I have been wanting to build an AR from an 80% lower for quite some time, but the added cost of the jigs required for most of the 80% lowers on the market was a tough pill to swallow, especially since it could very well be one of those tools I would use once and then it would begin gathering dust. That all changed when I watched Jeff Zimba’s (the Bigshooterist) video of him building an EP Armory Kevlar reinforced polymer 80% lower.
That video made the task look ridiculously simple, and gave me the confidence to undertake it. At $75 a lower, I figured it was worth a shot. I must admit, I have a fairly well equipped shop that happens to include an upright milling machine, so I would have the added benefit of using that instead of a regular drill press, but even if I did not, I would still have undertaken this if for no reason other than the challenge of doing it myself.
Knowing that Christmas was approaching, and I wanted to add something extra for the wife under the tree (whether she wanted it or not), I decided to build her an AR all her own, and thus I ordered the pink lower. The wife type person is new to shooting, having gone through a handgun training class only a year ago, and while she enjoyed the class, she has been reluctant to try any of my rifles, so I figured having one built just for her might be the added nudge to get her to try it. Coincidentally, the pink lower made it much easier to see what was happening in the photographs I took.
The tools you will need to complete the machining will vary depending on which method you choose to use. I will be using my milling machine so I will need the proper end mill bits (3/8” and 5/16”), but others have completed the building using nothing more than a handheld drill and a rotary bit tool (Dremel tool) with a large bit, that is not so coincidentally sold by EP Armory on their website. While either method will work, I prefer the drill press/milling machine route because I do not trust myself to not destroy the lower with my Dremel tool.
No matter which route you choose to machine out the trigger pocket, you will also need a few drill bits to drill the trigger/hammer pin holes (5/32” drill bit) and the selector hole (3/8” drill bit). If you are going the Dremel tool route, you will also need a 5/16” drill bit to complete the slot for the trigger. If you are in need of the drill bits, those needed are available from EP Armory in a convenient “completion kit” that also includes the “bur monster” Dremel bit.
Additionally, I suggest a ¼”x28 tap as a needed tool, for tapping the pistol grip mounting screw hole, but some people say it can be done by forcing the screw in as it is turned. I feel better about actually cutting the threads with a tool designed for that, but that is a choice the builder is left to make on their own. Finally, a #42 drill bit can be useful.
The first task for me was to figure out how to clamp the lower into the vise so that it was not only level, but was also secure so that when I moved the table to begin the milling process, the receiver would not shift. I found that setting the trigger guard/pistol grip mounting area gave me enough surface area to securely hold the lower while also allowing me to adjust the level so that the machining process would produce a level bottom in the trigger pocket.
Once I had it mounted in the vice, and my 3/8” end mill bit was installed, I set about milling out the trigger pocket. First I took off the top part that was protruding from the receiver (black portion in the photo). Once the extra top portion was removed, I carefully lined up the bit to begin cutting down into the receiver. I dropped the bit into the work about ¼” at a time, and using the X/Y table controls on my milling machine, I moved the table in the appropriate direction and removed the black material, leaving just a sliver thin portion of it on the perimeter of the pocket. As you work your way down into the trigger pocket, pink colored bars (or whatever color your receiver is) begin to appear and extend from one side of the receiver to the other.
Side note: Those colored bars serve a dual purpose. They act as a guide for you as you machine the receiver and they prevent someone from being able to force out the black plastic to easily open the trigger pocket. Those bars actually necessitate the machining of the trigger pocket.
I continued this process, dropping a ¼” at a time, until I reached the bottom of the trigger pocket. You know you are nearing the bottom because the colored bars that extend through the trigger pocket will disappear leaving nothing but the black material. Once I had solid black, I slowly worked the bit down until I began to see the pink bottom of the trigger pocket and I made my final pass with the mill.
At this point, it was time to machine out the trigger slot in the bottom of the receiver, so I swapped out my 3/8” end mill for the 5/16” end mill. I had no instructions telling me how long the slot was supposed to be so I grabbed one of my AR’s out of the safe and measured it. It turns out that by using the 5/16” mill (or drill bit if you are using that method) and drilling a hole on either end of the black square protrusion, so that the hole just touches the black, provides you with the correct length trigger slot. In my case, I just used the mill bit to machine the slot, but if you are using the drill bit method, you will need to have a hand file available to clean up the slot.
