The time has come. Since you’re here, you probably decided to embark on the hardcore adventure of building your AR-15 lower receiver from scratch using a lower receiver parts kit. You’ll need full immersion in the process, good hand skills, and great focus. These will help you succeed only after you manage to get the best AR-15 Lower Parts Kit (LPK).
The idea that you can build an AR-15 yourself and it can perform better than the ones that come pre-built is very appealing to gun collectors, outdoor enthusiasts, and range shooters. Not only does it perform better, but it’ll also be customized to your liking (and with a significantly lower price)!
In reality, you cannot assemble a high-functioning AR 15 rifle without quality precision parts. You’ll want to look for lower parts kits that provide you with the integral parts, pins, and springs needed to complete your lower receiver to perfection.
Let’s go over what a quality lower receiver parts kit includes:
Some Important Info For AR-15 Lower Kits
What parts should you expect to find in many AR-15 lower parts kits?
Keep in mind, some lower receiver parts kit advertise themselves as “AR build kits”, which are good for starting a basic AR-15 rifle build before gradually improving upon it with customizations / add-ons. Some are more or less complete with certain parts included. For example, some AR-15 lower build / parts kit include a trigger while others may not. This is because the trigger is considered to be such a highly individualized part that the user should probably order one separately.
On the other hand, a “mil-spec LPK” includes a single-stage trigger plus factory pins, springs, detents, and other parts.
Some kits might not include a buffer tube, spring, end plate, tube nut, or stock. It doesn’t mean they are low-quality purchases. It just means they don’t have the specific parts that you need for your rifle. You have to understand what you need first. Some kits will generously include some extra parts / tools to help you when installing the pivot pin, for example.
Having said that, here is a comprehensive list of all the parts you should expect to find in most lower parts kits:
- Trigger (may not be included)
- Bolt Catch
- Pistol Grip (optional)
- Trigger Assembly
- Trigger Spring
- Hammer Spring
- Bolt Catch Spring
- Disconnector Spring
- Buffer Spring / Buffer Retainer
- Buffer Tube
- Trigger Pin
- Hammer Pin
- Hammer Sear
- Bolt Catch Roll Pin
- Rear Takedown Pin
- Detent Pivot Pin
- Takedown Pin
- Roll Pin
- Trigger Guard Assembly
- Bolt Catch Plunger
- Safety Selector
- Safety Selector Detent Spring
- Takedown Detents and Springs
- Magazine Catch Assembly
- Castle Nut
This exhaustive list of components might be intimidating to the average customer, but the process is truly easier than it looks, so please bear with us.
As previously mentioned, some kits might be missing part. It might be the pistol grip or the trigger, depending on the brand. There’s a course of action in each situation of these. The important thing is to know beforehand which parts don’t come with your kit.
In the AR 15 lower parts kit list we compiled below, we tried to offer you a range of LPKs with high-quality machining and performance. We chose the most comprehensive kits (from popular brands), and we tried to include kits for both beginners and pros. If you’re looking for affordable and easy-to-install kits, this list has you covered as well.
If this is your first LPK build, you will naturally want to get all the parts. But if you’re going for an upgrade, you’ll probably just need new springs and a bolt catch.
For newbies, we advise you to get a mil-spec kit (military specification), for they are pretty basic and straightforward. More importantly, they work well with all other kits, include the essential factory parts, and will save you some time / effort.
Lastly, we provide a list tools required to install your AR 15 lower receiver parts kit at the end of this guide.
Now let’s look at some popular brands:
The Top-Rated AR15 Lower Parts Kits
Armaspec AR-15 Lower Parts Kit
Armaspec’s AR-15 lower parts kit is entirely made of stainless steel to match the quality of your rifle. Stainless steel is durable and rust-resistant, so it’ll be a good choice.
To protect your lower receiver from being damaged by the pins, this kit from Armaspec comes with anti-walk pins. Overall, the kit is super easy to install. However, you might find it hard to move the takedown and pivot pin, which comes across as upsetting to many.
In fact, this is not a complete AR 15 lower parts kit. It does not include a pistol grip, trigger, or hammer. The disconnect spring alongside the trigger and hammer springs aren’t included as well. That’s why it’s rather a builder’s kit that you start with and improve upon.
