Learn How to Build an AR15

An AR 15 rifle is lightweight, semi-automatic, and heavily based on the ArmaLite "AR15" design, the scaled-down version of Eugene Stoner's original AR10 design. Besides being incredibly flexible and easy to use, building one has been described to be straightforward and relatively easy, making it suitable for individuals without prior experience. Unless you're installing barrels and rail systems, learning how to build an AR15 is simple. All you'll need to do is get some "basic tools", like a philipps or a flat head screwdriver, and follow simple instructions. 

Typical AR15s are rifles with a 16-inch barrel, often chambered in 5.56/.223, which is the gold standard for most rifles. The best part is, you can always customize these later. Additionally, you don't need to worry about the legal aspects of building a AR 15 since the Gun Control Act and Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) approve building a gun from scraps and parts — as long as you can otherwise legally own a firearm. Tactical gear heads are very enthusiastic about building their own AR15.

Depending on the instructions, the tools you'll need to use to assemble everything from barrels to gas blocks and rail systems vary, but it's best to take a "simpler" approach, which is what this guide will teach you today. 

Build Your Own AR15 with Custom Parts

Since most firearm builders choose to buy a barreled upper assembly, the only part you need to construct when you build your own AR15 with custom parts is installing the lower parts kit into its stripped lower receiver and adding its buffer tube and buttstock. It's a relatively simple process requiring minimal knowledge and "basic" tools — and you can complete the whole project in two hours once you've got all the parts for your AR 15.

The most time-consuming part of making a AR 15 at home isn't the build itself, but the time it takes to pick out individual and custom parts alongside configuration that best suits your preferences. 

There are parts of an AR15 that are tuned to a particular performance characteristic. You can design a customized precision sniper rifle, if you really want to. You can even fine tune your adjustable receiver link, for easier disassembly. 

After you make this decision, you should be able to know what upper receiver and barrel you'll need.  

That said, here are the different kinds of stripped upper receivers: 

AR15 A1

The AR 15 A1 needs a fixed carry handle and shell deflector, all while requiring an ejection port cover, forward assist, and A1 sight assembly that enables flexible windage adjustment. It's the best upper for building "retro" civilian models of the classic M-16 rifle from the Vietnam era. 

AR15 A2

The AR 15 A2 comes with a fixed carry handle and shell deflector. It needs the forward assist, ejection port cover, and A2 sight assembly — allowing for flexible windage or elevation adjustments. It's a popular upper to utilize when building rifles intended for shooting matches. 

AR15 A3

The AR 15 A3 comes with a Flattop with a Picatinny rail and shell deflector. It needs the installation of the ejection port cover and the forward assist assembly. It's the current military upper, often used to create civilian copies of the infamous M4, a carbine with a 16-inch barrel, or M16 A4, a rifle with a 20-inch barrel. 

Additionally, the A3 is an excellent model for making Varmint and Target carbines or rifles since all optics are mountable on a Flattop. 

AR15 Flattop

The AR 15 Flattop has multiple configurations for its upper receiver with different heights of Picatinny rails for its mounting scope. The Flattop typically doesn't accommodate the forward assist assembly or ejection port cover assembly. 

This particular build for an AR 15 is excellent for creating a Target carbine or rifle Varmint since you can mount any optics on a Flattop. 


Finally, before building your very own AR-15 with custom parts, ensure to check if it's legal to make one at home in your location. Although it's primarily legal in several states, it has its restrictions. The ATF has long held that it's legal for residents to build this particular rifle at home for personal use. 

The AR15 Parts List

Regardless of the configuration and caliber, you're going for — you can separate a AR 15 rifle into two components: the upper receiver assembly and the lower assembly. That said, here is the AR15 parts list you need to prepare for both systems: 

AR-15 Upper Parts List

To build a "mil-spec" AR 15 rifle, you need to have the right parts on hand, and it's best to begin with the business end — the upper receiver. Here are the required upper receiver parts when it comes to building a AR 15 upper parts list: 

Stripped Upper

The stripped upper is considered the housing of bolt carrier groups containing the barrel extension. Meanwhile, the external threads are where the barrel can mount itself to through a high-torque barrel nut. 

Most stripped uppers are made from 7075-T6 aluminum. When looking for a quality stripped upper, you'll want an upper receiver with M4 feed ramps, ensuring the loaded rounds won't malfunction. But, stripped uppers automatically come with these feed ramps. 

A typically stripped upper comes with a forward assist, used to force BCG into the battery when dirty. If you're looking to make a AR 15 with a light and compact build, you can purchase a "slick-side" upper with none of those features. 

