We began this series by finishing two AR 10 80% receiver lowers – one a polymer from James Madison Tactical and the other a an aluminum billet model from 5D Tactical. We completed them both with an elegant solution–a jig from 5D Tactical and a $125 DeWalt router.
It was relatively painless and, fun to do. It took us about three hours to do the whole procedure.
Our next step was to complete the build-out of the lowers with parts kits, buffer tubes, buttstocks, grips, etc.
Although I was reasonably sure we did a good job with our jig and router, there was a niggling feeling in the back of my mind that, maybe the alignment was off and the parts might not fit.
Yes, gun writers have plenty of insecurities. OK, well, I’m getting ahead of myself…
Assembling the James Madison Tactical lower receiver
The JMT unit is manufactured with hybrid polymer/composite materials (as the website explains). The main advantage I can see is its incredibly light weight. It’s nearly a quarter pound lighter than the aluminum lower from 5D Tactical. Finishing the JMT lower with the jig/router was a breeze because the material was so easy to cut through. After all, plastic is a helluva lot easy to mill or drill than metal. It also doesn’t generate those nasty little bits of aluminum that seem to want to enter every crevice of your body.
In a “normal” environment, the other advantage, would be price. Polymer is less expensive to manufacture but given the current glut of AR parts on the market (which will of course change someday) prices for aluminum lowers are very competitive with polymer.
Assembling or installing the LPK was straightforward. If you’ve ever put a stripped AR 15 lower together, this is the same drill. Most of the lower parts kit fit with no hassle but there were a few exceptions.
The only “issue” we had, and it was comparatively minor, was the addition of the bolt catch “assembly”. On the JMT the little slot was simply not wide enough to accommodate the catch. Thus we had to widen it. I rummaged through my tool box in order find a file that was thin enough to work. Alas I couldn’t find a thing until I remembered I had several 70 year old German pocket knives from my father which sure enough had files on them. It took a while but that did the trick.
I mentioned the bolt catch scenario to Scott Hanchette, co-owner of JMT, and he said that mag catches, although theoretically “Mil Spec” actually may vary in size from manufacturer to manufacturer. Thus the issue may have been an oversized catch as opposed to an undersized channel.
The second minor issue was placing the proper roll pin through the catch.
Nowadays on aluminum receivers the pin is threaded so instead of tapping it in, you screw it in with a tiny hex key. However, polymer lowers aren’t threaded. The LPKs we had from CMMG and XTREME Precision had the newer threaded screw catches. Thankfully, XTREME sent me some old fashioned pins and we were able to complete the JMT project.
Many shooters prefer to upgrade from a Mil Spec trigger and we were no exception. So instead of installing the stock fire control group that came with the stock CMMG LPK, we went with a brand new product called the Saber, which also happens to be manufactured by JMT.
Instead of the standard 6 lb pull, which is pretty typical of Mil Spec, a drop-in will take you to a whole other level of trigger-dom. With a good trigger, even if you’re not the world’s best shot, you’ll at least have the opportunity leverage every bit of “native” accuracy that your gun offers. Without a good trigger, you’re simply handicapping yourself.
Like other drop-in triggers, the Saber is a one piece unit that is oh-so-easy to mount. This one has a nice crisp break between 3.5 and 4 pounds.
The Saber has a very clean, precision machined sort of aesthetic that is very attractive. The trigger itself has a curved, rounded surface that feels ergonomically “correct”.
It’s simple to install, just pop it in, and add the safety latch. The unit is secured by four anti-rotation screws that lock down the trigger pins on either side of the receiver as well as two set screws on either side of the trigger, on the base of the housing. Those anti-rotation screws go a long way to stabilize the trigger on this polymer lower. Note (as we discovered) once you install them and add a little Loctite, they are in for good.
The other very attractive attribute its under $100 price point. Many drop in triggers are easily double the price. Hanchette of JMT said he’s able to keep the unit price low because he keeps his overhead very low.
One note of caution on the install: Do not over-tighten the set screws (which is what the documentation warns). When the set screws begin to encounter resistance, stop tightening. Given that this is a polymer lower, over-tightening will cause the bottom of the receiver to “bulge” where the screws come into contact with the bottom of the receiver. I would highly recommend that you either fabricate, or better yet, acquire a plate from a trigger manufacturer to place on the bottom of the receiver prior to trigger installation. This will ensure that you don’t mar the receiver by over-tightening the set screws. (Obviously this only applies to a polymer receiver).
