There are almost as many ways to build an AR-15 as there are parts combinations. Today, however, we’re going to focus on the three most popular AR-15 build styles.
Let’s get right into it.
AR-15 Build Styles
1. Pre-Assembled Lower + Pre-Assembled Upper
The simplest choice is to buy a pre-assembled lower and mate it to a pre-assembled upper. This is technically “building” an AR from a legal standpoint, as it avoids the 10% ITAR tax on the sale of a complete rifle.
This might be a worthy reason for doing your build, assuming your goal is a mainstream desire. You also have some degree of control over the options you choose to mate together. This method is inherently limited to the options bulk builders see a market for.
It is rare that you will find many of the higher-end options in these offerings. The good news is that all uppers will mount to all lowers, assuming they are not from a third-rate manufacturer or not specifically labeled as being proprietary.
(This is of specific concern with pistol caliber lowers and some billet components.)
2. Prebuilt Lower or Upper + Other Parts
A slightly more labor-intensive option among AR-15 build styles is buying either a prebuilt lower or a prebuilt upper and assembling the other half from parts. Many people do this when they find desired components in a preassembled half, but not in the other half.
Most of my AR builds fit this pattern. Although I am fully capable of assembling an upper, a prebuilt upper matching my desires usually costs less and is the manufacturer’s problem if something doesn’t work properly.
Prebuilt lowers rarely come with quality triggers, so I usually build those myself.
An example: I priced out buying the components for a 24″ heavy barrel precision upper build. Buying the components I wanted, would have cost me roughly $1,000. Instead, I bought a fully assembled White Oaks Armament upper for just under $700.
The only thing I wasn’t entirely sold on was having a tube handguard instead of a railed one. I have come to learn that a tube on that type of rifle it is a great option.
In addition to saving $300 and the time of assembly, I also received the White Oaks Armament reputation for accuracy. My sub-MOA expectations were handily exceeded with hand loads. When I do my part, the rifle provides sub 1″ five-shot groups at 200 yards.
Occasionally, the group size hits .625” at 200 yards. I seriously doubt any assembly of parts would do as well. In my three years of owning this rifle, the only thing I have changed on the upper is having the barrel threaded for suppressed use.
In this example, I knew the barrel and chamber were going to be spot on, so the best use of my money was to make sure the lower components’ performance matched with the potential of the upper. This meant I needed a quality stock and trigger.
On a build with a 7# upper, a light collapsible stock was not the best idea. It also meant that a Mil-Spec, 8# gravel road trigger was not an option. The $300 saved on the assembled upper went a long way towards building the lower properly.
This included purchasing a Magpul PRS stock, high-quality lower parts kit and one of Geissele’s SSA-E, two-stage triggers.
3. Complete Build from Scratch
The last general category of building your own AR is to buy a basket of parts, assembly tools and get building. A list of those parts can be found here.
I would strongly suggest not taking this route on your first build. It would also be smart on the initial build of this type, to not use generic brand components. These parts have a much greater chance of being out of spec and creating assembly issues.
As a new builder, it is unlikely you will be able to easily diagnose the issue and may well spend more money chasing the issue than if an assembled gun was purchased. The worst of the potential issues is out of spec head spacing.
This brings me to the point where I give the safety brief. Every build has the potential for error. Some errors result in a scratch on your lower or upper—frustrating, but not a big deal. Others result in a broken or lost component. Annoying, but not tragic.
The worst issues result in out-of-battery ignition, dramatic overpressure situations or other potentially catastrophic events.
If you’re interested in getting a taste of what this looks like, here’s a video example of one sequence in building an AR-15 from scratch (installing the takedown pin and buffer tube):
Essential Tools for AR-15 Builds
If you are doing anything beyond mating a pre-built lower to a pre-built upper, you really should have some AR build tools and one specific safety item. Here’s what you need for most AR-15 build styles:
- Caliber-specific headspace gauges – this ensures the round chambers properly and having this within spec will eliminate most potentially catastrophic issues. This is the safety item.
- AR Armorer’s wrench – very helpful in doing many of the fiddly assembly components of the upper, getting them properly mated and tight
- Punches – specifically, roll pin punches
- Upper and lower AR vises
- Pivot pin tools
- Well-documented assembly video series – from a reputable builder, parts company or wholesaler
Whichever method you choose, there is a great degree of satisfaction in building your own AR. It also opens up the build possibilities, be that for a specific component or building an AR in a non-standard caliber. My next build is likely to be a .458 SOCOM pistol.
I plan on running a Faxon 10.5” barrel, Fail Zero nickel boron bolt carrier group, Brigand Arms 9” ATLAS handguard, Spikes “Honey Badger” lower, Geissele SSA-E trigger, Magpul BAD lever and a Gear Head Works Mod 2 Pistol Brace.
What is your favorite among the above AR-15 build styles? Let us know in the comments below!