My First AR-15 Walkthrough: Lower Construction

Parts were acquired, tools were assembled, research had been conducted, and my workspace was located. The preflight checklist was complete, it was time to actually begin.As prepared as I was, you’d think this was a huge undertaking somewhat akin to orbital rocketry, or deep sea exploration. Really, this whole process ended up feeling more like following directions on a Lego set, than truly “gunsmithing”. Though you want to make sure you’re paying attention, building an AR-15 is quite beginner-worthy.

While it doesn’t appear to truly matter where you start on the lower build, literally every guide I have seen so far begins with the magazine catch. I assume this to be rooted in the desire to have it adequately functioning so you can use a vice block to hold your lower for the remainder of construction. Again, this isn’t a bad idea. I’m going to look into it for further builds, but I managed to get through this entire run without one. It is a luxury rather than a necessity. The Spike’s Enhanced LPK comes with a milled aluminum mag catch button that comes without the drilled through hole found on most. This means that instead of simply screwing the catch into the button until it is flush, I inserted it until the screw bottomed out and backed it off until it aligned properly. Step 1: complete. I can get the hang of this.

Grippy and beautiful

Milled Magazine Release Button

From there I moved on to installing the trigger guard. Honestly, this piece confuses me a little. I didn’t realize there was so much demand for minute differences in trigger guard shapes to require this to be a modular piece. For all that, I guess options are a good thing. This piece actually gave me a little trouble to install correctly. Thankfully, this wasn’t the trouble that everybody seems to warn builders about. The ears that support the trigger guard on the grip side are fairly small and, according to reports, easy to bend. You want to make sure that these are adequately supported before you apply any pressure to them during installation. I just used a block of cut down 2 by stock. No, my only trouble was trying to get all the holes to line up appropriately. The small rubber pads on the Spike’s Gen 2 Enhanced trigger guard provide just enough pressure against the receiver to add difficulty to the install. I’m not really sure why they have been added, but I suspect that it provides a much more secure fit eliminating any possible slop. Once I correctly determined the install orientation, and overcame the prodigious dexterity required to keep everything lined up without using a vice block, installation was really straight forward. Just drive the included pin through the holes until the detent grabs hold of it to keep it secure. That detent is part of the charm of the Spike’s Enhanced setup, since it will prevent the pin from walking out during the rifle’s life span. I’m not entirely positive that releasing the front detent will actually allow the guard to pivot out of place (also thanks to the rubber pads), but I’m also not sure this is a feature I’ll ever need.

Check out that logo!

Billet Aluminum Trigger Guard

The Bolt catch in the Spike’s kit doesn’t appear to be any different than any standard bolt catch, and so every set of instructions I found online were all perfectly applicable. This is a really REALLY easy step on which to scratch your receiver, so extra caution is highly recommended. Tape that sucker up, good. I personally found trying to use a hammer and punch to be incredibly cumbersome without the addition of a roll-pin starter punch. For me, it was far easier to just use a pair of bent needle nose pliers and pinch the pin into place.

Pivot pin installations are by far the easiest place to accidentally lose pieces of your build. Those tiny springs and even smaller detents are impossibly small, and placed under a high quantity of potential energy during installation. I found it easy enough however to just use the flat of a retractable razor knife to hold the detent in place while installing the front pin. Done. Side note: this is the only portion of the lower build that I’m not 100% happy with. My front pivot pin fits tight. Too tight, from the feel of things. I can push it into place easily enough, but I can feel it begin to bind right at the end of its travel. Removing it however requires far more effort. I can’t actually pull that pin entirely without resorting to a hammer and punch. I’m going to try and clean up the holes a little and see if I can get things moving again, but for the time being, I’m glad I only own one upper and won’t have much reason to actually pull this pin.

Next up was the trigger and hammer assemblies. These were by far the most…interactive part of the lower build for me. Turns out, when they mention that you need to have the wide end of the disconnector spring pushed into place in the trigger, you shouldn’t gloss over that part and miss it. Pay careful attention to the little details people. Don’t try your assembly when you’re rushed or you’ll just get frustrated and screw something up. Thankfully I didn’t get to that point before I figured out my n00b mistake and set things aright. Even then, it took some finger gymnastics to get everything lined up properly. My Spike’s Enhanced kit included a special set of anti-rotation/anti-walk pins for this step that required just a little more effort than standard friction fit pins. The KNS kit includes a special brass tapered head to aid in installation of these pins, theoretically assisting in aligning the holes as you drive the pin home. I say theoretically because it really didn’t work out that way for me. The brass head ended up being more of a hinderance than a help, catching on the hole edges and gouging until it stopped the pins rather than guiding them in. It didn’t take me long to ditch it and proceed manually. Tap the pins in, install the caps on the KNS kit, and test the function. Just be careful not to let the hammer drop at speed onto your unassembled lower because you may deform the mag well where it makes contact. Guide it down with your fingers while testing in this phase.

The most complex portion of AR lower construction.

Fire Control Group

Installing the safety selector wasn’t exactly a piece of cake either, but again, none of this can truly be considered hard. It just took some odd jiggling before I managed to wrangle everything into exactly the right position to slide the safety fully through the opposite side of the receiver. If these little setbacks are the hardest part of this build (they are) then this whole thing is truly ripe for the hobbyist. Once again though, the Spike’s kit shines as more than standard here. My safety selector was actually an ambidextrous model, so there was the one extra step of installing the switch handle on the opposite side before I could call this complete. Once again, don’t forget to test for function.

More Billet Al and added functionality

Mag Release, Trigger Pins, and Ambidextrous Safety

Pistol grips have to be about the easiest portion of the build, even with the addition of the safety selector detent. There was nothing out of the ordinary. Installing the buffer tube and takedown pin as well went exactly according to the video instructions I found. Even trading the default buffer with the Spike’s Tactical T2 Heavy Buffer was no issue at all. Finally, I was able to slap on an old standard stock that a friend gave me. It’s literally the most basic adjustable stock available, so hardly worth mentioning. I’m pretty sure he scavenged it from an old S&W M&P-15 when it came time for upgrades. If anyone wants to sponsor a better stock, I’ll happily move up the ladder. In the meantime, this fits my needs.

Well, lookie there. That’s it. With that, the lion’s share of actual assembly on an AR-15 is done. I really couldn’t believe it was that simple until I tried it for myself. My thought always was “You’re building a gun, it’s going to be impossibly complex.” That just simply wasn’t the case. At least not yet. I guess I shouldn’t count my chickens before they’re hatched. I still have the upper to go.

Everything So Far.

Fully Constructed Lower

Parts in this article:
Stripped AM-15 Lower Receiver – Anderson Manufacturing
Buffer Tube – Mil-spec provided by Anderson Manufacturing
Lower Parts Kit – Enhanced LPK provided by Spike’s Tactical
Buffer – T2 Heavy Buffer provided by Spike’s Tactical

Bookmark the permalink.