Building an AR-15: A Guide to the Parts

Building an AR-15 is an exciting endeavor that allows you to customize your rifle according to your needs and preferences. In addition to being a fun task, it can help you learn more about the inner workings of a semi-auto rifle and get more for your money. Whether you are a seasoned gunsmith or a novice enthusiast eager to embark on your first build, this guide will walk you through some of the most important steps of building an AR-15 rifle. From the initial considerations to the essential parts categories, we will cover everything you need to know to create a personalized and reliable firearm.

Considerations Before Building an AR 15

Before we jump into the parts you need to build your AR-15, there are some important factors you need to consider. Regardless of your level of experience with guns or gunsmithing, these are important details that will dictate some of the process:

Firearm Laws

Familiarize yourself with federal, state, and local laws regarding firearm manufacturing and ownership. When setting out on a project like this, you want to make sure you’re compliant with all regulations and obtain any necessary permits or licenses before commencing your build.

Purpose

Determine the purpose of your AR-15 build. Whether it’s for target shooting, home defense, or competitive shooting, your intended use might influence the selection of some of your parts and accessories in your AR build.

Skill Level

Assess your skill level and comfort with the assembly process. If you’re a beginner, it’ll be easier to assemble your rifle using parts/components that are previously assembled. While this can vary depending on your comfort level and ambition, using complete uppers and lowers can make it easier for you to put together and customize your rifle with less risk of damaging or losing small parts. 

Essential Parts Categories for an AR-15 Rifle

Now that we’ve looked at some of the things to consider before starting an AR-15 build, it’s time to take a look at the parts themselves. While these can vary some based upon the type of rifle you’re building and the style you’re going for, every AR-15 needs these basic components to be a functional rifle.

AR-15 Lower Receivers

The AR-15 lower receiver serves as the foundation of your AR-15 build and houses the trigger group, magazine well, and pistol grip. It is regulated as the firearm’s serialized part, meaning it’s registered and must be purchased through a licensed dealer with the same legal processes required to purchase a full gun. While there are many different options out there for lower receivers, it’s important to get one that’s sturdy and high-quality to assure proper performance of your finished rifle. 

As previously mentioned, you have the option of getting a stripped lower receiver, which needs to be completed with things like the trigger assembly, mag release, bolt catch, buffer tube, grip, and stock. It provides more of a blank template for your build but requires more work since all of these pieces need to be added on during assembly.  

The alternative option is to buy a complete lower, which has all the previously mentioned parts already installed much of the time. Though all the parts can still be swapped out at any point during assembly or down the road, it provides you with the pieces you need to have a complete and operational lower. While the overall cost may be a little higher, remember that this keeps you from having to spend extra on a buffer tube, stock, trigger assembly, etc.

We’re going to look at a few receivers for each category, so you have some options to choose from when looking for a lower.

Aero Precision Enhanced complete Lower w/Magpul Grip and Stock

This Aero Precision Enhanced complete lower is a great example of a complete lower. It features a black anodized receiver that delivers great durability. Additionally, It features a Magpul STR adjustable stock and a Magpul grip.

Anderson Manufacturing Complete Milspec Lower Receiver

Another great option for your AR build, this Anderson Manufacturing complete lower is a milspec lower that’s built with durability in mind. It features more of a traditional M4-style stock and grip, and has a CNC machined aluminum receiver with an anodized finish. Since it’s milspec, it’s built for compatibility with other milspec AR parts.

Aero Precision Stripped Lower Receiver Gen 2

For those looking to start their build with a stripped lower receiver, this Aero Precision AR 15 lower is a great choice! It’s a sturdy build, with 7075-T6 anodized aluminum. It’s also multicaliber, allowing you to build an AR in the caliber you choose, rather than being relegated to only assembling a 5.56/.223 build (though keep in mind, your bolt carrier group and barrel will ultimately determine the caliber of your gun). It’s a great option for those looking to build a quality AR-15 without breaking the bank.

Spikes Tactical Punisher Stripped Lower Receiver

Another option for a stripped lower receiver, for those who want some additional flair, is this stripped lower from Spikes Tactical. It has the Punisher logo and color fill on the safety indicators. Speaking of these indicators, there’s an additional fire-mode spot for those that want to do a build with a binary trigger system. It also delivers great durability, featuring the same 7075-T6 aluminum and anodized finish of the Aero but with the additional features we described.

