Custom Built vs Fully Assembled AR-15

Due to it’s modular nature, the AR-15 is one of the most flexible weapons out there. You can configure it for a specific purpose such as competition shooting, plinking, hunting and, of course, self-defense. In fact, if you’re looking to custom build your very first rifle, starting with an AR-15 is a good choice.

So, should you build a custom rifle, or buy a preconfigured model? Even for experienced shooters this is a tough question.

Building your own AR-15 gives you the chance to get every part exactly how you want it, but it often ends up being more expensive.  And with so many builds on the market, there’s typically something for everyone.

Build or Buy?

Let’s look at both the pros and cons of building and buying so you can make the decision for yourself after analyzing them.

Buying a Fully Assembled AR-15

To be honest, buying seems like the easier and more convenient option. If you’re a gun rookie or a beginner, I suggest that you buy a factory-made AR-15 rather than trying to build it yourself. With the product in front of your eyes, you are able to do research to find more about the different components and parts of the AR-15. So, the advantages of buying are:

  • Convenient and hassle free
  • Perfect fit and compatibility
  • Good accuracy
  • User peace of mind

The disadvantages on the other hand are:

  • Lesser creativity
  • Lack of comfort
  • Plain in nature and design
  • Slightly more expensive

To summarize, a lot of people buy the AR-15 because you don’t have to go through the hassle of building them yourself because building them is not an easy task, to be honest. You need to know what you’re doing and equipped with the right technical skills and tools to machine the firearm with great precision. Hence why, buying the weapon provides peace of mind to many people, especially beginners or not-so handy people.

When you buy the AR-15, the fit and compatibility will most likely be accurate and perfect because you get the whole package with you.  However, you can only expect a working, but simple firearm. In other words, buying the weapon off the shelf will give you a fully-functioning weapon no doubt, but without your own touch and creativity. However, you can always remedy that by upgrading certain parts to your preferred component brand.

Last but not least, buying the firearm would cost you slightly more than building it. This is because you may not like some of the factory-assembled firearm parts, hence to change them, you need to fork out extra cash for an upgrade.

Building Your Own AR-15

Professionals as well as experienced shooters usually opt to build their own AR-15 rifle, according to their own comfort, preference and creativity due to the firearm’s highly modular nature. Let’s take a look at the pros and cons of building your very own AR rifle. Some of the pros are:

  • Better familiarity with rifle
  • Good experience
  • Apply your own custom design
  • More comfort

Conversely, the cons include:

  • Tools/technical skills required
  • Need good knowledge on AR-15
  • Hands-on experience
  • Time invested

To summarize, building your own AR-15 will leave you with a proud and satisfactory feeling in your chest, especially if it works fine with good precision. Experienced shooters love building their own firearm because they get to customize the weapon just the way they want, with their favorite brands for each component. On top of that, the experience of building a firearm is priceless and this experience in return will assist you to work with other rifles.

Apart from that, getting each component (custom AR-15 parts) with high quality and good reviews will result in a high performance rifle overall. You also get to know you rifle well, especially on how it works inside and outside. Believe me, the experience of getting to know your rifle by building them is way better from reading the user manual booklet.

Moving on to the cons, you need a vast amount of knowledge dealing with guns not to mention, invest a fair amount of time to build it, especially if you’re not used to building firearms. In terms of technical skills, diligence and determination with the right gunsmithing tools are the key to build a high-performance AR-15. Some experience would help ease the process and cut the time spent but that doesn’t mean that it’s impossible to build the AR-15, especially if you’re inexperienced.

Before we look at how you should go about building your custom AR-15, you will need to have these necessary parts listed below.

Parts of AR-15 Firearm

Before knowing how to custom build your own AR-15, you should be aware of its parts. These parts include the lower receiver and their parts kit, upper receiver and their parts kit, buffer tube (also known as lower receiver extension), buffer spring, charging handle, buffer, bolt carrier group, trigger, handguards, buttstock, magazine, as well as barrel and gas block system. If you’re a beginner, this review would do you good because I’ll be briefly explaining on each part.

1. Lower receivers

We’ll start with the lower receiver first. The lower receiver carries the serial number, hence you need a Federal Firearms License (FFL) to purchase them. That being said, the lower basically houses the firing mechanism which consists of the trigger, trigger group and magazine. In terms of construction, they are made in 3 different styles which are the billet, forged and 80% assembled.

