How To Build Your Own AR 15: Parts Guide

So, you want to build your own AR 15? Great! The modularity and customization are what makes the venerable, all-too-popular black rifle so awesome.

This little .223 or 5.56 -slingin’ gun is widely considered the adult Lego toy of the gun world.

However, as we know, guns are NOT toys.

If you are interested in piecing together your own AR-15, you have already realized the value of doing so.

You will get to customize your rifle to your exact needs. You will get to spend as much or as little as you would like to get the features (or lack thereof) that you desire.

Building your own is the best way to get down and dirty with the design of the AR, and to know it inside out. It will require you to gain knowledge, skill, and proficiency with the weapon.​

In this article, we are going to take you through all of the parts that go into an AR in great detail. We will also give you suggestions on the top parts to get.​

Disclosure:   Some of the links in this article are affiliate links, where I make a small commission at no extra cost to you.

Build or Buy?

Before we get into the details, it's important to stop and address the question on a lot of people's minds. Should you build your own or buy a manufacture's rifle?

The AR has a rich history and is a great weapon platform. It is one of the most iconic guns representing the 2nd Amendment, and is often seen with Molon Labe.

There are many factors at play here, and you are going to be the only one that can truly answer the question for yourself.

Keep in mind that AR-15's are a bit complicated. If you decide to build your own, you will need to do a lot of research and possibly consult with some experts through the process.

It is possible to do it wrong and mess things up. You also have to be fully aware of your federal, state, and local laws to make sure you are compliant.​

If you are willing to do all of the work involved, and you enjoy the process, then it probably makes a lot of sense for you to build your own. If not, there are some really awesome AR-15s you can get off the shelf.

Another big debate is getting an AR-10 vs AR-15.​ If you are curious, we put together a list of the best AR-10's.

Custom Build Breakdown

When it comes to projects, everyone likes lists. Before we break down how to build your own AR 15, let's make a list.

The parts you will need:

  1. ​Barrel
  2. Muzzle Device
  3. Handguard
  4. Upper Receiver
  5. Gas Block and Tube
  6. Bolt Carrier Group and Charging Handle
  7. Lower Receiver
  8. Trigger
  9. Lower Parts Kit
  10. Buffer, Tube and Spring
  11. Stock

To simplify things, you can pick up a full-built upper that includes a barrel, gas block and tube, muzzle device, upper receiver, and usually the bolt carrier group and charging handle preassembled.

You can do the same with your lower. Simply pick up a full-built lower and slap it onto an upper. Now you are ready to rock.

There are thousands of combinations of parts on uppers and lowers. We are going to break down everything piece by piece.

We will even make recommendations for each part! Let's get started:

1. Barrel

The barrel is arguably the most important piece of your AR build. There is a lot to consider. We will keep it simple by explaining each barrel type and attribute needed. If you want a barrel deep dive, check out our article on the top AR-15 barrels.

Stainless Barrel

These bad boys tend to provide the most accuracy. They are often found on bench rifles and competition shooters.

We personally recommend the Krieger Match-Grade Custom Cut-Rifle Varmatch Barrel. This is perhaps the most accurate production AR barrel available. It costs around $370. You cannot beat the quality or shot groups it produces.

Hammer Forged Barrel

Cold hammer forging (CHF) produces a barrel that is tougher than standard pressed barrels. The hardened, compressed rifling produces better accuracy than run-of-the-mill cut or button rifling. CHF barrels are usually made from mil-spec Chromoly steel.

This offers the same level of ruggedness the military puts into its service rifles. If you are building an M4 clone or USGI-like rifle, we recommend BCM’s Standard 16” M4 Barrel. It costs around $250 and provides something tough and proven.

Standard Chromoly Barrel

A standard Chromoly barrel is the every man's barrel in the black rifle world. It produces accuracy out to at least 300 yards. It uses traditional rifling that will last a few thousand rounds without getting sloppy.

Standard Chromoly barrels can be chrome-lined, but many are not to save cost. Chrome lining just adds some barrel life. Chances are you will stop shooting your rifle before you wear through your rifling that much.

If you are building a good, budget AR, we recommend the DPMS’s 16” Lightweight Chromoly Barrel for its low cost of about $150 and users’ reviews about its modest accuracy and reliability.

Barrel Profiles

You can choose between a heavy barrel, a traditional “government” or M4 profile, or a lightweight profile. The profile is simply how much “beef” the barrel boasts.

A lighter barrel may not be as accurate, but it saves weight. The M4 profile is the middle-of-the-road choice. Heavy or bull barrels provide the most accuracy.

