At the risk of sounding like a cheesy salesman, there’s probably never been a better time to build your own lower receiver. Because the conventional wisdom during the Presidential election did not favor Mr. Trump, AR manufacturers produced product by the truckload and now their inventory runneth over.
On Brownells website you can pick up an AR-15 80% lower for as little as $45 or a 308 lower for $109. (They also sell the James Madison Tactical 308 Lower, which is one of the products we’re reviewing in this piece, for $139 with a jig).
To me this seems like a once in a lifetime opportunity to build your own AR platform rifle at prices that aren’t going to get much lower.
Why build your own?
In my case, I didn’t own an AR 10 and this seemed like a good time to acquire one. In addition to saving money, the project seemed like a fun thing to do. In years past I’ve built stripped lowers, which is like building an erector set, but taking on an 80% lower takes it to another level. That said, it’s not all that difficult to do and there’s psychic value in shooting a firearm that you put sweat equity into. It’s also of course, a learning experience.
Our goal was to build both a polymer and a conventional AR 10 receiver and examine the differences in the finishing process.
The James Madison Tactical 80% Polymer AR 10 Lower
I became intrigued with building an .308 polymer lower after shooting one at a journalists’ event last year. I knew that polymer ARs have been controversial. Naysayers say they can’t hold up to the stress the way aluminum can. Proponents of the new technology of course differ. I’m not a materials scientist but logically if you can make polymer handguns, why shouldn’t you be able to manufacture a rifle with a polymer receiver?
Granted, there were production problems with some companies but nowadays folks that manufacture polymer receivers insist that these were growing pains.
What really appealed to me about polymer lowers was their light weight. The James Madison Tactical 308 polymer lower weighs in at about ½ lb vs. the aluminum lower from 5D Tactical, which tips the scales at about ¾ lb (finished).
JMT says it has developed its own hybrid polymers and fibers with additional reinforcements in high stress areas. The company states that its 80% lowers are engineered to Mil Spec tolerances from extremely durable fiber polymer materials and issues with corrosion, as could occur with aluminum .308 lowers, are diminished. The founders worked in the aerospace industry and were able to use their experience in advanced composites to design a lower receiver able to withstand the stress associated with firearms.
The lower we acquired is JMT’s “Gen 2” version with enhancements that include:
- Extended upper fire control box sections.
- Upper left magazine well box section.
- Webbed magazine wells on left and right sides (matched for MagPul) magazines.
- Extended bolt release roll pin posts.
The JMT Polymer 80 .308 80% lower is designed to Mil Spec tolerances for a high level of interchangeability with other Mil Spec .308 parts and accessories.
The lower comes as a kit with its own machining jig. The JMT jig has a 3-piece construction of plastic. It’s pretty basic compared to the 5D Tactical product but since all JMTs come with a jig you can toss it when you’re through.
The lower is well finished, looking a bit like anodized aluminum, and if you didn’t pick it up, you wouldn’t know the difference. It has a rough texture, more than you’d expect on a conventional lower, which I’m told provides better purchase when shooting.
To finish the JMT, essentially, you’ll need to machine a pocket for the Fire Control Group as well as drill holes for the Safety Selector, Trigger Pin and Hammer Pin. (That’s the same routine with the aluminum lower).
You can read quite a few positive reviews using the JMT jig but we decided to take a different route rather than using their system.
When preparing for the story we knew we were going to need a drill press and a “xy axis” vise. Scott Hanchette, the co-founder of JMT told us that we didn’t need an expensive vise but we couldn’t see buying a cheap one that we’d only use once.
I would suspect that a great number of people do not have a drill press in their home. So, we put ourselves into the position of an end-user who would really want to build a rifle but didn’t have access to a drill press.
What options does that person have?
Enter 5D Tactical.
5D Tactical Router Jig
My partner in this project (the guy who generally has better mechanical aptitude) was surfing the web and discovered Westborough, Massachusetts-based 5D Tactical whose entire raison d’être is to provide enthusiasts with a way to finish lowers without a drill press. The more I read, the more I liked the idea of jettisoning the drill press. However, you do need another tool to complete the job–a router. And not just any router. (More on that later).
We thought utilizing a router in this scenario was brilliant. (You can watch an overview of the product on this video). (There are two other companies that make “router jigs”—Modulus Arms and 80% Arms, also on the market).
The price point on the 5D Tactical Jig is $214.99, not cheap, but much less expensive than buying a decent drill press and vise. Of course, as I mentioned before, you’ll need the right router.
Andy Perry, the co-founder of the company was adamant that the best were the DeWalt DWP611, Porter Cable PCE 6435 or the Makita RT0701C. You’ll also need a hand drill, Allen wrenches, WD-40, a few C-clamps or a shop vise, screw driver, etc.
