, use the 5/32″ Drill Bit to drill both the Hammer Pin Hole and Trigger Hole.  Once again, you can either drill through or just “start” those holes, and drill from both sides later.

 

80 percent lower AR-15-Drill Jig Instructions

 

STEP 5 – With the jig assembly standing upright, start drilling with the 5/32″ Drill Bit at every hole shown above as Green.  You can either “start” each hole, and then drill to depth after removing the Top Plate.  Or use the Drill Jig to drill each 5/32″ hole to a little higher than finished depth for the FCG main pocket of 1.250″.

 

80 percent lower AR-15-Drill Jig Instructions

 

STEP 6 – Continuing with the jig assembly standing upright, start drilling with the 1/8″ Drill Bit at every hole shown above as Orange.  You can either “start” each hole, and then to drill to depth after removing the Top Plate.  Or use the Drill Jig to drill each 1/8″ Hole to a little higher than finished depth for the FCG main pocket at 1.250″.

 

80 percent lower AR-15-Drill Jig Instructions

 

Progress Check – when you remove the Drilling Top Plate, your 80% Lower should look like the image above.

 

80 percent lower AR-15-Drill Jig Instructions

 

STEP 7 – Continuing with the jig assembly standing upright and the Drilling Top Plate removed.  Start drilling with the 3/8″ Drill Bit at every 1/8″ hole shown above as Blue.  Use the Drill Press to drill each 3/8″ Hole to a little above finished depth for the FCG main pocket at 1.250″.

 

80 percent lower AR-15-Drill Jig Instructions

 

Progress Check – when you are done drilling the correct number of 3/8″ holes, your 80% Lower should look like the image above.

 

80 percent lower AR-15-Drill Jig Instructions

 

STEP 8 – Attach the Milling Top Plate (as shown above) and continue with the jig assembly standing upright.  Use the 1/4″ End Mill at a mid-range RPM and do your incremental down steps at about 1/8″.  When you press the End Mill down (plunge) into the 80% Lower material, GO SLOW.  Then slowly trace around the outside perimeter of the smaller slot in the Milling Top Plate MAKING SURE that you have some “shank” (non-cutting surface) of the End Mill ALWAYS running against the slot walls.

NOTE – Be very careful NOT to go too deep.  You’ll want your finished depth of the FCG pocket to be 1.250″.

 

80 percent lower AR-15-Drill Jig Instructions

 

Progress Check – when you remove the Milling Top Plate, your 80% Lower should look like the image above.

 

80 percent lower AR-15-Drill Jig Instructions

 

STEP 9 (Optional) – Reattach the Milling Top Plate (as shown above) and continue with the jig assembly standing upright.  Use the 3/8″ End Mill at a mid-range RPM and start milling the small section between the FCG main pocket and upper Lug pocket going to a total depth of 0.630″.  Set your down steps to about 1/8″ and when you press the End Mill down (plunge) into the 80% Lower material, GO SLOW.  Then slowly trace around the outside perimeter of the smaller slot in the Milling Top Plate MAKING SURE that you have some “shank” (non-cutting surface)of the End Mill ALWAYS running against the slot walls – Remove the Milling Top Plate.

 

80 percent lower AR-15-Drill Jig Instructions

 

STEP 10 – Attach the Drilling Top Plate (as shown above) squaring and leveling once again to continue with the jig assembly standing upright.  Use the 1/4″ End Mill and SLOWLY press (plunge) the end mill thru the bottom of the FCG pocket.  There is only about 0.070″ of material to cut so you can just mill all the way through to the Trigger Guard area.  Use the 1/4″ End Mill at a mid-range RPM and then slowly trace around the outside perimeter of the small slot in the Drilling Top Plate – Remove the Drilling Top Plate.

 

Completion – when you are done remove the Slotting Top Plate and your 80% Lower should look like the image above which is a 100% complete and ready to use Lower Receiver.