For the billet style, the lower is machined from a single block of metal and they tend to have a more aesthetic appearance and characteristic, so you can make unique changes to them according to your preference. They’re not as strong as the forged receivers however. More so, the billet style lower costs more than the forged and 80% assembled because it requires the most time and workmanship.

The forged style on the other hand includes the metal being CNC machined and heat treated to the shape of the lower receiver. As a result of that, the metal is compressed well therefore, making it extra strong and durable. In fact, the forged lower results in the strongest quality product among the three different construction styles. In addition to that, the 80% assembled refers to the receiver not fully assembled, therefore not considered a firearm.

Thus, you don’t require a FFL license to buy the 80% assembled lower. The 80% assembled may be cheap, however you need make extra modifications and add additional AR-15 parts with your own tools to complete the lower receiver assembly. Some of these additional work include adding threads for buffer tube, bolt release cavity as well as rear pivot pin hole in the pre-machined areas. If you’re a handy and technical person, you should by all means go for this type of lower because you can customize it according to your preference.

2. AR-15 Upper Receivers

Moving on to the upper receiver, it is equipped with a highly modular design so you are able to customize the handle, barrel, rail system and bolt design, with added convenience. You can do so with both the upper and lower by getting the upper and lower parts kit respectively. Hence, it can be said that the upper part houses the bolt and barrel of the rifle. Similar to the lower, the upper also comes with either the forged or billet receiver style.

3. Magazines

The magazine (whether the removable or fixed mag) on the other hand is the ammo storage or feeding device in a firearm. The number of rounds a magazine can accommodate varies from as high as 60 to as low as 10 or 20 rounds, though the common round utilized are 30 rounds. For your information, the magazine mainly consists of a spring, spring follower (anti-tilt) and a feed lip.

Furthermore, the follower usually comes with an anti-tilt feature to prevent jamming of the cartridges in the midst of feeding. It functions to hold the ammunition in place to ensure that they load into the breach of the barrel properly. The spring puts good pressure on the cartridges so they rise with enough power and force to hit the feed lip meanwhile the feed lip, located at the top of the mag, keeps the ammo in the magazine until it is pushed forward and into the breach with the bolt.

4. Trigger

The trigger can be said as the key interface between the firearm and the user. Hence, it is essential to get a smooth working trigger that is equipped with the right pull weight, together with a clean break. If you’re planning to custom build your AR-15, you should go for the AR-15 trigger rather than the factory stock trigger so you can make customizations which in my case, improved my control and confidence when using them. Also, get yourself an AR-15 scope to improve the accuracy of your shot!

By customizations, I mean that you’re able to modify the trigger placement on the lower by drilling, cutting and gunsmithing them to ensure perfect fit and proper alignment. Based on my experience, I prefer drop-in triggers because they are easy and convenient to assemble. In other words, you just have to drop the trigger into the lower receiver, secure them with trigger pins and voila, you’re good to go. However, if the fit is not perfect, then you are required to do some gunsmithing work.

5. Gas Block System

What is a gas block system? A gas block refers to a device that fits over the tiny opening (gas port) on the AR-15 barrel. When the rifle is fired, the projectile travels along the barrel with high velocity past this hole, where some hot burning gasses escape through it. The burning gas then enters the gas block and is directed down the gas tube.

There are two types of gas block which are the standard and adjustable ones. The standard gas block allows a constant and fixed amount of gas to travel in the gas tube while the latter gives you the opportunity to adjust the amount of gas going in the tube. You’ll need the adjustable gas block mostly for a suppressed use to tame the burning gas. Also, it can be used for over-gassed systems, rifle with light carriers and buffers as well as buffer springs with reduced power.

Before proceeding, let’s take a further look on a pistol gas system. So, on your AR-15, there is a gas port (tiny opening) on the barrel that lets out some of the hot gases when the shot is fired. This gas flows via gas block and gas tube into the receiver. When it is in the receiver, the bolt carrier group is powered up and automatically cycles the next round, whereby this whole process is known as the direct impingement gas system.

For your information, the length of the gas system is measured from the receiver to the gas port. It increases with the barrel length due to the ‘dwell time’. The term ‘dwell time’ refers to the how long the projectile will be in the barrel after the shot is fired. Logically speaking, the dwell time is longer with a longer barrel since the bullet has to travel the extra distance.