When it comes to quality, we’d say that these parts are of average quality. They perform well compared to their price, but they’re for amateurs. On the plus side, they come with a lifetime warranty.
Stag Arms, AR-15 Lower Parts Kit
Another excellent building kit is this AR-15 LPK from Stag Arms. It includes all parts of a lower receiver, except for a pistol grip. The reputable name and expertise of Stag Arms in the industry are more than enough to trust their kits.
This kit works fine for upgrading or maintaining your lower receiver. It meets military specifications while paying extra attention to the trigger group and machined billet trigger guard and the billet magazine guard assembly that they call “enhanced.”
Stag Arms offers a limited lifetime warranty on its parts. You can refer to their website for details.
PSA MOE SBA3 Lower Build Kit
The PSA MOE SBA3 Lower Build Kit is more on the professional side rather than the beginner’s one. To start with, this kit was primarily built in response to the Elite Task Force Team’s needs, so you’d expect something big from that!
This PSA kit is also military standard, and you can use it to build the lower receiver of an AR or a pistol. Using the LBE kit, you can build 80% of your AR-15 rifle’s lower receiver. However, as you know, military standard specs aren’t the most outstanding when it comes to customization. They do perform well, but they’re pretty basic. So this kit serves as a great base for your lower receiver, then you can buy individual parts to fully customize it to your liking.
Not that the PSA kit comes with no trigger guard nor a pistol grip, so you’ve got to get these from somewhere else.
Because of the professional standards, this kit is about 10 to 20 bucks pricier than other kits, depending on the dealer. You’ve got to be an avid shooter to get something like this. Besides, we don’t think this is the best choice for beginners. It requires some prior knowledge and expertise in building ARs.
Geissele Automatics Lower Parts Kit for Ar-15
Geissele Automatic’s Lower Parts Kit is among the most popular on the market, and it’s easy to see why: each part is made precisely, and they’re of high quality and will fit flawlessly within your AR.
Geissele Automatic is primarily known for its 1911s. Yet, its optimal quality is passed to everything it produces, most importantly ARs. The LPK sports an elegant finish, and the parts fit well together. You have to keep in mind that the company is still dabbing in the field of AR, after all.
Check out our favorite red-dot’s here.
The missing parts in this kit are those of fire control; the trigger, hammer, disconnector, and springs. Yet, there’s a right-hand safety selector included, which is definitely a plus over other kits.
Geissele Automatic is among the companies that stand behind their products. Shall you receive any kit with missing parts, they’ll provide you with it promptly.
The unfortunate news here is that the Geissele Automatic are slightly overpriced. They do exude a premium quality that might be worth the price. However, there are nearly equally good parts that are not that expensive. It’s a matter of preference here according to your budget in the first place.
Palmetto State Armory MOE Lower Parts Kit
Palmetto’s MOE Lower Parts Kit is made to military specs, which means that its parts fit perfectly together. In turn, this will save you a whole lot of confusion and failed trials when you’re installing the parts.
If you’re not familiar with the MOE in the name, it refers to Magpul Original Equipment that is an established manufacturer and designer of firearm accessories. They’re mostly polymers, though. They’re known to be of reliable quality, and they fit quite well with the AR-15. Yet, when it comes to aesthetics, they’re not the most outstanding ones out there. If you’re looking for firearm accessories that stand out, you might entertain other options.
One of the merits of this kit is its uniformly cut detent pins. Moreover, the trigger is slightly better than the ones of kits in the same price range.
You’ll receive the kit covered in a thin oil coating that helps immensely during installation.
Finally, the best news is that this kit is of a significantly lower price than its counterparts. That’s probably because they’re made of polymers. Nonetheless, you get what you pay for, which is pretty convenient. To wrap it up, the Palmetto is a perfect pick if you’re on a budget.
Brownells Lower Parts Kit
We’re looking at a kit that’s made according to the military specs here. Despite being a tad more expensive than the other options on our list, Brownells LPK is one of the best on the market, with a premium quality that justifies its price point.
The main reason for the increased price is that it includes the buffer tube assembly that’s absent from most LPKs. It does include a Geissele rapid-fire trigger, MOE stock, and grip. A strong point that’s definitely in favor of Brownells, as well as a few of their other accessories.
Like most of the kits featured on this list, this too is more of a building kit rather than an advanced one. The parts come in separate color-coded bags for easy assembly.
