There is no more daunting goalpost in the gun community than assembling or otherwise building your own AR-15 but, by keeping in mind some basic considerations and doing your homework, that goal can be easily attained.
In This Article:
AR-15 Build Kit Comparison
Below is my list of the best AR build kits for 2021. I list the best choices in terms of value, performance, design, and cost.
Click on the name to head to the product page, read reviews and check prices or skip ahead to the list of build kits.
|PSA AR Rifle Build Kit||Best Complete Build Kit|
|Aero Precision M4E1 AR Builder Set||Best Builder Set|
|Brownells AR-15 LPK w/ Geissele Trigger||Best LPK|
|Timber Creek Outdoors Enforcer AR-15 Build Kit||Best Custom Build Kit|
|CMC AR-15 Lower Parts Kit w/ Triggers||Best Trigger Kit|
|Geissele Ultra Duty Lower Parts Kit||Best Small Parts Kit|
|AR-15 Lower Parts Kit w/ Geissele Rapid Fire Trigger||Trigger Runner-Up|
|AR-15 Lower Parts Kit w/ Two-Stage Geissele Trigger||Best 2-Stage Trigger|
AR-15 Build Kits Reviewed
1. Best Complete Build Kit: PSA
Palmetto State Armory at any given time has a dozen or more AR-15 kits up for grabs in pistol and rifle format. One of the best bangs for the buck is their Lightweight M-LOK kit which includes a nitride treated 15-inch 4150V chrome-moly steel barrel, chambered in 5.56 NATO, with a 1:7 twist, M4 barrel extension, and a carbine-length gas system.
As it includes PSA’s Classic Freedom Lower Build Kit along with a full-auto profile BCG with a 9310 bolt, all you need is a lower and the time to build it up. In short, this is as close to an AR-15 in a box that you can get.
2. Best Builder Set: Aero Precision
A household name in the AR receiver game, Aero Precision can set the home builder up with both an assembled upper — with forward assist and dust cover installed — and a stripped lower combo set that won’t break the bank.
It comes standard with a nylon-tipped tensioning set screw in the grip tang of the lower to aid in fitment between the receivers and M4 feed ramps.
3. Best Lower Parts Kit: Brownells
Bravo Company has dozens of upper receiver groups running from short 9- and 10.5-inch pistol uppers to 20-inch rifle models in a variety of calibers.
About the most-feature rich of these is their Kyle Defoor KD4 series uppers with SS410 barrels, ideal for use with 77-grain pills.
4. Best Custom Kit: Timber Creek
Diamondback Firearms in Cocoa, Florida is one of the fastest-growing black rifle makers in the country, and for good reason– they are good at what they do and make a quality product that eschews the sometimes-inflated prices of their competitors. This is why they offer basic LPKs, including grips, for about $50 and more comprehensive ones including Magpul furniture for about $100. Likewise, they run similar deals on both stripped and complete uppers.
5. Best Trigger Kit: CMC
6. Best Small Parts Kit: Geissele
Pennsylvania-based Geissele is well-known in the AR-15 market even if they have gained something of a reputation of being a bit on the expensive side.
The good news is that their Super Duty and Ultra Duty lower parts kits are affordable and offer a great value. Add one of their buffer tube sets on a stripped lower plus a grip and mag and you are ready to finish it out with the upper of your choice.
7. AR Trigger Runner-up: Geissele SRF- Brownells
For roughly the cost of one of Geissele’s SD or UD kits, Brownells offers a lower parts kit paired with one of Geissele’s glass-smooth and fast-shooting Rapid-Fire Triggers, which can be tuned in either 3.2- or 4-pounds by swapping out the included trigger springs.
While the Rapid-Fire Trigger pulls like a single-stage, it resets like a two-stage, making it ideal for many better builds.