Barrel Length

AR-15 rifle barrels can be as short as 14.6 inches with a pinned muzzle device that is at least 2 inches. Anything less is considered a pistol.

The barrels go all the way up to 24 inches and beyond. Longer barrels produce more accuracy and are often found on bench rifles or hunting rifles.

Shorter barrels are more maneuverable and are found on common ARs and competition rifles. The standard size for most ARs is 16 inches, but 18-inch barrels are popular as well.

Gas System

AR barrels come with carbine-length, mid-length, and rifle-length gas systems. Shorter gas systems mean smaller handguards, less weight, and less room for accessories.

The standard for the AR-15 is a mid-length system; however, carbine-length systems are popular on USGI replica rifles. Bench and accuracy rifles work best with rifle-length systems.

2. Muzzle Device

Chances are your black rifle’s barrel will come threaded for a muzzle device. About 98% of all AR-15s use one. You can select from three choices:

Compensator

Compensators reduce muzzle rise and improves accuracy. Check out our article on the top AR-15 compensators.

We recommend the Effin’ A MKII Compensator for its performance, reducing barrel rise to practically zero. It is fully adjustable and runs just about $100.

Flash suppressor

Flash suppressors reduce muzzle blast and may reduce muzzle rise.

We recommend keeping it simple and sticking with the venerable A2 Birdcage Flash Suppressor. It is good enough for the military’s branches. It can be found for around $30.

Muzzle brake

Muzzle brakes reduce felt recoil and may also reduce barrel rise. Check out our article on the top AR-15 muzzle brakes.

We recommend the SJC Titan Compensator. It reduces felt recoil by up to 80%, which is a remarkable figure. It can be had for around $90. This is not too shabby considering the comfort and accuracy it fosters.

3. Handguard

The handguard on your AR will provide comfort, convenience, and a place to hang accessories and front sights. Handguards are generally split into two categories: free-floating and two-piece.

Free-floating handguards actually do not touch the barrel thus increasing accuracy. Two-piece handguards connect to the barrel around the gas block. Two-piece handguards tend to be tighter and lighter in weight.

You can choose from a smooth handguard that functions solely as a place to put your hand. Alternatively, you can choose from traditional Picatinny rail-equipped handguards or M-Lok or Keymod handguards.

Each type is simply an attachment method for accessories and sights. The Picatinny method of attachment is the most common and popular.

4. The Upper Receiver

Upper receivers are pretty simple pieces of aluminum. You can go with any reputable brand and you will walk away with a decent upper with a nice finish.

The only factors you should consider are whether the upper receiver includes a dust cover and forward assist. Neither one is really needed unless you are rolling around in the mud with your rifle on a daily basis.

Anderson Manufacturing’s Standard AR-15 Stripped Upper Receiver offers a quality mil-spec finish and can be had for $50.

5. Gas Block and Tube

These two little devices work in tandem to cycle your rifle. While the gas tube is essentially universal for most upper receivers, the gas block can vary slightly.

You can opt for a traditional A2 front sight post, M4/military style, which incorporates the gas block into the sight post itself.

You can elect for any gas block that will clear your hand guard without interfering with attachments or front sights.

Some gas blocks can be tucked under the handguard. They can be exposed and provide additional attachment points with integrated rails.

We recommend the AR-Stoner Gas block, a Low Profile option that costs $20 with a standard phosphate finish. If you want the traditional A2 block, check out Palmetto State Armory’s Gas Block w/ Bayonet Lug for $26.

ar-15

6. Bolt Carrier Group and Charging Handle

The bolt carrier group, or BCG, is what cycles and ejects cartridges in your AR. Again, the USGI-type M16 bolt carrier group is a classic favorite. A decent one should run you around $100.

You can opt for a nickel-plated or nickel boron BCG, which simply uses a different finish than the standard phosphate coatings on most BCGs. These nickel finishes provide smoother cycling and better wear.

However, they can cost up to twice as much as a traditional bolt carrier group. Based on price and popularity, we recommend Palmetto State Armory’s Full Auto Bolt Carrier Group. At $90 and with great ratings, it is an easy great buy.

The charging handle is also pretty standard stuff, but you can elect to pick one up that provides extended finger grips or ambidextrous release levers.

A standard phosphate-coated charging handle should run you around $30. However, fancy handles with those ergonomic treatments can run up to $100 or more.

Palmetto State Armory’s Forged Mil-Spec Charging Handle is a cool $25 and is highly rated.