Finally, most modern uppers come with a Picatinny rail for attaching iron sights or optics. Upper receivers can mimic the design of conventional M16 rifles, sporting an integrated carry handle and rear sight. 


In aAR 15 build, the barrel is one of the most crucial pieces to have in your uppers kit. It can help you determine what ammunition to shoot, how far it can go, and how accurate your overall firearm is. 

Here are the specifications you need to keep in mind when choosing a barrel:

  • Length 

The appropriate barrel length for a rifle's barrel is 16 inches, the optimized length for .223 Remington cartridges and 5.56 NATO cartridges. Buying a shorter barrel means you need to reconfigure your AR 15 as an AR pistol without a stock. 

However, these two cartridges commonly used for building AR 15 rifles don't offer distinct benefits. 

  • Profile

AR 15 barrels are often shaped in various profiles, increasing or reducing weight — aiding in the gun's overall accuracy. The most commonly used profile for building AR 15 rifles is the M4 or Government profile, a perfect balance in weight, accuracy, and ruggedness. Meanwhile, bull barrels can help improve accuracy and heat dissipation when rapid firing, while lightweight or a pencil profile can help reduce weight. 

  • Material

Most modern AR 15 barrels are made from the material 4140 Chromoly, 4150 CMV, and stainless steel, with the most common one being 416R stainless steel. The 4140 material is cheaper but a lot softer than the others. However, the "mil-spec" of a stainless barrel is made from 4150 CMV, providing better accuracy — at a higher price. 

  • Twist Rate

This factor refers to the number of inches the rifling goes through before completing a whole rotation. For instance, a barrel with a twist rate ratio of 1:7 means the rifling can rotate once every 7 inches. The popular 5.56 NATO and .223 Remington cartridges are most sold in 55-train and 520grain loads, favoring a 1:8 twist rate, which is solid. However, if you're looking to achieve better accuracy and range, the standard 1:7 twist rate ratio is ideal. 

  • Gas Port Length

An AR 15 rifle utilizes a direct-impingement gas system, bringing gas back into the rifle's upper receiver through a gas block or gas tube, cycling the bolt.  Multiple gas tube port lengths are compatible with the AR 15 model, including pistol, carbine, mid-length, and full rifle-length. 

AR pistol-length units work best with low-power cartridges and specialize in creating short-barrel or "pistol builds." 

Meanwhile, the carbine and mid-length units are the best choices for the .223 and 5.56 cartridges in a 16-inch barrel. Finally, rifle-length gas systems are perfect for long barrels of at least 20 inches and more. 

  • Barrel Threads and Muzzle Devices

Nearly every 5.56 NATO and .223 Remington cartridge barrels come with 1/2 x 28" barrel threads, which is the universal standard for all .22-caliber muzzle devices. The most common is the conventional A2 birdcage flash hider, typically involved on assembled uppers, performing decently. 

  • Barrel Coating and Treatment 

Stainless barrels are often untreated and feature no coating, while 4140 Chromoly or 4150 CMV barrels sport a lower-quality phosphate coating or expensive nitride coating inside and out. The most preferred among expert builders are barrels with nitride coating and treatment. It improves the barrel's quality and protects the rifling against lead deterioration or corrosion while improving overall accuracy. 

Gas System

An upper receiver's gas system consists of two simple components: the gas block, which sits on the barrel, capturing excess gas, and the gas tube, responsible for connecting the gas block to the upper receiver and the bolt carrier key inside it. 

Here are the right gas system lengths: 

  • AR15 Pistol

It has a gas system length of 4 inches and is meant for 10-inch barrels or less. 

  • Carbine

The carbine gas system comes at 7 inches and is meant for barrels between 10 inches to 18 inches. 

  • Mid-Length AR 15

9 inches, and meant for barrels between 14 inches and 20 inches. 

  • Rifle Length

A full rifle gas system length is 12 inches and is compatible with barrels of at least 20 inches or longer. 

When it comes to gas block types, the most common one is the low-profile block. A low-profile gas block usually fits beneath the upper receiver handguard, enabling longer handguards with multiple mounting points and rails attached over the barrel. Meanwhile, the conventional or "old style" gas block containing the front sight post is considered the M16 gas block, requiring a two-piece handguard to be installed with it. 

Although you can't change everything, you can adjust many gas blocks, providing more or less gas to the bolt carrier. These are usually used on low-powered cartridges and suppressed firearms shooting subsonic ammo. However, they're not required for the typical 16-inch barreled rifle that shoots 5.56 or .223.