It is important to know the correct gas system length for your barrel because too much barrel length will result in too much gas flow into the receiver hence leading to extra recoil and wear on your firearm. Conversely, too little barrel length may cause your rifle to jam since there isn’t enough gas flowing into the receiver. You can check out the respective gas system length for each type of weapon in the table below.

System TypeLength of BarrelPort Distance
Rifle>20 inches12 inches
Mid14-20 inches9 inches
Carbine10-18 inches7 inches
Pistol<10 inches4 inches

6. Bolt Carrier Group & Bolt

How does an AR-15 bolt carrier group (BCG) work inside a direct impingement gas system? Before that, you should know that a bolt carrier group is one of the key components in the AR-15, therefore if you’re going to spend any extra bucks on your rifle, you should at least start with getting a really good quality bolt carrier group. For your information, one of the critical elements of your bolt carrier group as far as the gas system goes, is the gas key, which functions to connect with the gas tube.

Once a round has been fired through the barrel, the burning gases produced comes through the gas tube and hits the gas key. The gasses are then forced down into the bolt carrier group and the bolt itself. In the bolt carrier group, there are ports (holes) where the gasses escape and fill up in the upper receiver. The bolt on the other hand is attached to the end of the bolt carrier group.

It’s locked up into your chamber but once the gas expands inside the bolt, it actually pushes the bolt into a rear position which in return unlocks the bolt. The bolt actually rotates, so when it is going into the chamber, it enters in through the teeth, goes past the teeth and then closes down. When it closes down, the bolt turns and locks into the chamber.

7. Barrel

In addition to that, a barrel is said to have corresponding entrance points for the teeth on the bolt, so they accommodate each other well. For your information, the barrel is the straight shooting tube on your firearm, which transports high pressure gases (when the rifle is fired) behind the projectile, to propel it out of the muzzle with high speed.

In fact, gun barrels are usually rifled, in which they consist of grooves cut in a spiral nature down the length of the barrel. Rifling is done to produce a spin on the cartridges that pass through it therefore producing an accurate shot, because they are able to spin easily in their flight with their oblong shape. Moreover, the gas port is located in the barrel.

As the gas passes through the barrel and the projectile moves forward, they are forced up through the port and typically there is a gas block that functions to direct the gas into the gas tube. Not only that, you should know that debris and carbon build-up all over the bolt, therefore it needs frequent cleaning, you can do so with an AR-15 cleaning kit.

8. Charging Handle

Apart from that, the AR-15 rifle is also equipped with a charging handle, which when operated, results in the hammer being moved to the ‘ready to fire’ function. That being said, the charging handle has a small opening at the end that corresponds with the gas key. When firing the weapon, the bolt actually moves into the charging handle. That way, the charging handle refrains from getting pulled back and hitting you in the face.

Conversely, if you want to charge your weapon, all you have to do is grab hold of the charging handle and pull it backwards, which in return pulls the bolt back as well. In other words, it allows the operator to pull the bolt back to the rear. More so, the charging handle also assists in the ejection of unfired bullets from the chamber as well as clears stoppages such as the ammo getting jammed. Hence, it acts as a forward assist where it moves the bolt in to the battery.

9. Buffer & Buffer Spring

A buffer or also known as recoil buffer is an aftermarket firearm component. It kills two bird with one stone because it functions to reduce the velocity as well as cushion the impact of the rifle therefore, reducing the recoil produced. So, how does it work?

Each time the projectile is fired, the bolt carrier group follows through the action in order to load the projectile into the chamber. When the bolt carrier is pushed back however, it hits the buffer as well as buffer spring inside the buffer tube which in return pushes the bolt carrier forward again to pick up a round.

In addition to that, the buffer spring acts as an additional weight which assists the carrier and bolt to move back in the right position after the shot is fired. When purchasing a buffer, you should get the right buffer weight which comes in handy to reduce your AR-15’s recoil. Here are three tips to ensure that your buffer spring is working properly.

  • Examine your buffer and spring close-up
  • Measure your buffer springs
  • Analyze the spring coils

10. Handguard

First things first, a handguard is attached on the front of your firearm, wrapped around the barrel, in order to grip the firearm from the front. The handguard comes in handy to guarantee your protection from accidentally touching the hot barrel. For your information, the barrel gets hot when the shot is fired due to the hot burning gases that travels in it together with the projectile.

