More 80%
Now that you have the basics (if not HERE is part one) of what you will need to build and AR platform rifle from an 80% lower. We need to get into the meat of the project. First thing is to seclude yourself from anything else going on. You need your undivided attention if you want this to work. The next and most important thing is to follow the directions given to you with your jig. Make sure you have a solid platform to hold your jig, and that you have all of the tools you need. I can't emphasize this enough. The instructions came with the jig for a reason. All your measurements must be correct or you screw up the project and have to start over with a new receiver. Once you have the receiver in your jig and in the vice so it is solid. (That means no possible movement can happen. Again I say precision is essential.) You can begin the procedure of material removal. Almost all AR platform receivers are made of high-grade aluminum, with a milling bit, this should go fairly fast. I have made several and the time is about 3 hours. Your first one will take probably 4-5 hours. This will include setup time.
Now every jig is different. I prefer the jig sold by American Weapons Components. (formerly know as Ares Armor). The jigs they sell are very well suited for using milling bits. They do provide the information as to what size bits to use, and in what order to use them. Here is the link to the instructions for the Ares Armor jig. You will start by hogging out the material in the fire control group using a 3/8" end mill and plate number 1. Please pay close attention to the depth and don't try to take all the material out at one time, your cut with the first plate should be no more than 1.375 Depth from the top of the plate. That cut will give you the back ledge and the area to continue removing material with plate 2, your cut with plate number 2 will be made with the same 3/8" end mill, to a depth of 2.000 from the top of the plate. Now there is one more cut to make with the top plates. Plate number 3 uses a 5/16" end mill, this end mill is going to make a 2.250" cut, so you will need a 4" long end mill so you have the bit solid in the machine and long enough to make that depth of a cut. This cut is the last cut on the fire control group. you may need to go in and clean up the side walls, If you do so, do it carefully, very small amounts. Once you have completed milling out the fire control area, you will need to put the jig on its side so you can drill out the holes for the safety and the trigger and hammer pins. The hammer and trigger pin holes you will need a 0.156 diameter drill bit long enough to go all the way through the receiver. Now you have one last hole to drill, this one is for your safety. For this last hole, you will need a 0.376 diameter drill bit. Once you have this last hole drilled you are ready for the next step.
The rest of the build is easy in comparison. Now that you are all done with the cuts, clean any and all lubricants from the receiver and we begin test fitting. You will need to make sure the trigger and hammer will fit into the correct places and that all your holes are the correct size. Now that you have the information of how to machine out your receiver using a jig, it's time to make sure that you have all the other components of your build. This is where it gets fun. However, that brings me to part 3.
And there you have it straight from the gunsmith's mouth
U.S. Code 26 U.S.C. § 5842 "... anyone making a firearm shall identify each firearm, other than a destructive device, manufactured, imported, or made by a serial number which may not be readily removed, obliterated, or altered, the name of the manufacturer, importer, or maker, and such other identification as the Secretary [of the Treasury] may by regulations prescribe. (b) Firearms without serial number Any person who possesses a firearm, other than a destructive device, which does not bear the serial number and other information required by subsection (a) of this section shall identify the firearm with a serial number assigned by the Secretary and any other information the Secretary may by regulations prescribe. ===== 26 U.S.C. § 5871 — Penalties "Any person who violates or fails to comply with any provisions of this Chapter shall, upon conviction, be fined not more than $10,000, or be imprisoned not more than ten years, or both.