The kit comes with a top plate that has integrated depth gauges, two side plates, various pins, front take down and buffer adapter, release pins, a router adapter plate, drill guides, an adapter block and various screws.
In addition to the Jig you’ll also need several other items:
- (1) 3-Flute Hybrid End Mill
- (1) 3/8″ Black Oxide High Speed Steel Drill Bit
- (1) 5/16″ Black Oxide High Speed Drill Bit
- (1) 5/32″ Black Oxide High Speed Drill Bit
- (1) 3/8″ Drill Stop
Unless you have them, you’ll have to buy these separately for another $49.99.
Comparing prices, the JMT kit is less expensive and requires ordinary drill bits. (It’s a lot easier to drill into plastic).
The 5D Tactical set is of very high quality so you can use it ad infinitum. You can also build AR 15s with this jig but you’ll need to get their conversion kit for $114.99. (Likewise if you purchase their AR 15 jig you can convert it into a 308 jig with a conversion kit for $129.99).
Finishing the lower
The first step, as you might imagine, is to assemble the jig. This entails attaching the plates with the proper screws, pins and orienting them correctly.
Fortunately, it’s very straight forward to do so. What I really like about this system is that they provide excellent videos and written instructions with accompanying drawings that help the cause. Everyone takes in data in a different manner so if you don’t get the video, you’ll get the written instructions or vice versa.
As if the instructions aren’t enough there’s the dedicated 5D Tactical YouTube channel. This attention to detail is where 5D stands head and shoulders above most small companies.
Both the polymer unit from JMT and any conventional lower will fit the jig.
You’ll also need to attach the adapter on the router base. It should only take you 20-30 minutes to assemble the jig and adapter plate.
Part 2 of the process is of course milling out the receiver and drilling holes. (See the video which focuses on this endeavor). With the jig properly placed and leveled on a vise, you can get to work. Step one is to drill out a hole into the #2 guide hole. The first thing you’ll note, if you’re finishing an aluminum lower, are the sharp little chips flying everywhere. Best to wear a long sleeved shirt (my mistake) and of course safety glasses and hearing protection. Get your shop vacuum out, you will need it. After this step is complete you’ll need to do a similar pilot cavity in the #3 guide hole. You’ll want to be careful not to go too deep if there’s an integrated trigger guard.
From here on the milling of the Fire Control Group pocket begins. This is the longest task because you’re sequentially going deeper with each pass clearing out solid metal. During the operation you’ll need to squirt WD-40 into the cavity you’re creating to help cool things at the cutting face. The last operation in the milling process is to create the trigger slot—a very brief step.
The final task is to drill the holes for the safety and hammer/trigger pin holes on each side of the receiver.
The 5D Tactical billet lower which was a well finished, anodized affair and frankly indistinguishable from any other 80% lower. One advantage that this lower has, compared to other 80% lowers, is that they tap the hole where (previously) a conventional bolt catch pin was placed. Nowadays many manufacturers utilize a threaded bolt catch pin which is secured with an Allen head wrench. Thus if you want to swap out the bolt catch for some reason (maybe to add an “ambi” set up) you can easily do so.
It is priced at $109. They offer two more 80% models, a California compliant serial number engraved DPMS pattern AR-308 80% lower for $129 or a custom designed DPMS style AR-308/AR-10 80% lower for $149.99.
There were differences in milling out the two receivers as you might imagine. The JMT Polymer was incredibly easy to drill through and the plastic chips were pretty innocuous compared to the aluminum chips which seemed to settle in every crevice your body.
The whole process of setting up and finishing a receiver will take you anywhere from 1 ½ to two hours. It’s a fun couple of hours for sure—even with the aluminum detritus.
Overall I have to give five stars to the 5D Tactical Jig.
The set up and clamping system for the receiver was ingenious—they succeeded in engineering a system that maximizes stability of the receiver while minimizing the potential for minor scrapes and scuffs. Wreaking havoc is something I’m good at but the system is pretty much fool proof so long as you pay attention to operating the router and the proper steps in the process. I have to admit the royal we screwed up by not taking the longer release pin out of the jig when we started working on the JMT lower and managed to mangle it. Fortunately, we didn’t gouge the receiver in the process.
Live and learn.
I can unequivocally say that if you don’t have access to a drill press, you should seriously consider the 5D Tactical Jig system. If you’re interested in making more than one lower for your own use this kit will pay for itself quickly. Price for the jig and the necessary bits comes to $264.99 including the tools (and free shipping).
But do these lowers work?
Stay tuned! We’ll turn these stripped lowers into working firearms in the second part of this series.