Timney has an excellent little plate (see photo above) that they offer with their triggers that can be used for a polymer receiver.
CMMG provides the infrastructure
CMMG is a family owned company out of Boonville, MO and a long time manufacturer of AR-15 Rifles, .22LR AR-15 Conversion Kits and Accessories. They provided the LPK parts as well as buffer tubes, barrel nuts, springs and the like for this build. I went to CMMG because as the owner of CMMG AR 15, I’ve been very impressed with their products, their support and their quality for a long time.
Of late, the company has started to innovate with some variations on the AR 15 and AR 10 platform. These include the GURPRO series (chambered in .45 ACP) and their Mutant MK47, an AR style rifle, chambered in 7.62 x 39, that is a sort of cross between an AR and an AK. The new products have received kudos from firearms journalists. As the author of a book on the AK, I’m particularly intrigued with the Mutant.
Putting together the billet 5D Tactical Lower
At the risk of sounding smug, I was really pleased with the job we did finishing this exquisite lower. It is a CNC machined 7075-T6 billet featuring a “classic” DPMS Generation 1 compatible design. The anodized finishing job is superb. The price for this is a mere $109.
So what’s the difference between a billet and the more standard forged process?
A billet lower receiver is shaped from a solid block of aluminum, referred to as ‘bar stock.’ This ‘bar stock’ is formed from extruded aluminum. “Extruded” means the metal was formed into a particular shape by squeezing between two rollers. (Think of rolling a piece of dough.) From a piece of this extrusion or ‘bar stock’ a CNC machine then cuts the billet into the shape of the lower receiver, or in this case an 80% lower receiver.
Forged aluminum means that the metal has been ‘forged’ or “hammered” into a forging die to shape the aluminum to the desired shape and size. After the aluminum lower is forged into the initial shape, the piece is then ‘finished’ on a CNC machine.
So what are the differences between the processes?
A forged piece of aluminum is stronger (and lighter) than billet. The billet lower receivers are considered more aesthetically pleasing and are more expensive that forged receivers. As a matter of function, there’s no difference. Ultimately, it’s a matter of aesthetics.
Assembling this lower was a snap. The 5D Tactical the bolt catch pin is threaded so all you needed is a hex key to secure the bolt catch.
Adding the rear take down pin takes slightly more effort than a typical assembly. Normally you’d simply insert the detent and the detent spring in the cavity at the rear of the lower receiver. However the channel that accepts the spring and detent is longer than you might think.
In addition to a spring and detent pin you’ll need a 1/2″ long 4-48 set screw to plug the end of the channel and add sufficient tension to the take down pin. Another option is to cut a second detent spring in half and/or add a another detent and insert that into the channel as well. (You can forego the set screw altogether with this option). Another thing you may need to do is polish the business end of the detent that interfaces with the take down pin with the some emery cloth. Otherwise the channel in the take down pin may not slide smoothly and you’ll have trouble moving back and forth.
You can then seal things up with the receiver end plate.
For this pretty billet lower we acquired a top of the line Timney AR 10 Competition Trigger. I have used Timney triggers on my AR 15 builds and love them. Timney does one thing and one thing well—they manufacture single stage, drop-in style triggers. To be precise they produce over 20 different styles of triggers for roughly 100 models of rifles ranging from AR platform rifles and SCARS to Winchester bolt action rifles. They are hand–assembled, custom calibrated and all have life time warranties. You’ll drop at least $225 for one of these bronze babies but you get what you pay for.
Customer Service Manager Kevin “T-Bone” Dee once told me that one thing that really differentiates the Timney from its competitors is that each and every trigger is hand tested and hand calibrated on an action. The manufacturing process is also different from other companies. Timney uses EDM technology–a very precise way of manufacturing parts which erodes the metal (by running current through a wire) instead of physically cutting it. The critical parts–the sear, trigger, hammer are made this way. The upshot is that you can make incredibly precise cuts accurate to 50/100,000 of an inch or less.