The trigger guards are made of durable metal, but they’re a bit long, so they won’t fit with all rifles. You probably need to check that. Some reviewers reported trouble with the rear down pin and its plunger that they don’t fit well together; either the plunger is too small for the pins that the detent captures them, and they’re stuck, or that the detents are drilled too deep.
Pivot and takedown pins have heavy-duty steel retainers as opposed to brass ones found in other kits. Besides, the trigger guard is also made of sturdy material as opposed to flimsy polymer ones. If you’ve tried other LPKs before, you’d appreciate these features.
The overall consensus is that this is a kit whose parts fit in well with your rifle.
Aero Precision Standard Lower Parts Kit
Aero Precision Standard LPK is also a reputable kit manufactured with military specs to fit with almost any rifle.
This set comes with a 4-40 set screw to help with the retention of the threaded rear takedown pin of some Aero models. The Aero set excels in that it comes with every little thing you need to build your rifle’s lower part, all sealed in a heavy-duty plastic bag. A buffer retainer, pivot pin, trigger pins, hammer spring, disconnect spring are just some of the essential parts included. You won’t be missing any little bits or bobs anywhere. We promise!
The parts are somehow heavy but “good heavy.” We won’t object to that. Our concern about the Aero parts is that they don’t fit quite well with parts from other kits.
Midwest Industries Lower Parts Kit
This LPK from Midwest Industries is the underdog on our list. Great quality, smooth installation, yet it’s not that famous on the internet for some reason, probably because it’s somehow overpriced.
Lucky for us and you, their website discloses a lot of details about how they manufacture their lower parts. The parts are all made by BCM, a manufacturer that you somehow don’t need to question the quality of their firearm accessories. Hence, the price.
The manufacturers of this kit boast of their BCM trigger and hammer, where they’re carefully made under mil-specs. Moreover, they go through an intensive heat treatment process to achieve structure alignment and enhance their wear resistance.
To improve the smoothness of the trigger, there’s a nickel coating applied to it, which also boosts its resistance to rust, corrosion, and discoloration.
TacFire AR-15 USA Made Lower Parts Kit
Now, if you’re looking for a lower parts kit that’ll give you a quick build whilst being cheap, then the TacFire LPK is your best bet.
TacFire has been in the business for ten years, providing tactical and firearm accessories at affordable prices, and their AR-15 LPK is no different. Overall, the kit performs well and comes polished in mint condition. Their best feature is their well-made trigger parts with an especially smooth pull and a short reset.
The kit features a Nato 16” forged barrel with a 1:8 twist. The right handguard is made of quality aluminum with multiple QD slots that are convenient for rail segments. Its only downside is that it has no special security features when mounting onto the barrel, which was disappointing to some reviewers. This could use some improvement.
Reviewers who bought this kit agreed that its installation was easy, and it fits nicely with ARs and PSA lowers. If anything, you need to make sure you’re oiling the parts well during their assembly.
We’ve said it before, but we can’t help but say it again, this is arguably the perfect kit for beginners, for it strikes a balance between quality, price, and ease of use exceptionally well.
Building the lower receiver of your rifle is an educational and rewarding experience that’ll teach you about the workings of your AR more than anything. Installing the AR-15 lower receiver parts kit should take less than two hours for beginners.
We didn’t include all popular brands like CMC Triggers or Strike Industries in this guide, but if you go with any of the options we provided you should be fine. Further customizations can be made as you progress
We strongly recommend you consider this list of tools needed for building a custom AR-15 from the ground up:
- Roll Pin Punches — 3/32″, 1/8″, and 5/32″
- Gunsmithing Hammer — Used with punches and to help install pins for hammer and trigger
- Needle Nose Pliers — Useful for dealing with tiny detents and springs
- Masking Tape — Good for covering the receivers finish to protect it from damage when hammering and using punches
- Knife / Razor — Useful for compressing the spring-loaded detent when installing the takedown pin
- Lubricant — For making pins slide with ease
- 3/16″ Allen Key — To install a pistol grip’s screw and washer
One last thing to consider. If you do not already possess a buffer tube or stock parts, then it might be a good idea to look at complete AR-15 rile lower build kits that include all the items you’re missing to finish the lower receiver.