8. Best Two-Stage Trigger Kit: Geissele + Brownells
Suppliers of high-end precision-driven AR platforms to the British military and others, LMT Defense offers both a complete lower parts kit that includes their two-stage trigger group and what they bill as their “Light” kit that comes sans trigger group to allow builders to make that personal decision themselves while still having LMT internals in their lower.
What is a build kit anyway?
In short, unlike a complete rifle or pistol, AR-15 build kits are more on the component side of things, with varying degrees of “some assembly required” to finish the gun into a range-ready firearm.
These range from joining up a complete lower to a complete upper and adding a magazine and lube– possibly the easiest level– to building an AR from the ground up. Then, of course, there is everything in between.
Of Uppers and Lowers
For those who skipped AR-15 101, the platform is comprised of not one receiver as on most firearms, but two: an upper and lower.
Only one of these, the lower, is serialized and therefore considered a controlled item by ATF. Each can be purchased “stripped,” which requires further building out, or complete, which only requires final match up to be ready to roll.
Keep in mind there will typically be some minor “play” between uppers and lowers, especially if you select them from two different manufacturers, a factor that can be alleviated by picking up a set of matched lowers which have been machined to tight corresponding tolerances to eliminate the “slop.”
Upper receivers can be challenging. By far, a barreled upper is an easier learning curve to work with, especially for those who are on their first build and allow the builder to avoid having to pick up a torque wrench and reaction rod.
Also, with the barrel already installed right out of the box by a reputable firm, it alleviates the worrisome question of having the correct headspace in the chamber. While starting with a stripped upper is more of a heavy lift for inexperienced builders, it does allow much more customization when it comes to barrel choice.
When it comes to lowers, forged 7075/76 aluminum lowers advertised as “mil-spec” should be the baseline for a build, while a lower parts kit, buffer tube, and stock/brace are not an overly complex task to install correctly. There are any number of helpful (free) videos out there to walk you through it — and we have a complete visual guide on assembling an AR if you’re so inclined.
As a tip, threaded trigger guards are great as they keep you from having to drive a roll pin through that somewhat easy-to-break ear with a hammer. Likewise, when you install the buffer tube and receiver extension, be sure to apply a serious stake to the castle nut to avoid having it unwind with vibration while in use, which is a bummer.
What to Look for in a Quality AR Build Kit
These days, many AR owners typically begin their pursuit of the ArmaLite-style rifle by acquiring one or two complete guns then balancing out their collection with at least one or two personally assembled guns from kits and taking it from there in either direction.
The primary reason for branching out to a kit build is that the builder can research and carefully pick every single part as they go, optimizing the build for a set purpose (more on this later). The result can range from the beautiful to the comical, and span from low-tier budget to super Gucci custom– all with the easy tweak of a handful of parts and components.
Few constructions in the consumer marketplace offer such variety. Additionally, the build process instills the builder with a skillset and knowledge base that takes them far beyond the basic understanding of manipulation or nomenclature and allows them to supervise as much of the production of their gun as they want.
They are responsible for the staking of parts. They are the one who installs every pin and spring in the lower. This makes the satisfaction of producing a working firearm a very personal, and often fulfilling experience: a journey into ballistic self-improvement if you will.
The correct first step in any build is to define a list of expectations for the result once the final lube is added and the gun is function checked. Plan out your build in a road map of sorts by making a build list from the raw receivers to the barrel, LPK, grip, handguard, BCG, muzzle devices, and so forth.
2. Rail and Optic Configuration
What kind of optic or sights will you be using? This will point to whether you want an A2, A3, or A4 upper and what kind of top or quad rail system it uses.
3. Length & Weight
Are length and weight a factor? This outlines how long a barrel is and the type of stock used.
4. Barrel Considerations
Do you intend to suppress it? This tells you if you want a threaded muzzle or want to use a QD attachment for the can of your choice.
Will you take it hunting where allowed– check your caliber choice with this– and if so, what kind of load will you use? This can lead to barrel length and twist decisions. If you’re looking for distance performance a 18-inch or longer Valk or Grendel upper might be appropriate, — but if you’re trying to keep your home safe or want a more truck-friendly build something like a .300 Blackout or traditional 5.56 upper would be a better option.
