Editor’s Note: Building out an Aero Precision M5E1 AR 10 upper is part 3 of a DIY AR 10 build series. We began by finishing two 80% lowers—a polymer receiver from James Madison Tactical and, a conventional aluminum unit from 5D Tactical. Both lowers were then assembled with lower parts kits, drop in triggers, buffer tubes, buttstocks, etc to create two complete lower receivers.
In this article we complete the second half of the rifle by building a complete upper with a parts kit from Aero Precision and, mating it with the previously built lowers.
Aero Precision is one of approximately 400 AR15/AR10 manufacturers in this country. It’s well known on the West Coast but may not have the national profile of other companies. There’s a reason for this.
Rather than put their money into PR or advertising, AP puts their dollars into R&D and manufacturing processes. Perhaps Aero Precision management is not fixated on tooting their horn because they already are an OEM for some of the top brands in the nation. (Of course AP would not be happy if I told you who these name brands were).
The company (as the name implies) has its roots as an aerospace subcontractor. (Boeing is about 45 minutes up the freeway). Not surprisingly, AP’s engineering prowess has made its way into the company’s firearms business. Airplanes that aren’t manufactured to the highest standards don’t stay in the sky.
Visiting the company’s offices in Tacoma earlier this year I had a chance to talk to employees and soak up the vibe. AP reminds me of a Red Bull-fueled Silicon Valley startup rather than some provincial firearms company. Their offices are modern, sleek and full of gun geeks at work stations.
There’s entrepreneurial blood flowing in the veins of this innovative, engineering-driven company and their technology manifests it.
Case and point.
I sat down with Bob Crisman, whom I’d met at SHOT a few years ago and he showed me, at his desk no less, how easy it was to install the barrel into an M4E1 enhanced upper receiver. This was a revelation because adding a barrel to a traditional receiver can be an onerous task. However, it is made much easier by AP because they have integrated the barrel nut inside the upper. All you need to do, as Crisman demonstrated, was to correctly insert the barrel assembly into the upper, line up the index pin and then tighten up the barrel nut.
A few Torx screws later you’ve got a complete upper with a modular, free-floated handguard.
I was blown away.
“Of course, you need the tools”, said Crisman but the whole thing could be put together in less than 10 minutes.
When Bob showed me how straight-forward it was to assemble the upper I thought this would be the perfect complement for our DIY 308 project. I also reasoned that if I could put this together (with my limited mechanical skills) anyone could.
Getting to know the M5E1
Instead of building AP’s M4E1 upper (AR 15 upper) as Bob demonstrated, I was interested in assembling their M5E1 (AR 10) upper. Like its AR 15 sibling, the M5E1 enhanced upper receiver is a one-piece design that combines the handguard mounting platform with the upper itself. All you need to mount the free-floated handguard are 8 (Torx) screws. AP states because the handguard mounting surface and upper are of the same forging, the rifle is stronger, lighter and cooler to run.
So let’s examine the components:
The barrel is a medium profile 16 inch Tactical Government Profile machined from 4150 Chrome Moly Vanadium steel with a QPQ Corrosion Resistant Finish and QPQ coated M4 feed ramp extension. It’s not exactly a lightweight but at 35.9 oz it’s not as front heavy as you might think. It has a one in ten twist, which is pretty standard for 16 inch barrels. The manufacturer of the barrel, Ballistic Advantage, which is a majority owned subsidiary of Aero Precision, guarantees a sub moa at 100 yards, if you use the proper ammo. If there’s an issue they will check it out for you and if necessary, replace the barrel.
I thought that was pretty reassuring.
The kit comes with a low profile gas block, a mid length stainless steel gas tube and a hefty, easy-to-grab ambi-style charging handle, made from forged 7076-T6 aluminum–all of AP’s manufacture.
The M5 15 inch keymod handguard is one of AP’s new Gen 2 series. (There’s also an enhanced M-LOK version). These fit the DPMS pattern and feature quick disconnect sling sockets at the 3, 6 and 9 o’clock positions as well as a DPMS “High Profile” (.210) Tang. Atop is a 1913 style rail. The rail is not monolithic but has material strategically removed to save weight.
The handguard slips seamlessly over the forged, anodized 7076 T6 aluminum upper receiver. It’s pre-assembled with a port door and forward assist.
We opted for AP’s flip-up sights and their standard phosphate BCG which has a chrome lined carrier and gas key. The bolt is made from 9310 Steel and is high pressure tested and magnetic particle inspected to make sure there no fractures. The extractor is made from 4340 steel and is manufactured with dual “O” rings and dual springs to ensure solid extraction.
The whole shebang, without magazine tips the scale at just over 8 lbs, which is not bad for a Ar 10.