AR 15 Upper Receivers

The next part of the build we’re going to look at is the upper receiver. The upper receiver houses the bolt carrier group, charging handle, handguard, barrel, and gas system. It connects with the lower receiver to complete the AR-15 platform. Just like the lower receiver, the upper receiver’s quality and compatibility are vital for a properly functioning firearm. Additionally, like we mentioned previously about the lowers, you can either purchase a complete upper receiver or you can purchase the stripped upper and individual parts if you want to do the full assembly. We’ll take a look at a few of our top options to help you decide which is best for you.

Aero Precision M4E1 Complete Upper 5.56 NATO w/M-LOK Handguard

For those that are interested in using a complete upper, this Aero Precision AR 15 upper is a great option! It features a 16-inch M4 carbine-style barrel, a carbine-length gas system, and a M-LOK handguard with top Picatinny rail sections for sights, an optic, or additional accessories. The barrel also comes threaded with a standard A2 flash hider. Additionally, keep in mind that any of these parts can be easily swapped for extra levels of customization. However, this option still requires the purchasing of a bolt carrier group and charging handle, which we’ll look at later.

Spikes Tactical Complete Upper 5.56 NATO

If you’re looking for a top-of-the-line complete upper that can be easily customized and accessorized, this Spikes Tactical upper might be the best option for you! While it has a higher price than the Aero Precision, it features a full top Picatinny rail and additional rails at the 3, 6, and 9 o’clock positions for easy accessorization. This upper also comes with a 16-inch barrel and a mid-length gas system. Also important to note, this upper features the charging handle and an M16 complete BCG (bolt carrier group), meaning you can easily drop it on a complete/completed lower and have a finished AR build.

Aero Precision M4E1 Threaded Stripped Upper Receiver

If you want to work off a stripped upper receiver, this Aero Precision stripped upper will serve you well. It features a solid aluminum build with the same black anodized finish that the lowers we covered had. It’s designed for a standard 5.56 NATO BCG.

AR 15 Bolt Carrier Group (BCG)

The BCG consists of the bolt, carrier, gas key, and firing pin. It facilitates the loading, firing, and extraction of rounds in the rifle. A high-quality BCG that matches your intended use and is compatible with the chosen barrel and caliber is essential for the reliable and consistent cycling of the firearm. This bolt carrier group will need to be in the same caliber as the upper and barrel to ensure compatibility and safety. Here are two options we like for a standard build:

Aero Precision Complete Bolt Carrier Group 5.56/.223 Remington

A solid bolt carrier group with everything you need already assembled, this Aero precision AR 15 bolt carrier group is a great choice! It’s made from machined 8620 steel with a black nitride finish for smooth and durable operation. 

Midwest Industries Bolt Carrier Group 5.56/.223 Remington

Another bolt carrier group from a solid brand, this Midwest Industries AR-15 bolt carrier group provides excellent performance and durability. This BCG is made of 9310 steel with heat treatment and a black nitride finish for maximum durability.

Additional Parts for AR-15 Lowers

Now we’re going to take a look at some of the parts you’ll need if you decide to start your build with a stripped lower. While this isn’t an exhaustive list, it does give you an idea of some of the things you’ll need to buy to complete your build.

CMC Triggers Drop-In Two-Stage Curved AR-15 Trigger

This CMC Trigger group is a great choice for your AR-15 build. It’s a two-stage trigger that provides around 2 lbs of pull weight with a positive reset. It comes assembled, which makes it easy to install in your rifle build. The durable steel construction makes it a trigger you can rely on in your AR-15 build.

Rise Armament RA-535 AR-Platform Single Stage Trigger

Another great choice for your AR build, we have this trigger group from Rise Armament. It provides you with a single-stage trigger with 3.50 lbs trigger pull. It provides a durable build with steel and aluminum construction and a flat trigger for those that prefer it to a curved trigger. It’s another great choice for an AR build!

Aero Precision Carbine Buffer Tube Kit

With any AR 15 build, you’ll need a buffer tube kit. This Aero Precision buffer tube kit is a great choice if you’re building an AR-15 with a carbine-length gas system. It provides Aero Precision quality with a Mil-Spec, 6-position aluminum buffer tube at an affordable price.

Magpul MOE AR Grip

This simple grip from Magpul is a great standard grip for an AR build. It’s affordable while maintaining the Magpul reputation as a quality firearm part. We also have the Magpul MOE Grip in FDE and the Magpul MOE Grip in OD Green for those that prefer them.

Magpul MOE SL AR 15 Stock

This Magpul MOE SL Carbine stock is a great choice for any AR-15 build. It’s lightweight and features a rubber buttpad for extra comfort and recoil absorption. Its OAL of 7.2” makes it a great moderate size for carbine builds as well as rifle builds. It also multiple mounting points so you can easily attach a sling. Like the grip, we have them available in FDE finish and OD green finish as well.

