Rock River Arms LAR-15 outdoors

Best AR-15 Build Kits

Are you currently looking to put together your own AR-15 with a build kit? If so, you’ve come to the right place.

Best Lower Parts Kit: Geissele Automatics Lower Parts Kit

Geissele Automatics Lower Parts Kit

The Geissele Automatics Lower Parts kit comes with nearly everything that you need to complete the lower receiver of your AR-15. The parts are built out of a very durable and rust resistant stainless steel material to mil-spec standards, meaning that they should easily last you for a lifetime or longer.

See on Brownells

Best Upper Parts Kit: Aero Precision Upper Parts Kit

Aero Precision Upper Parts Kit

The Aero Precision Upper Parts kit includes most of the parts that you need to fit in the upper receiver of your AR-15. Built to mil-spec standards, each of the components are constructed out of tough 7075-T6 aluminum for excellent durability.

See on Brownells

Best Receiver Set: Nemo AR-15 Battle Light Receiver Set

Nemo AR-15 Battle Light Receiver Set

The Nemo AR-15 Battle Light Receiver kit is constructed out of tough 7075-T6 aluminum with a hard coat anodized finish for excellent rust and corrosion resistance. It comes ready to use with the Geissele lower parts and Aero Precision upper parts kits.

See on Brownells

The AR-15 has long been a very popular rifle, and for more reasons than one: it’s very modular, customizable, accurate, reliable, and ergonomic. The fact that you can swap parts to easily customize your weapon as you see fit alone is good enough reason to own an AR-15.

But besides customizing an existing AR-15, you can also build your own unique AR-15 from the ground up by buying all the parts individually. Alternatively, you can save money by just buying build kits instead.

In this guide, we’ll discuss the pieces you need to put together an AR-15 and what to look for in a parts kit. Then, we’ll discuss our choices for an upper parts kit, lower parts kit, and a receiver set.

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Why Build Your Own AR-15?

Why build your own AR-15 from the ground up rather than just buying one off the shelf? The answer is simple: if you want your AR-15 to be truly your own and only use parts that you have pre-selected, you need to build your own AR-15.

Furthermore, building an AR-15 from the ground up will give you a clear understanding of how the AR-15 works on the inside and out. You will become totally familiar with the weapon and all of the individual parts that are involved with making one.

It’s the same logic as to why you should build a survival kit with individual survival items rather than just buying a pre-packaged survival kit: you become totally familiar with the contents of your kit, which means that your kit can serve you better. The same goes for your AR-15, which honestly is not as complicated of a rifle as you may have initially thought.

In other words, even though there will be challenges along the way, putting together your own AR-15 should not be as difficult as you may have been anticipating. If anything, building your own AR-15 from parts kits should be a fun and rewarding experience.

Aside from its ease of customization, there are many more reasons to own an AR-15 as well. But perhaps the biggest reason of all is the fact that the AR-15 is one of the most versatile weapons on the face of the planet. It can be used for virtually anything you need a rifle for, from long distance shooting to hunting to tactical uses to home defense, and it can offer all of these things in a platform that is ergonomic and very easy-to-shoot.

In the standard 5.56 caliber, the AR-15 can drop medium sized game such as deer, antelope, or wild boar (for larger game such as elk, consider a larger caliber such as the .308 Winchester or 6.5 Creedmoor). The 5.56 round offers suitable stopping power for self-defense, and this combined with the low recoil of the AR-15 make it a solid choice for home defense as well. If you are looking for smaller calibers there are .22LR conversion kits available.

If anything, the AR-15 can be a more valuable home defense weapon than either a shotgun or a handgun. It offers superior range to both weapons, less recoil than a shotgun, and greater stopping power than a pistol. The fact that it offers twenty to thirty rounds in the magazine on average means that it is a suitable defensive weapon against multiple attackers as well. Speaking of recoil, a great way to lower the kickback is to attach a good AR-15 muzzle brake to your rifle.

All in all, the AR-15 is a solid choice for a rifle. There’s a reason why it’s the bestselling centerfire rifle today and known as “America’s rifle.” By assembling your own AR-15 from a parts kit or build kit, you can create an AR-15 that’s truly yours and customized to your liking.

In the next section, we’ll outline and discuss the primary pieces that you need to put an AR-15 together.

Also read: Best AR-15 Side Charging Uppers

What Are The Pieces You Need?

Here are the individual pieces that you will need to put together your AR-15:

Upper Receiver and Lower Receiver

Every AR-15 can be divided into the upper receiver and lower receiver. These are the central components of the rifle that house the other parts and springs.

When putting together your AR-15 from a build kit or parts kit, you can buy what are called “receiver sets” or upper receivers and lower receivers sold together as a single unit. You will then need to buy an upper parts kit and lower parts kit for the remaining pieces that you can install.