What about maintenance? Don’t worry about lubing. Timney uses a Telflon nickel coating which doesn’t require oil. The main thing is to keep it clean. I clean my Timney on my AR with Hoppes #9 or a similar solvent and then blow the fluid out with compressed air.
Installation was easy. The trigger slid perfectly into the fire control group cavity.
After that it was just a matter of lining up the pins on either side of the receiver to install it. (Thankfully we drilled holes to the proper specs). We then added the safety, which also fit properly. The Timney also utilized set screws to help buttress the unit to the bottom of the cavity. You cinch the screws down with a hex key (provided by Timney). The challenge is getting them seated. You’ll need to move the spring’s prong which partially covers the opening that you’re trying to place the screw in. In order to do this you may need a screw driver or a probe to move the prong away and then finesse the screw in its proper place.
LPK from XTREME Precision
We used mostly XTREME Precision LPK parts on the 5D Tactical build. XTREME occupies the high end of the LPK spectrum. As owner Dave Cannon describes it they are an OEM manufacturer of “small parts for the AR platform” . They also make items such as compensators for the AR. (We’ll test one in a future story).
They will also sell direct to consumers over the web. Their own all new Swiss-made CNC machines, the oldest being only 4 years old. Their line of products target end-users who do a lot of building AR platform rifles and know exactly what they want. Their parts are a little more expensive but as usual, you-get-what-you-pay-for.
They also offer some pretty cool semi-custom options. For example we chose to use their DPMS Extended Take Down Pin set which includes an assembly tool for this procedure. The assembly tool is one of these specialty parts that you only need once in a blue moon and if you don’t have it, it’s a real pain to install the pin. Thus, it’s a thoughtful touch to include it.
What I really like about their kits is that they offer duplicates of detents, springs, etc. The little stuff that seems to disappear into the great void when you least expect. It’s nice to have duplicates of parts which can then also be used for future builds.
(You can get a 10% discount when purchasing directly from the Xtreme Precision website by using a “promo10%off” discount code when buying).
We didn’t skimp on the furniture. First and foremost was the Bill Rogers “Super-Stoc“, an item I’ve used on other builds. (I even have one on one of my AKs).
The Super-Stoc may not be as well known as products from Magpul or other brands but that shouldn’t stop you from giving it consideration. It’s strong, lightweight (7.3 oz) and its “Cam-Lock” system works great to remove play, which is all too often found on collapsible stocks. It has a removable recoil pad, sling loop, quick detach swivel sling mount and quick release lever, which unlocks the Cam-Lock and indexing pin with one motion.
One of its more interesting innovations is that it fits both mil-spec and commercial buffer tubes. (You’d think other manufacturers might have figured this one out. But you’d be wrong.) The Rogers buttstock is also standard equipment on Wilson Combat AR builds. If the stock is good enough for Mr. Wilson, it’s certainly good enough for me.
We also decided to revisit a company with the unsual name of Umbrella Corporation, which manufactures Grip 23. Grip 23 is an attractive product but ergonomics are a better reason to consider it. The geometry on this item differs from what you find elsewhere. There’s a more vertical angle (see photo) which fosters an ‘elbows down’ shooting position.
It simply feels more natural and we discovered, it lessens wrist fatigue. The is especially noticeable when shooting offhand.
The surface texture of the product is quite smooth and feels comfortable. The grip is made of a very robust polymer but it has just enough “give” to offer a perfect fit. If you feel the need you can stipple the grip—or not.
We thought Grip 23 added a handsome touch to our lower receiver “ensemble”.
Grip 23 is an unusual name and after doing a little online research we discovered what the origins were. Before this particular version was selected for final production, a number of prototypes were fielded and tested. The final variation, Number 23, was chosen after extensive feedback.
Miscellaneous Parts Department
Primary Arms, a company known mostly for it affordable optics also has a wide selection of AR 10 and AR 15 parts at excellent prices. (One of the buffers for our build came from Primary Arms). They carry a wide array of products — everything from BCGs to buttstocks to uppers from companies such as Bravo, Daniel Defense, Magpul, Troy and others.
With both lowers complete, our next step will be to test the two lowers with an upper receiver that we built from Aero Precision. Stay tuned for part 3 of this series.
Top photo: Completed JMT polymer lower.