80% AR15 lower jig

thingiverse

This jig is made specifically for 80% lower receivers and it worked perfectly for my friend's Mil-Spec 80% lower as well as mine. I used this jig to mill out both lowers without any issues. Before you start, read the following: The Lower jig itself isn't designed for drilling holes, so I created a file called "Trigger Hole Template" which comes with two pieces. This template is attached to the lower using the rear takedown pin. Make sure the top edge of the template is flush with the top of the lower and mark the hole with a fine tip sharpie or mechanical pencil. Next, center punch the hole so the drill bit won't slip and then drill it out after milling. The 80 Depth Checker file is used to check for depth as well as making sure you're milling enough to the side. Mill it out until you can push the entire depth checker down. The oval cutout on the bottom of the depth checker is for the trigger hole, so trace it with a sharpie or something before drilling through. I used a harbor freight 1/2hp router and it was capable of milling out aluminum without any problems. To drill the holes, follow these steps: drill them last, use a 5/32" drill bit for the trigger and hammer, a 3/8" drill bit for the fire selector, and ideally you want the pins to go in tight. If it's too tight, use a fine file or 400-600 grit sandpaper wrapped around a toothpick/Q tip to slightly enlarge the hole. For milling depth, use the "Depth Checker" STL to check for depth and mark it with a sharpie before drilling out the trigger hole.