Additionally, a part of the upper receiver system is the gas tube. Gas tubes can be measured with the gas system lengths mentioned earlier with the help of a gas tube alignment tool. Each gas tube has the same diameter, so the "length" is the only thing you need to consider. Most gas tubes are made from steel, making them sturdy and reliable. 


The upper receiver comes with a handguard that'll determine how heavy your AR 15 will be and what kind of mounting system you'll need to secure attachments, ranging from iron sights to other accessories. The mounting or rail systems of a handguard consist of several attachment systems, with the Picatinny rail being the most popular one among experienced AR builders. However, M-Lok and Keymod are also excellent attachment system choices. 

An upper receiver handguard can be free-floating or two-pieced. A free-float handguard is designed to "float" over the upper receiver's barrel and don't contact any part of it. It has a low-profile gas block underneath it, naturally increasing accuracy, and it usually attaches via the inner barrel retainer nut and upper receiver. Meanwhile, two-piece handguards need the M-16 rifle-style front sight post and gas block to be more rugged. 

Bolt Carrier Group

Going back to the upper receiver, the bolt carrier group (BGC) usually works with the AR-15's hammer and magazine, while the lower receiver uses the chamber, fire, and cycle rounds. All bolt carrier groups are generally fitted for 5.56 to .223-chambered AR 15 rifles — and they come in different profiles, including commercial or lightweight, and M16. 

An M16 won't make your AR 15 fully automatic, but these bolts are generally heavier and sturdier, reducing felt recoil for more accurate shots. 

In contrast, commercial or lightweight bolt carriers possess less material in their bodies, providing an overall "lighter" solution. A BGC is usually coated with nitride or phosphate, while higher-end ones use chrome or nickel treatments, providing natural lubrication, making them look more appealing. 

By now, you should have a better understanding of all the components needed to purchase a quality and appropriately configured upper receiver assembly and lower receiver assembly — making your DIY gun building journey easier.

AR-15 Lower Parts List

The lower receiver assembly is easier to handle than the upper receiver assembly, and the most complex components are the parts kit and trigger assembly. When dealing with the lower receiver assembly, here are the things every lower parts list should have: 

Stripped Lower Receiver

Although it doesn't look as threatening, in the perception of the ATF, this is a firearm, meaning no trigger, barrel, or other lower receiver parts are needed for it to be considered as such, legally. Like the stripped upper receiver, the stripped lower receiver is simple, typically made from aluminum, promising a relatively lighter weight carbon fiber and polymer lower receivers. Additionally, like the stripped upper receiver, most lower receivers come with an anodized finish in custom colors. 

The stripped lower receivers are fabricated and are often ready for the trigger hammer and lower part kits to be installed. That's why the ATF considers the lower receiver as an official gun. 

AR 15 builders have recently used receiver blanks for their builds, typically called the 80 percent lower receiver. Each unit requires fabrication, such as drilling the kit's gas hole or cutting the cavity part of the kits, making the lower receiver more functional.  

Although it's legal to do under federal law, some "basic tools" and machining knowledge regarding upper receiver and lower receiver assembly are required. 

Lower Parts Kit

The lower parts kit of the lower receiver ensures every function for a AR 15 build is going smoothly. However, keep in mind that some parts kits won't come with parts like a pistol group, so make sure to check the lower receiver parts kits before buying one. That's why virtually every lower parts kit needs to use the same components — ranging from steel to cast-aluminum lower. 

Mil-spec kits utilize a simple "single-stage" trigger, while more expensive lower parts kits offer adjustable triggers that can help with the gun's overall accuracy. Most lower parts kits contain the following items: 

  • Bolt catch

  • Buffer retainer, spring

  • Small ball-peen hammer

  • Magazine catch

  • Needle nose pliers 

  • Front sight block

  • Torque wrench

  • Upper vice block clamp

  • Pistol grip lock washer and grip screw

  • Pivot pin, detent, and spring

  • Bolt cam pin

  • Trigger, trigger guard, guard roll pin, and spring 

  • Roll pin installation tool 

Buffer Tube, Spring, and Buffer

The standard Carbine buffer tube and recoil spring are the "gold standard: for every AR 15 build chambered in 5.56 and .223 cartridges. Most buffer tube housing units are made from forged aluminum, with Mil-spec tubes using forged aluminum — and commercial buffer tubes from billet aluminum. Meanwhile, recoil springs are virtually the same for AR 15 rifle builds. However, you can also opt for custom springs for specialty applications. 

The buffer weight acts as the counter-weight to the bolt carrier group cycling back and forth — where the buffer absorbs recoil and pushes the BCG back into the lower receiver through the recoil spring. 