You’re going to need the right tools to get started and Bob provided me with the following list of his preferred items:
- Bench Vise
- Geissele Reaction Rod for AR10/SR25
- Torque Wrench
- An AR15 Armorer’s Wrench (Tapco preferred)
- T15 Torx Driver
- Gas Block Roll Pin Punch Set
- Nylon Brass Hammer
- Anti-Seize Grease
We had our own selection of tools which varied slightly from the suggestions Bob made. Instead of the reaction rod, we used an AR10-AR15 upper receiver action block and a barrel wrench made by Precision Reflex.
We had several AR15 armorer’s tools other than the Tapco model as well as AR barrel nut tools. The one we choose was manufactured by Precision Reflex.
We had a torque wrench from Tekton and one from Wheeler Engineering as a double check.
Putting the Upper Together
There’s no official documentation (yet) from AP to assemble the upper but Bob was kind enough to provide some direction.
Our first official action was to add a smidgen of high temp aircraft grease to the outside surface of the barrel extension and then insert the barrel (as illustrated above) into the upper receiver by lining up the index pin (on the barrel) with the corresponding notch (at the 12 o’clock position) in the receiver.
We made certain the pin was at the 12 o’clock position. If not, it’s possible to sheer off the pin or even damage the slot in the receiver.
This is really the heart of the install. It’s not that difficult. It just needs to be done properly.
We then applied a little grease to the inside threads of the barrel nut and hand tightened it onto the barrel. It took us a while to make sure that our barrel nut wrench tool was mated properly with the teeth on the barrel nut. This took some gentle tapping with a rubber mallet but eventually we got it secured.
Setting our torque wrench set at 65 ft lbs, which is what Bob recommended, we cinched down the nut and attempted to align it properly so that there was room for the gas tube. At 65 lbs we torqued the barrel nut, and then backed it off again to finger loose, 8 – 10 times, trying to settle the threads and the barrel in place, and get to the point where we might be able to back off on the torque to the recommended spec.
However, we were not able to get it down below 70ft-lbs during our first assembly session, and still allow the gas tube passage through the nut/receiver 70ft-lbs, just barely allowed the gas tube to pass within the receiver so we moved our wrench up to 70 and then 75 lbs.
We kept our fingers crossed.
The rest of the assembly, which entailed inserting the gas tube, went smoothly. We used a a roll pin holder/punch and our brass hammer, to set the set pin in place to secure the gas tube.
We then slid the handguard over the barrel into position on the receiver and tightened the 8 T15 Torx screws into place.
The final act was to install the shiny stainless steel muzzle brake from Xtreme Precision. This entailed adding a crush washer on the business end of the barrel and essentially crushing it by torquing down the brake with a 19mm open ended wrench.
So far so good.
The next step was to mate the lowers with the AP upper.
The polymer unit from James Madison Tactical had a snug, “Golidlocks” fit. We were able to add and remove the take down pins easily.
The aluminum lower from 5D Tactical was another story.
It was tight–so tight that I nearly gave up on it. At first I considered having my smith remove some material from the lower receiver but I didn’t want to adulterate anything if I didn’t have to. He suggested instead tapping the take down pin with nylon hammer and a punch first, and then similarly, tapping in the pivot pin.
We did this without really forcing the issue. That said, it wasn’t the best scenario. You should be able to mate and decouple the rifle without having to use a hammer. (Who carries a punch and a mallet in the field anyway?)
Not ideal. What to do?
Dave Cannon, founder of Xtreme Precision which manufactures LPKs for the DPMS platform, had a better solution.
His fix was to take some material off the offending takedown pin. The caveat is that you’ll need a set of stainless pins to do this otherwise your standard pin, once the coating is taken off, will rust.
How to remove a bit of metal off the pin? You can do with some emery cloth and an engine lathe. Or, Bubba-style, you can fashion your own DIY engine lathe. Just put the head of the pin in the chuck of a cordless drill.
This fitment issue often rears its head in the .308 AR universe and DIY builders need to be cognizant of this.
Difficulties with upper/lower fitment are all too common with this platform. Companies that manufacture 80% lowers understand this. Andy Perry, one of the owners of 5D Tactical, told me that in testing upper receivers for his 80% lower receiver kits, some uppers simply did not fit.
Fortunately, after a little tweaking, things worked out just fine with our Aero Precision upper kit and our two DIY lowers.
Building the upper and matching it with the lower proved to be more complicated than planned. (Not exactly an unusual situation!) I had a number of queries and called both companies (Aero Precision and Ballistic Advantage) for advice. I did not disclose, until the question had been answered, that I was a journalist. The phone was readily picked up in both instances. The folks on the other end were polite and knowledgeable. I don’t think you can ask for more.
Stay tuned for part 4 of this series. In our next post we’ll customize the rifle with optics, trigger, buttstock, sling and magazine. Then we’ll take it to the range and see what our homemade gun can do.