Now that I had a place to drop the trigger through, I decided it was time to test fit the trigger (I was using a mil-spec DPMS lower receiver parts kit to complete this lower). I found that even though I had removed all but the thinnest sliver of the black material, I still had a pretty decent amount of material left to be removed (just a guestimate, but I would say almost 1/16” more to go). I used my calipers and measured the width of the trigger and using the calipers as my guide for the required width, I removed the additional material a little from both sides so that the trigger and hammer would be centered in the trigger pocket and so that both sides of the pocket would be equally thick (or thin).
The final machine work step necessary is drilling the holes for the pins and the safety selector. The holes are drilled from each side separately and both sides have a raised nipple that has a concave dimple in the top of it to locate the holes properly.
I chose to use the final drill size when completing this step, but in hindsight, I think using a smaller bit to drill a pilot hole would have been a wiser first step. While the nipples provided are useful in locating the starting point for the drill, as you drill down the nipple disappears and could (and in my case did) allow the drill bit to drift slightly making the holes not align perfectly. Drilling a small pilot hole first would have prevented that, and that is what I will do on any future EP lower builds.
Once the trigger pocket was fully hogged out and the holes are drilled, the assembly stage begins. Early in the assembly stage, I found another thing worth noting. While all the remaining spring and detent holes are already there, it is worth running a properly sized drill bit (by hand) through them just to make sure they are properly sized and free of obstructions. As I began to assemble this lower, I started with the front pivot pin and the associated spring and detent. While the spring dropped in freely, the detent actually got stuck and would not function properly. Removing the stuck detent was no simple task, but I managed it without damaging anything. Once removed, I ran a #42 drill bit in the hole by hand and reassembled it without any further issues.
As I previously mentioned, the drill bit wandered just slightly when drilling one of the holes, which happened to be one of the trigger pin holes. This became visibly apparent when installing the trigger. The trigger is very slightly cockeyed in the trigger pocket due to the misaligned holes. Not knowing how this might affect function, I continued with the assembly. Once all the trigger components were installed, I dry tested the trigger function extensively. Despite the slight alignment problems, the trigger functions fine. It is not nearly as clean as my other AR triggers, but it is functional none the less. That said, I will be keeping a close eye on the trigger/hammer interface to watch for any weird wear issues.
Once I had the lower parts kit installed, I continued with the assembly of the rifle and used the pink Magpul MOE furniture on the lower (unfortunately, the two pinks are different shades). As I planned on assembling a lightweight upper for her rifle, but did not yet have all the parts, I threw one of my uppers on her lower and put some pink Ergo brand rail covers on it so that it would somewhat match.
My wife, in addition to liking all things pink, is a girl raised in the ‘80s and as such, loves Hello Kitty. So, in addition to the pink parts, I located a Hello Kitty Punisher charging handle and had a custom engraved ejection port dust cover with Hello Kitty made. Come Christmas morning, she was actually excited to see her new rifle under the tree (if she was faking, she did a convincing job). Later Christmas morning, we took her new rifle out and shot it for the first time (I fired the first magazine through it just to make sure the trigger would continue to function properly). This was the first time she fired a rifle (other than a .22lr bolt gun) and it was amusing. She was totally safe and kept the rifle on target the entire time, but she was not used to the muzzle blast generated by a .223. After each round fired, she would let out a little scream, followed by a giggle. Her only complaint was that the gun was a little on the heavy side, and that will be addressed once the remainder of the parts for the new upper arrive.
The EP Armory 80% lower was not only a fun project to undertake, but it was also a challenge and rewarding. I have assembled AR’s before from stripped receivers and parts kits, but this is the first time I have actually manufactured a rifle. I can see this becoming a habit over the long run. If you have contemplated attempting a 80% lower in the past but were not sure if you could do it, this might be the lower for you. Right now, as I write this, the price for an EP Armory 80% lower is $65, which is $10 less than I paid. That is a hard price to pass up. In fact, I think I am going to go order another couple…
As always, your questions and comments are welcome.
Be safe out there,
Rifle Update: This morning, I finished assembling the new lightweight upper for the wife’s Christmas present. It consists of an Aero Precision upper receiver, a BCM mid-length gas system, 16″ lightweight barrel, a Yankee Hill free floated mid-length handguard with a low profile gas block. And, to top it off, a nice pink rifle sporting bits of Hello Kitty just would not be complete without a BattleComp 1.0!
Total weight of this gun (no optic or magazine) is 5lbs, 1.4oz according to my postal scale. It is crazy light weight!