When it comes to buffer tubes, stick with a Carbine buffer for standard 16-inch barreled rifles, reducing recoil and maintaining reliable cycling ammunition. Finally, the longer your gas tube is, the less energy will be transferred to the bolt and buffer tubes. 

Essential Parts of an AR15 That You Don't Need to Buy Separately

The AR15 is a deadly weapon, and depending on your location, there are rules on buying this guy. It might also not be possible to buy all the parts in-store or online. However, if you can buy a whole gun, you can customize it according to your preference. 

there are six "key" elements or essential parts of an AR15, including the lower receiver, upper receiver, length of its gas systems, barrel, handguard, and bolt carrier group. 

There are four variations on the lower receiver, including the billet aluminum lower, cast aluminum lower, forged aluminum lower, and polymer lower. The most commonly used among them is the polymer variant, thanks to its lighter weight. 

However, many people assume it to be weaker at the front hinge pin and can damage the buffer tube threading, which is false. However, if you're on a tight budget, choosing cast aluminum lowers is also acceptable since they're cheaper and can be made at home. 

Meanwhile, the uppers are more comprehensive than the lower, boasting two systems in AR-15s: the direct impingement system and piston system. The ideal AR 15 model comes with the "direct impingement system." 

It's a gas-operated system where high-pressure gas from your chosen cartridge is being fired and is used in powering mechanisms excreting your spent casings and chamber. Meanwhile, the less common piston system is fixed to a bolt group, circulating through the entire operating cycle. 

Regarding gas system length, choosing the right one is integral when making an AR 15 rifle since it determines the level of action you're going to achieve with the firearm. The ammunition still needs to be inside the barrel when the gas hits the bolt carrier to achieve enough force to cycle this action. 

Since your ammo will be in constant movement, you need to have an appropriate barrel length remaining to let the bullet leave the muzzle after a certain amount of gas has been transferred to the BCG. 

However, if you have too much barrel, the BCG will have too much gas, resulting in excess leaking, damaging the functionality of your AR 15. In contrast, if you use a too short barrel, it won't have enough force to unlock the bolt, and if this is the case, you'll need to place its gas port closer to the muzzle. To get the most out of your AR 15, make sure to budget for the barrel since it's one of the more vital parts. 

Sourcing AR15 Components

When it comes to sourcing AR15 components, make sure to choose the highest quality and most functional ones from reliable brands, and here's a rundown of everything you need to know tick off the list when building a AR 15 rifle: 

  • Stripped Lower Receiver

It's the serial numbered part of the AR 15, and buying one works the same way as purchasing a completed gun. It must ship to an FFL dealer and pass a background check under federal law. 

  • Lower Parts Kit

You'll need 31 parts to assemble the "stripped lower," ranging from the trigger, bolt catch, springs to takedown pins. 

  • Pistol Grip

A "basic" pistol grip is included in the lower parts kit, but aftermarket grips usually have a better "hand" fit.

  • The Fire Control Group

Consists of hammer, hammer spring, trigger, trigger spring, disconnector, disconnector spring, and fire control pins found in lower parts kits.

  • BGC

It holds and moves the bolt, resetting the hammer. This component includes a bolt carrier, firing pin, complete bolt, carrier pin, and gas key. 

  • Buffer

This slows down the AR-15's bolt, absorbing recoil and reducing the wear on the gun.

  • Barrel

There are several barrel lengths to choose from, alongside twists and calibers. 

  • Gas Block

This directs gasses from the barrel to the gas tube and into the rifle's receiver — making way to another round. 

  • Gas Tube

These vary in length, ranging from rifle to pistol lengths. 

  • Upper Receiver

It holds the forward assist spring and the forward assist pin, ejection port cover pin, charging handle, barrel, and BGC. You can purchase an upper receiver assembly with a bolt carrier assembly with barrels. 

  • Upper Receiver Parts Kit

This includes ejection port doors, springs, forward assist parts, and charging handles but doesn't come with bolts or carriers. 

  • Charging Handle

It pulls the bolt carrier back, aiding in clearing malfunctions. 

  • Handguards

They protect the shooter's hands from burning on a scorching barrel.

  • Delta Ring Assembly

This includes the delta ring, weld spring, and snap ring. You only need this when you go with two-piece handguards. 

  • Sights

Only A4 and Flattop AR 15 models allow for adding a "front or rear sight." 

