Ghost Story

I like the AR15 platform. Like many of my generation I was introduced to it by Uncle Sam, so I am intimately familiar with it’s operation and maintenance. I’ve owned a couple over the years. One I passed along because of financial need; self-employment is a fickle mistress. The other was a gun I assembled based on a .410 upper that proved to be just too problematic, and with a profound lack of foresight I sold off the lower I had assembled along with the .410 upper; A decision I have regretted several times since.

Since then I have thought of assembling another, but there was always a higher priority. The other week Linda finally got tired of me mentioning it and said, “just do it already,” so I started looking at lower receivers. You can get a well-made lower for well under $100; in fact the Aero Precision unit I was considering goes for about $60 locally. But then I came across something that intrigued me… A Tennessee Arms Hybrid 80 receiver, a polymer lower with metal inserts at stress points, with finishing jig for around the same price. Hmmm…

For those not in the know an ‘80% Receiver’ is simply not finished; generally the assembly-pin holes and space for the trigger mechanism are solid metal, making it ‘not a firearm.’ These can be transferred, sold, shipped through the mail etc. because it’s not a gun… yet. Basically anyone can get one, and with a certain minimum of tools and skill can turn it into a lower receiver (the essential part that ATF considers a gun.) Citizens of the US are allowed to make a gun for personal use, provided they comply with all federal and state laws regarding ownership of the specific type of weapon.

These have become quite popular with folks that don’t like the idea of the government knowing about their weapons, or to circumvent ill-considered or poorly written laws in some places. This has caused the media to create the term ‘Ghost Gun,’ referring to the fact that they are not tracked or registered, and there is an entirely spurious thought that criminals will be all over this idea. They aren’t; it’s far too easy to obtain weapons that are illegally imported or sold by the small minority of crooked gun dealers.

My interest was simply curiosity. How hard is it to finish one of these? I decided this would make a worthy project and went and bought one. Unfortunately I bought it from an aftermarket supplier; if I had bought it directly from Tennessee Arms it would have come with the appropriate drill bits and end-mill to finish it… and instructions. Mine didn’t. I looked it up online, and as you might guess it’s not rocket science. In the interest of seeing how hard it was with sub-optimum tools I decided to give it ago. Worst case I’d simply buy the Aero Precision lower I was intending to anyway.

Polymer lowers are often sneered at by the AR cognoscenti, but I checked and these have a good rep for reliability and durability. Since this is mainly a ‘fun gun’ that I won’t be running enormous amounts of ammo through I figure it will do, and as I said above, worst case I can buy a proper one. Anyway the polymer is much, much easier to work with than aluminum.

Don’t need to get into a serious tutorial here; there are plenty of those on Youtube. I’ll walk you though the process with photos.

Here’s the lower as it arrives, in the single-use polymer finishing template. Above it are the provided screws and nuts to clamp the jig over the receiver. The template is made from the same material as the part, and it’s quite a snug fit, which is good.
There are five tabs with pin-holes in them, and the first step is to drill these out to accept the screws. I used a 5/32″ bit for this.
After drilling I used needle-nose pliers to hold the nut while I installed the screws. These need to be very snug, but you don’t need to go nuts tightening them down.
here’s the top view, showing the area that will become the well for the trigger mechanism.
This is the part set up in my milling vice. This is a pretty fancy vise, but any simple 2-axis milling vice that is large enough will do. If you don’t have one a pair of strong hands on a stable base can manage it, but using the vice is a lot better. One big advantage of the jig is that it makes it very easy to clamp the irregularly-shaped receiver in place.
Here’s another view. I’m using a 5/16″ Cobalt bit, which is seriously overkill for this polymer, but it’s what I had on-hand.
The next step is to drill a series of holes in the space defined by the jig. These should be as close together as possible. The end result needs to be 1.22″ deep, but i decided to take it in stages, and initially had the drill press set for 1/2″ of penetration. It’s necessary to blow the debris from drilling out regularly to be able to see what you are doing.
Once the holes are drilled I began using the drill-bit to knock out the web between the holes. I used the vice to move the piece back and fourth while I gradually cut the webs down about 1/16″ at a time until I hit my 1.2″ depth.
After that I set the drill press for 1.21″ of depth. Rinse and repeat. The bottom was somewhat uneven, of course, so I took the drill bit to the belt grinder, sharpened it with a totally flat point and went back over everything, smoothing out the bottom and sides.
Now it was time to use the provided piece to locate and drill a hole for the trigger to pass through into the trigger-guard. The provided guide fits into the top of the jig. The instructions I saw said to use tape to hold it, but what the hell. It’s a single-use jig, so I just used a few drops of super-glue. I found a drill bit that fit the hole and drilled a hole in either end of the slot, then used the vise and bit to gnaw the web out between the holes.
The final step was to drill the hole for the safety and the trigger pins. The jig has the drill bit size clearly marked. There are two 5/32″ and one 3/8″ hole on each side. Do not drill all the way through from one side to the other! If the drill bit wanders it will ruin the part. Drill the holes part-way through from one side, them flip the jig and drill from the other.

I deliberately left a little extra material in the bottom of the trigger-mechanism well; it’s easier to remove material than to add it! When the trigger assembly arrives I’ll see if it works or if I need to go a hair deeper.

I did do some finishing work inside the well. Initially I used a sanding drum, but this wasn’t ideal. I wound up using a carbide bur to remove some of the roughness, and it’s looking pretty good.

This kit is bare-bones, and does not come with any of the lower receiver parts. I got a kit from Aero Precision for $27 with all of the pins. etc. needed. I was able to install the front assembly pin, the magazine release and bolt-stop, but the safety and rear assembly pin require the grip and stock to be mounted to secure them, so I’ll have to wait for those parts to arrive.

Here’s the finished lower… as finished as it can be before more parts arrive.

Once all the bits get we’ll talk what I’ve decided to build and why, and about assembling the gun… then we’ll see if it works!

Michael Tinker Pearce, 14 June 2020

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5 thoughts on “Ghost Story

  1. Doug McElwain

    I would love to try to build the AR-15 kit or the AK-47 kit and the 80% pistol kit. They’re more expensive than buying a new pistol but they aren’t traceable. The big problem for me is in every article I’ve read about building these kits they use a drill press. I don’t have one and don’t have access to one. That seems to make it hard or impossible for me to build one. Great idea though.

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