The grip is what your shooting hand grasps on to when firing or holding your AR-15. However, most parts kits will not ship with a grip, which means that you will need to purchase on separately. It’s very important than any grip you get is very comfortable and ergonomic, so you actually enjoy shooting your AR-15.

Also be sure to research the legal requirements when it comes to grip. Some states and jurisdictions, such as California, do not allow pistol grips but do allow AR-15 featureless grips.

Hand Guard

The hand guard of an AR-15 is what covers the gas tube and the barrel. It also permits you to add accessories to it, such as sling swivels, forward grips, lasers, sights, and so on.

However, hand guards are also usually not included with a parts kit or build kit, so you will need to add these yourself by buying them separately. As a golden rule, go with a free floating hand guard versus the more traditional two piece design. Free floating hand guards genuinely do offer a slight increase in accuracy, and also have more space for adding accessories via their mil-spec Picatinny M1913 rails.

The size of hand guard you need is also dependent on the length of barrel you have, which would include rifle, mid-length, carbine, or pistol. Speaking of the barrel…


The barrel is another integral part of the AR-15 that is usually not sold in an upper (or lower) parts kit. Therefore, it’s another part that you will need to buy separately, fortunately for you we have a buying guide for AR-15 barrels as well.

The main barrel lengths are rifle (20 inch), mid-length (18 inches), carbine (16 inches) or pistol (anything under 16 inches). The longer your barrel, the longer and more unwieldy your rifle will be, but it will also have greater bullet velocity and therefore better accuracy at longer ranges. For every added inch to your barrel, you can expect the barrel to add approximately two hundred FPS (feet per second) on average to the velocity of your rounds.

Your barrel should come chrome lined in order to make it more durable and add longevity. A chrome lined barrel will on average have an additional 5,000 round service life over a barrel that is not chrome lined.

Also pay close attention to the twist rate of your barrel, or the number of inches a bullet fires in order to make one rotation. The lower the twist rate, the faster the bullet is traveling and therefore the more stable it will be, which also translates to added accuracy at longer ranges.

Trigger and Fire Control Group

Triggers and fire control groups are usually not sold as part of lower AR-15 parts kits because they are what allow the rifle to fire and therefore need to go through an FFL in order to be legal to buy.

If you go with mil-spec parts and a mil-spec upper and lower, then you can go with a mil-spec AR-15 trigger and fire control group as you know they will be compatible. Most mil-spec triggers are actually quite crisp and satisfying to shoot.

The fire control group refers to all of the parts required to fire the rifle, including the trigger, sear, hammer, disconnector, and springs.


There are two primary kinds of stocks to the AR-15: collapsible and fixed stock. Fixed stocks are more durable, sturdy, and in general are a superior choice for long range precision shooting. However, they are not as adaptable and not the best choice for self-defense situations in tight environments or conditions.

Folding stocks can reduce the profile of your AR-15 and are therefore a better choice for most close quarters tactical uses or for transport.

Charging Handle

The charging handle to the AR-15 moves the bolt, striker, and hammer into the ready position so that the weapon can chamber a round and fire. If you are left handed, you’ll need either a left handed charging handle or an ambidextrous model. We have a guide on he best left handed AR-15 uppers, if you are interested in that.

Gas System

Finally, when buying any build kit or parts kit, you will need to decide between a gas impingement or a gas piston system. Gas impingement systems are far more common with parts kits and will therefore likely be compatible with the individual parts kit that you select.

More AR-15 content: The best Magwell Grips for your rifle

Buyer’s Guide For The Best AR-15 Build Kits

These are the most important factors to consider when looking for a new build kit for your AR-15:


Remember that the primary reason to buy a build kit or parts kit rather than just purchasing all of the parts separately is to save money. Therefore, actually take the time to calculate how much it would cost to buy each of the parts in a kit separately and then weigh the total against what the kit itself costs. Always go with the cheaper option in regard to the same parts.

What Does It Come With?

Not all parts kits or build kits for ARs come with everything you need. If you get a lower parts kit, for example, chances are good it comes with almost everything you need for your lower receiver, but there will still be a few pieces missing that you will need to buy separately (such as the fire control group).

Durability of Components

Make sure that the components in your build kit are each well-made and durable, such as stainless steel or 7075-T6 aluminum. They should also be built to mil-spec tolerances, which means that they will be compatible with other mil-spec parts.

Easy to Install

The parts in your parts kit should not require the aid of a gunsmith to install. You should be able to easily fit the components into a mil-spec grade upper or lower receiver easily.