Putting it all Together: AR15 Assembly

After procuring everything you need for your AR 15 project, arrange the tools and begin your AR15 assembly and here's how: 

Assemble Your Forward Assist On the Upper 

The first thing is to assemble the forward assist on the upper, typically consisting of the forward assist, forward assist spring, and roll pin. Turn the upper upside down to let its Picatinny rail flush with the work surface, sliding the spring in either direction, and get the forward assist pin in the bottom to let it stand. Drive a series of "punches" into the upper's side and insert the forward assist assembly, so the pawl is flush with the upper's middle. 

Slide the forward assist assembly into the upper, compress it, and simultaneously do a small drive pin punch until it's flushed. Once it becomes firm, deal a brash punch into it and test out if the forward assist can move freely. 

Install Ejection Port Cover

When installing an ejection port cover assembly, you'll want to hammer a snap ring onto the ejection port cover pin. It's best to start with the end without the snap ring and place the ejection port cover on the upper to ensure it's open, aligning the cover's holes with the upper. Place the ejection port cover pin near the upper's barrel threads. Then, hold the cover spring and grip the longer part of the spring sticking out. 

You'll want to wind the spring until it faces you. Put the long end on the right side, and slide the ejection cover pin until the snap ring stops you. Then, shut the ejection port cover. 

Bolt Carrier Assembly 

Bolt carrier assembly requires a bolt, bolt carrier, firing pin, retaining pin, and bolt cam pin. Start by pressing the bolt into the end of the BGC, then insert the cam pin into the BGC's hole, which is located underneath the bolt carrier key. 

When the cam pin is in place, ensure the holes are aligned with the front and back of the BGC. When aligned, slide the firing pin through the BGC and insert the retaining pin. 

When done well, move on to the charging handle, place a latch spring inside it, and attach a rolling pin at the handle's top. When compressing the charging handle latch, line them up and add the latch roll pin.

Bolt Carrier and Charging Handle 

Install the bolt carrier and charging handle in the upper by inserting the charging handle assembly into the bolt carrier (upside down), then carefully align the tabs on the handles of the grooves of the upper. 

Then, slide the handle assembly to ensure it's inert, pull the bolt out of the carrier until the bolt cam pin can't touch the upper's interior. Now, place the bolt carrier assembly into the charging handle, keeping them aligned. 

Push both into the upper until they click into place. Insert the upper into the action block by removing the assemblies, slipping the action block into the upper's rear, shutting the ejection port cover, and putting the upper into the "block," close, and tighten. 

Inner and Outer Receiver Nut 

Remove the inner barrel retainer nut and outer receiver nut from the handguard by unscrewing them from each other. Then coat the barrel threads using white lithium grease to prevent them from galling. Now, guide the outer receiver nut on the "threads" until it makes contact with the ejection port cover pin. Finally, cover the inner barrel retainer nut with the grease, attach it, and tighten. 

Gas Block 

Insert the gas tube in the three holes where you'll be putting the block. You can do this by unscrewing the bottom of the gas block, sliding it so that it's on the barrel, and threading the tube into it. Tighten the screws back and align the "tube" to the block's hole with the gas hole. After alignment, tighten the entire thing up and insert a rolling pin. 

Adding the Handguards 

Although you can stick with standard parts, installing a free-floating handguard promises a better outcome. To do this, pull the delta ring toward the receiver and ease it out. Simultaneously, remove the flash hider, scope, gas block, and delta ring, requiring you to remove the inner barrel retainer nut. Now, remove the barrel snap ring and return the barrel nut since it'll be the one connecting the free-floating handguard. 

Finally, using a torque wrench, torque the outer receiver nut to confirm if the gas tube is perfectly aligned with the receiver's port. To mount the handguard tightly, use two clamshell braces on the outer receiver nut. You should be able to slide the handguard freely.


AR 15 rifles are some of the most popular guns to date, and you don't always need to go to a gun store to buy one. Not many may know this, but you can make your very own AR 15 from scratch — and it's pretty simple. However, if you don't know anything about its building process or where to begin, this guide can help. Whether you've been assembling rifles and other firearms for years or are starting with the hobby and looking to build your first AR 15, you can do it with ease. 

However, keep in mind that when it comes to building a AR 15 rifle, you must make a few "weighty" decisions — but once you've concluded some items on this guide, you should be able to make your first rifle in no time. Be prepared to invest plenty of time tackling this project since you're likely to experience a couple of setbacks in the process. However, you'll learn from the process and grow. So, enjoy it as much as you can. After all, building a AR 15 is supposed to be fun and fulfilling

We hope this article helped you learn how to create a AR 15 rifle from scratch, making your first experience more accurate, productive, and efficient.

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