There are two types of handguards which consist of the drop-in and free-floating type. The free-floating handguard is designed in such a way that they don’t make contact with the barrel of your firearm. In fact, they attach directly to the barrel nut which is secured to the upper receiver therefore allowing the handguard to ‘float’ above the barrel. The free-float design keeps your shots as accurate as possible because there is a slimmer chance of your barrel’s position to be altered if the handguard doesn’t touch the barrel.

The drop-in style on the other hand is well-known for its simplicity. That being said, you don’t need to make any modifications on your rifle with a drop-in handguard, for your added convenience. Most drop-in handguards come in two pieces (which are screwed together finally) to prevent the need to remove the barrel. Hence, if your rifle comes with a delta ring and front sight base (FSB), it is best to get a drop-in handguard, to ensure the best performance.

Also, don’t forget to get yourself an AR-15 bipod.

11. Buttstock

A buttstock or commonly known as stock by itself attaches to the barreled action and firing mechanism of your rifle. The stock is rather easy to identify because they are commonly held against your shoulder when you’re about to take a shot. In other words, it provides the shooter firm support, therefore resulting in better aim and stability. Not only that, the stock also absorbs the recoil into the shooter’s body.

In addition to that, the gun stock is divided into two parks consisting of the butt (rear part) and fore-end (front part). The butt corresponds with the shooter’s trigger hand and braced by the shooter’s shoulder for improved stability meanwhile the fore-end supports the receiver and absorbs the recoil from the barrel.

How to Custom Build the AR-15

In my opinion, it is important to make your gun reflect who you are and have a personality like you do since you’re going to frequently use them. By building a custom AR-15 rifle, it helps you understand and familiarize yourself with the weapon well. Before building your AR-15 firearm, you should bear in mind these following precautions:

1)Safety comes first

You can should wear safety glasses and gloves at all times, for ultimate user protection. An apron will also come in handy to protect your clothing when dealing with machines or grease and lubricants.

2)Tidy and clean floor area

Your floor area at your workspace should be clean and tidy at all times. Since you’ll be handling small pins and springs, they will most likely fall on the ground at one point so with a clean floor, you can easily find that missing part with added convenience. The tidy floor area also do not restrict your movement, hence you can move around your workspace easily.

3)Getting the right tools

Building a whole AR-15 rifle is no easy task, hence you’ll need a lot of gunsmithing tools and certain machines to make a high-performance rifle, with maximum precision. Using the right tools are important to maintain the precision of your weapon, such as good alignment between your upper and lower receiver. Not only that, try utilizing tools that will not mar the finish of your weapon.

4)Clean and organized workbench area

Believe me when I say this, a clean workspace do lighten up your mood and spirits. In other words, the incredible power of an organized workspace will do wonders in helping you build your AR-15 with added convenience and peace of mind. In fact, you can find the tools and components you want with maximum ease if they’re organized in the first place.


Prior to building your AR-15 rifle, you should first ask yourself the primary purpose of the firearm, whether it’s used for self-defense, plinking, hunting or range shooting so you can choose the right AR-15 custom component and accessories. After that, get ready with your equipment and tools. In other words, you can prepare by arrange all your tools and AR-15 custom parts on the workbench for easy access later on.

On top of that, you can even group the custom parts together such as the buffer tube, buffer and buffer spring for instance, for convenient access in the future. The steps to building an AR-15 are as follows:

1. Install Forward Assist

Coming to the building process, you can firstly install the forward assist on the AR-15 upper receiver. For your information, the forward assist assembly consists of the roll pin, spring and the forward assist itself.  To begin, you’re to slide the spring on the forward assist, without taking the direction into consideration.  Then, attach the forward assist pin into the upper receiver via the roll pin starter punch followed by inserting the forward assist assembly into the upper.

Then, drive the roll pin in to attach both the forward assist assembly and upper receiver. Once the pin is inside, you need not have to hold the forward assist in place. Instead, you can utilize a brass punch which comes in handy to drive the pin in with better force. Last but not least, test the forward assist whether it is able to move freely in and out, when compressed. If it does, your forward assist has been successfully installed.