Rise Armament AR-15 Lower Parts Kit

Last but not least for lower parts, we have this AR 15 lower parts kit from Rise Armament! This kit includes your mag catch, safety selector, bolt catch, and the pins and springs you need to assemble your lower. This kit, or a similar one, is a necessity for anyone buying a stripped lower and customizing the build.

Additional Parts for AR-15 Uppers

Now that we’ve covered everything you could or will need for a lower, we’re going to take a look the parts you’ll need to customize a stripped upper receiver. Again, this isn’t an exhaustive list. It features a few of our top picks to give you an idea of the parts you’ll need.

Ballistic Advantage Modern Series AR-15 Barrel 16” 5.56 NATO

If you’re looking for a standard AR-15 barrel that’ll stand up to the pressure of regular use, check out this Ballistic Advantage AR 15 barrel. It’s a 4150 chrome moly vanadium barrel that’s made to be a 16” M4 carbine length. It features a standard 1:7 twist rate and a 1/2×28 threaded muzzle. The Barrel has a 0.750” gas block diameter and is designed for a carbine length gas system. It’s HP and MPI tested and has a black finish.

Ballistic Advantage Premium Black Series AR 15 Barrel 16” .223 Wylde

This AR 15 barrel from Ballistic Advantage is another great choice for anyone looking to build or customize their rifle. While it’s still a 16” barrel, it’s chambered in .223 Wylde, meaning it can handle .223 Wylde, .223 Remington, and 5.56 NATO without issue. This particular model has a .750 gas block diameter and is built for a mid-length gas system. It has a 1:8 twist rate and a 1/2×28 threaded muzzle. It also delivers durability, with a hardened 416R stainless steel build and a QPQ corrosion-resistant finish.

Aero Precision Low Profile Gas Block .750” for AR-15

This Aero Precision gas block is a great choice for anyone whose build has a barrel with a .750” outer diameter. It’s made of steel with a black nitride finish, and has a low profile so it can fit more easily with a variety of handguards. However, the roll pin is not included.

CMC Triggers Corp Internal Bore Low Profile Gas Block .750”

Another great option for those in need of a gas block, this CMC Triggers low profile AR-15 gas block is excellent. It’s machined from durable 17-4PH stainless steel and fits on .750” barrels inside most free-float handguards. It includes the hardware you need to attach it to your barrel. The gas block works with CMC Triggers AR-15 nitride gas tubes and standard Milspec gas tubes as well.

Aero Precision Mid-Length Gas Tube

If you’re putting together your AR from scratch, you know you’ll need a gas tube. For those that are, this Aero Precision gas tube is a great choice. This tube is a stainless steel tube for a mid-length gas system, but we have a full selection of Aero Precision gas tubes that’ll meet your needs regardless of gas system length.

Aero Precision Enhanced 15” Handguard 

If you’re looking for a sleek handguard for your AR-15 build, check out this Aero Precision handguard. It’s a free float design with a full-length Picatinny top rail and M-LOK slots for easy customization. In addition to this, it has QD sockets for sling attachment, side milling for added grip, and compatibility with low profile gas blocks. Consider it for your build today.

Midwest Industries 15” Slimline AR 15 Handguard

Another great option, especially if you’re looking to get additional hardware, is this free floating Midwest Industries 15” Slimline handguard. It’s made of aluminum with a black anodized hard coat. Additionally, it comes with a barrel nut, wrench, torque plate, additional Picatinny rain, and hex keys to help you with your build.

Midwest Industries 15” Slimline AR 15 Handguard

Last but not last, there’s the charging handle. While there are a lot of options out there, this Radian Raptor-SD ambidextrous charging handle is a great choice for your build. It’s also made out of aluminum with an anodized finish and is designed to provide quick and easy charging of the gun. It’s compatible with most AR15/M16 pattern rifles.

Building your AR-15

Building an AR-15 rifle allows you to create a firearm tailored to your specific needs and preferences. While it may not be as easy as getting one preassembled, the level of customization that’s possible in building it yourself makes it a fun and rewarding journey. While this wasn’t a full guide to shopping for parts and assembling your rifle, we hope that it helped provide some inspiration for your next build or customization! Don’t forget to check out GrabAGun for all your future gun needs!

Remember to abide by all legal requirements and exercise caution during assembly. With careful planning and attention to detail, you’ll soon have a reliable, customized AR-15 that embodies your shooting style and passion. Happy building!