What is the purpose, for instance, will the gun be used sparingly as a range toy or will you stake your life on it in a potentially extended self-defense scenario? This will help you choose the appropriate BCG.
Common Mistakes & Considerations
Take everything you know about buying anything and throw it out the window when it comes to shopping for gun stuff, especially online.
Failing to research
While you can head to eBay or Amazon for just about any household goods you can name, prejudicial banking practices and deplatforming have driven many firearm industry vendors to more niche sites.
Further, shipping times are often longer and controlled items like finished lowers have to be transferred through federally licensed firearms dealers, adding extra steps to the process.
With that being said, don’t get in a rush. Do your research!
Skimping on the most important bits
Don’t grab a flawed, inexpensive heart and soul of the AR– the barrel and the bolt carrier group. This is where most of the wear and tear on an AR platform will occur because this is where the force of the cartridge’s ignition takes place and the action is cycled, with metal-on-metal contact.
As such, this is where catastrophic failures will most often occur. At a bare minimum, make sure the BCG is of good quality, from a reputable maker, and is Magnetic Particle Inspected (MPI)– sometimes just seen as Magnetic Tested (MT)– high pressure tested (HPT) and shot-peened (SP).
If you are on a tight budget, feel free to try to nickel and dime almost anywhere but the barrel and BCG, or save for a couple more weeks for something better.
Lack of tools
Once you get your components, make sure you have the proper tools to complete an AR build. Barrels will need to be installed and torqued down correctly, gas keys and castle nuts have to be staked, roll pins will require properly sized punches.
Minor investments in a bench block, a small table vice, an AR-15 armorer wrench/multi-tool, hammers (remember, nylon and brass are your friends here), correct-sized punch set, anti-seize compound/grease, clevis pins, and go/no-go gauges may seem daunting at first but will amortize out if you produce several builds over the years. Gunsmithing tools do not have an expiration date.
Check with your local gun store as, if they have a smith on staff, they often run build classes for a nominal fee if you bring your parts and will help with tips, tricks, and the loan of some of the more rarely used tools. Expect to do all your own work, however. Speaking of which…
Keeping it legal
With so many AR components out there, it is easy to goof up and accidentally stray into National Firearms Act (NFA) territory, which can end up with as much as a decade-long tour in the federal prison system.
Fundamentally, when it comes to lowers, if it is sold specifically as a rifle lower, it needs to stay a rifle lower for its entire existence.
The same goes for pistol lowers. When matching the two receivers up, keep those NFA regs in mind to ensure you stay away from having an illegal AOW or SBR unless you have an approved Form 1 beforehand.
Going even further, accessories can run afoul of the law as well, for instance attaching a vertical foregrip or an M4 stock to an AR pistol. Also, when counting a muzzle device into the minimum overall barrel length of a rifle, be sure that device is permanently attached– just adding some red Loctite doesn’t count.
When in doubt, check it out before you build it. The last thing you want to do is go to some public shooting range somewhere where a photo of you and your questionable kit makes it into circulation.
Also, remember you have not only federal law but in many areas state laws that may affect your build. Finally, be sure you are building for your personal use, rather than to sell the finished product specifically for a profit– which can bring unwanted scrutiny from the alphabet guys.
In short, know what you are buying and building.
- YouTube, LPK Installation Videos
- Stag Arms Blog, The difference between Gas Piston and Direct Impingement technology for an AR-15
- ATF, ATF Form 1, Application to Make and Register a Firearm
- Gun Trust Guru, Can I Add a Vertical Fore Grip to My AR-15 Pistol?,
- ATF, If a person has a pistol and an attachable shoulder stock, does this constitute possession of an NFA firearm?
- ATF, Definitions of a Firearm
- ATF, What does “any other weapon” mean?
- ATF, ATF – National Firearms Act Handbook
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