I’d bought an Aero M5 lower receiver on sale a while back and decided to build it. Over the years, I’ve assembled a couple of M4s and one M5 where I bought an assembled lower and upper but this was my first actual build. I’ve always found the quality of the Aero parts to be good and they definitely made some unique tweaks to their M5 vs. their M4.
Rather than “yet another post about how to build an AR”, I decided to comment on the differences I noticed about the M5 lower. In general, the AR10-series of weapons aren’t standardized and you have no guarantee that parts from different vendors can interchange so you need to do some research and plan your build.
It is a DPMS Gen 2 pattern lower with Aero’s own spin on it. With that said, even though it is patterned after the DPMS, verify any other brand parts before you try to use them. I can tell you that AR grips and stocks work plus triggers.
I opted for a 16″ Aero upper, bolt, charging handle, recoil spring, buffer and lower parts kit. However, I had a Trigger Tech Duty trigger pack I wanted to try out plus I wanted to use a Magpul grip and UBR stock. The UBR has been on my radar for years but hadn’t tried one before now.
It starts with a pile of parts.
The pile was getting more organized. Huh … I had two LPKs – one with a Magpul MOE grip and one without. Well, spare parts never hurt … especially when the detents launch into orbit…
A Closer Look At The Aero M5 Receiver
It is a forged receiver using 7075-T6 aluminum and that is just fine. Now, arguing forged vs. billet will start all kinds of arguments about which is stronger, lasts longer, can solve world peace, etc.
Ignore the marketing and people weighing in on forums who have no idea. From a purely practical perspective, buy a receiver that you like the looks of from a reputable firm and have read reviews about. Honestly, forget about forged vs. billet. End of story.
There are plenty of other things to worry about rather than theory vs. practical reality. A receiver is just part of the puzzle that includes the other parts of the firearm, the ammo, the optics, you (the shooter), the environment, the situation, and far, far more.
It’s a gracefully executed design. You can see the large flared mag well,the stylized “A” for Aero symbol, the integral oversized trigger guard, a shoulder screw is used instead of a roll pin for the bolt catch, pictogram around the selector, the rear takedown pin is oversized, and the buffer tube has a flat area on the side. Everything is nicely machined and the anodized surface has a nicely done uniform finish.
The bolt catch having a shoulder screw makes that part of the assembly very easy not to mention lowering the odds of scuffing the receiver if someone lacks the proper tools. The M5 just requires a 1.5mm hex head bit. In this case, I am using one from my Strebito precision screwdriver set.
Ok, did not expect this. The front detent spring and pin go in through the boss. It’s not exposed like an AR15/M4 so none of my regular tools would work.
I used a 1/4″ clevis pin to go through the bosses, I pushed the pin and spring down with a thin hex key while sliding the pin forward. The pin then captured/retained the detent and spring. I then carefully slid in the front takedown pin while keeping the clevis pin pushed against it. Once the channel in the pin was over the detent, it sprang forward and everything was set. I carefull rotated the pin to make sure the detent was in the channel and then pushed it into the open position to make sure the takdown pin was correctly captured.
There are two changes I want to point out in the grip screw area. Just to the right of the grip screw hole is the bottom of the nylon tipped tensioning screw. Before you install everything, install your upper and adjust this screw to get the tension you want so the upper doesn’t rattle. Too much tension and you will not be able to disassembe the rifle without a punch if at all. Note, I have the selector detent in there. I dumped it out before I flipped it over to install the upper. The hole to the right of the selector detent is the takedown detent hole. Because the M5 lower is longer, putting it here makes sense. Aero does have it tapped for a 4-40 set screw so you can elegantly capture the detent spring if you want to. Note, you do need to trim the detent spring level with the receiver using some nippers before you install the set screw if you go this route. Oddly enough, my lower parts kit either did not have the set screw or I lost the set screw so I did not go that route.
Here’s the hylon-tipped top of the tensioning set screw.
I set the tensioning screw just enough so the upper didn’t rattle but also such that I could push out the takedown pin by hand. Since I lacked the 4-40 set screw to capture it, I just juggled both detent springs as I installed the pistol grip. It wasn”t too hard actually but the set screw would definitely have made it easier.
Summary
First off, kudos to Aero for another fine set of parts. I found the small differences with the Aero M5 interesting. Aero Precision turns out quality – I’ve owned various ARs and even have a .308 Solus bolt rifle from them right now. I have no hesitation recommending their products.
I hope this helps you out.
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