2. Move on to the ejection port cover

Next on the list is the ejection port cover. You’re to carefully set the ejection port cover pin snap ring onto the end of the cover pin. Once doing so, you should hammer them all the way to attach them together. When hammering, bear in mind to make a direct and downward strike on the snap ring so it doesn’t fly off your workbench. Next, you’re to place the port cover on the upper receiver in the open position, keep in mind to make sure that the holes in the port cover are accurately lined up with the holes in the upper.

The ejection port cover spring goes into the middle opening of the port cover. With the spring held under tension, you’re to slide the ejection port cover pin all the way through until the pin snap ring stops your progress. Then, close the port cover, making sure it snaps shut. To test it out, reach inside the upper and push out the port cover, making sure it opens up. If it does, you’re good to go.

3. Assemble bolt & bolt carrier group

The bolt is pushed all the way to the end of the bolt carrier in which you need to make sure that the hole through the middle of the bolt is well-aligned with the bolt carrier gas key. In addition to that, further insert the bolt cam pin via the large opening in the bolt carrier group. Tip: Keep the bolt cam pin holes perpendicular to bolt carrier key so the key is properly cleared for easy insertion.

Once the bolt cam pin has been successfully lined up at the front and back of the bolt carrier, the firing pin is able to slide through. In fact, you’re to slide the firing pin through the bolt carrier group, towards the bolt, until it cannot go any further. Lastly, slide the firing retaining pin through the bolt carrier.

Due to the bolt carrier being hollow in shape, retaining pin should have proper alignment with the hollow part of the bolt carrier so it can slide in with maximum ease. Before moving on to the charging handle, test whether the bolt is able to move in and out of the bolt carrier group freely.

4. Install charging handle

Start by sliding the charging handle latch spring into the charging handle itself. Then, insert the latch roll pin into the top of the charging handle so it is able to stand on its own, you can utilize a roll pin starter punch to assist you in this process. The last piece of the puzzle is nothing but lining up the holes followed by driving the roll pin until it is intact and flush, while compressing the latch into the charging handle.

Then, you just have to install the bolt carrier as well as charging handle assembly into the upper receiver. In fact, you’re to push them into the upper receiver until they firmly click into place. While doing so, the ejection port assembly should snap open. After that, fix the upper receiver into the action block and further tighten it in the vise.

5. Attach on the barrel

Moving on to the barrel, you’re to insert the barrel into the threaded end of your AR-15 upper receiver. Care to ensure that the pin on the barrel is well-aligned with the slots in the upper receiver for a perfect fit. Then, the barrel is slid all the way into the upper until the pin knocks into the back of the slot.

Once you’re done with inserting the barrel, you can proceed to fix the outer receiver nut as well as inner barrel retainer nut on the barrel threads, however make sure that the gas holes are aligned well. You know you’re doing it right if the gas tube slides freely through the gas holes after installation.

6. Fix gas tube and gas block

Apart from that, this assembly consists of the gas tube roll pin, gas block and gas tube altogether. Firstly, you’re to insert the gas tube into gas holes that are located on the outer receiver nut, barrel receiver nut as well as upper receiver. Then, loosen the set screws at the bottom of the gas block in order for it to slide over the barrel, followed by sliding the gas block all the way into to barrel.

That being said, you’re to slide it to its maximum point, which in return guides the gas tube into the hole in the gas block. Tighten the set screws on the gas block so it stays secured but before that, make sure to orient the gas block so that the gas tube and gas hole are well-aligned. Finally, you’re to drive the roll pin through the gas tube and block.

7. Attach handguard

You can either choose the drop-in or free-float handguard. I’m going to go with the free-floating handguard here. Firstly, you need to install the plug screws and sling swivel studs on top of the free float handguard. To accomplish this process, you’re to detach the sling swivel stud from the retainer nut and place the retainer nut into the handguard track. Then, screw the stud into the retainer nut.

Proper alignment is of utmost importance so you should accurately line up the screw holes of the free float handguard with the outer receiver nut. Once doing so, secure it by flat head screws. Now, your AR-15 upper receiver assembly is good to go, to be attached to the lower.


In a nutshell, this review basically explains the differences between custom building an AR-15 and buying it. If you’re planning to custom build it, I hope that the steps above will guide you. No matter which method of getting yourself an AR-15, happy shooting!

If you’re looking for a case to store and transport safely your AR-15, get either a great soft or hard case, designed specially for Armalite rifles.