Read also: Our buying guide on AR-15 BCGs

The 4 Best AR-15 Build Kits For 2020

Now that we’ve covered what to look for in a build kit, here are top three choices for a kit:

Geissele Automatics Lower Parts Kit

Geissele Automatics Lower Parts Kit

For a lower parts kits, the Geissele Automatics Lower Parts kit represents a solid choice. As a lower parts kit, the pieces in this kit will fit in well with your lower receiver. The parts included are the buffer tube, safety assembly, bolt catch, bolt catch plunger, mag release, mag release spring, spring and roll pin, and the trigger assembly. The only parts missing are the pistol grip and the fire control group, which you will need to purchase and install separately.

Each component included in the Geissele is built out of high quality stainless steel, which offers far greater durability and rust and corrosion resistance than the comparable MIM (metal injection molding parts). Each part in this kit is also built to mil-spec standards.

All in all, the Geissele Automatics Lower Parts kit offers you nearly everything that you need to complete the lower receiver for your AR-15. All of the parts are built out of high quality stainless steel, making them very durable and rust resistant, and are also built to mil-spec standards.

See on Brownells

  • Built to mil-spec standards
  • Includes all parts you need to complete your lower receiver
  • Built out of durable stainless steel materials
  • Trigger assembly is a little bit gritty

Aero Precision Upper Parts Kit

Aero Precision Upper Parts Kit

The Aero Precision Upper Parts Kit is our recommendation for parts for the upper receiver of your AR-15. The parts included in this kit are the forward assist assembly, spring and roll pin, ejection porn assembly, cover door, cover spring, and cover rod with C-clip.

This parts kit is built to mil-spec standards and are constructed out of durable 7075-T6 aluminum with a nitride finish for excellent longevity and corrosion resistance. The parts are all designed to be drop-in, meaning that they do not require specialized tools or the aid of a gunsmith, and making this kit a solid choice for first time builders.

Overall, the Aero Precision Upper Parts kit is an excellent parts kits for the upper receiver of your AR-15. The mil-spec grade parts are all built out of durable 7075-T6 aluminum and are designed to be as easy to fit in as possible.

See on Brownells

  • Very easy to install
  • Good pick for first time builders
  • Built to mil-spec standards
  • Roll pin hard to secure

Nemo AR-15 Battle Light Receiver Set

Nemo AR-15 Battle Light Receiver Set

You’ll next need a Receiver Set for your AR-15, and one of the best options is the Nemo AR-15 Battle Light Receiver Set. This receiver set is built out of very durable 7075-T6 aluminum and comes with lightening cuts in different areas in order to reduce the weight. It has M4-style feed ramps machined into the upper in order to ensure more reliable feeding.

The entire set is finished in a hard coat anodized finish, and the integrated tension screw helps ensure as tight of a fit as possible. Meanwhile, the trigger guard has been enlarged in order to accommodate a gloved finger.

Nemo AR-15 Battle Light Receiver Set side

The Nemo AR-15 Battle Light Receiver Set is built to mil-spec standards and constructed out of tough 7075-T6 aluminum with an equally tough mil-spec finish. This is an excellent receiver set to use in conjunction with the Geissele Lower Parts kit and Aero Precision Upper Parts kit like we just discussed.

See on Brownells

  • Rear tension screw ensures a tight fit
  • Built to mil-spec standards
  • Constructed out of durable 7075-T6 aluminum
  • Has a very durable hard coat anodized finish
  • None

CMMG AR-15 Lower Gunbuilder’s Parts Kit

CMMG AR-15 Lower Gunbuilder's Parts Kit

The CMMG AR-15 Lower Gunbuilder’s Parts Kit is aimed at providing almost everything that you need to complete your AR-15 lower receiver. Built out of 7075 aluminum, these parts do not require the services of a gunsmith to install and are compatible with any mil-spec grade AR-15 lower.

The parts included in this kit include the safety selector, magazine catch, magazine release, pin detent, spring, takedown pin, buffer retainer, bolt catch, and all the additional pins and springs needed to complete your lower. However, it lacks trigger, guard, and grip, so you will need to buy those items separately.

All in all, the CMMG AR-15 Lower Gunbuilder’s Parts Kit is an excellent choice for a parts kit if you need to complete the lower receiver to your mil-spec grade AR-15. Even though it lacks the trigger guard and grip, it comes with everything else you need for your lower and does not require the services of a gunsmith either.

See on Palmetto State Armory

  • No fitting from a gunsmith are necessary
  • Very easy to install
  • Comes with the pins necessary to complete a stripped lower
  • Compatible with all mil-spec AR-15 lowers
  • Built out of high quality 7075 aluminum
  • Lacks trigger, trigger guard, and trigger grip

Wrap Up

The three build kits that we have covered here today (lower parts kit, upper receiver kit, and receiver set) will all be necessary in order to help put your new AR-15 together. Alternatively, you can look for more parts kits by using the buyer’s guide that we discussed earlier as well.

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