If you want total ergonomics, we highly recommend the Geissele Airborne Charging Handle. This handle with extended finger grips and smooth operation can be yours for around $100.

7. Lower Receiver

The lower receiver acts as the tub in which your lower parts kit will live. The lower parts kit is the most important factor of any lower receiver because it controls your weapon’s cycling functions including your trigger.

For a complete run-down, check out our article on the top AR-15 lower receivers.​

A good, entry-level stripped lower receiver should cost you around $60. We recommend PSA’s Blemished Safe/Fire Lower at that price for great possible value.

If you want to go full-tilt with a premium lower, check out Seekins Precision SBA15 Stripped Lower.

This aesthetically pleasing lower includes some innovative features like an ambidextrous bolt release, enhanced bolt catch and a quick-access mag release for around $250.

8. Trigger

The trigger is one of the most important features that you will put in your AR. It acts as the connecting point between you, the shooter, and the function of the entire weapon system. For a full rundown, check out our article on the top AR-15 triggers.

A good trigger will provide few negative factors. It will reduce or eliminate take-up (extra slop), overtravel (the trigger moving too far inward after firing), and creep (that pull of the lever before anything actually goes boom).

Some triggers act as simple drop-in units that make for an easy installation and removal. Others are conventional kits that must be installed piece-by-piece and spring-by-spring.

The lower parts kits provided by most reputable dealers include acceptable trigger assemblies. They are USGI-like in their performance.

If you want something a little better, look at the JP Competition Trigger. This single-stage trigger is crisp with a 3 to 3.5-pound trigger pull and runs around $115.

If you want to go full bore and get top of the line, take a look at the American Trigger AR Gold unit. It is quite literally the most amazing trigger we have ever seen.

This trigger provides the finest fabrication tolerances and absolutely no take-up, overtravel or creep. It also has the shortest reset available and an adjustable 3.5-pound trigger pull. It can be yours for $280.

9. Lower Parts Kit

Whether you decide to grab an upgraded trigger or not, you will still need a lower parts kit to outfit your stripped lower receiver.

The lower parts kit includes all those tiny little pieces that make your weapon cycle and function properly, including the bolt catch and release, magazine release, dust cover, pistol grip, and certain trigger components not included with upgraded trigger kits.

The Anderson Lower Parts Kit is a highly rated favorite, featuring a conventional M4 pistol grip and USGI single-stage trigger for around $60.

Lower parts kit pieces are generally universal. There is little to discern between the different brands—save for the trigger.

10. Buffer, Tube, and Spring

Your black rifle’s buffer, tube, and spring function as the recoil component of the weapon system. The buffer and spring help the bolt carrier group retract and travel back to the receiver, thus cycling the rifle.

AR buffers have different weights that determine how hard or soft your weapon cycles. Shorter gas systems like a carbine-length gas system require a heavier buffer to mitigate all that force. A long, rifle-length gas system requires a lighter buffer.

Generally, most AR systems work well with an H1, H2, or H3 buffer. We recommend the H2, the standard for most rifles. Bravo Company USA’s H2 Carbine Buffer is a perfectly weighted favorite and can be had for around $30.

Just keep in mind that lower receivers and buffer tubes come in two sizes: Mil-spec and commercial.

One is not better than the other one, but the buffer tube and receiver’s tube diameters are different. Their diameters are 1.148” for mil-spec and 1.168” for commercial.

11. Stock

The stock is the last primary, critical piece you will need to build your AR-15. You will have to decide what type of application you will be using your rifle for and what kind of rifle you are building before you choose a stock.

For a deep dive, check out our article on the top AR-15 stocks.​

The everyman’s AR-15 with a standard 16-inch barrel, carbine-length gas system, and conventional two-piece handguard will do just fine with a collapsible M4-style stock.

If that sounds like you, we recommend the Magpul MOE. It is one of the most popular AR stocks on the market and features a skeletonized, lightweight design with a comfortable cheek weld. This sells for around $40.

If you want to run something with convenient storage features and even more comfort, check out Magpul’s ACS carbine stock with flared cheek welds and battery compartments.

This is a favorite among service members. It features multiple adjustment points for the best sight picture.

Finally, if you are building a bench rifle or hunting AR, look at the MBA-1 Rifle Stock.

This fixed stock uses a standard A1 or A2 buffer tube and provides an adjustable cheek riser with 1 inch of height adjustment for the perfect sight picture while standing or resting. An optional butt pad provides even more comfort.

The whole system can be had for $140. This is a lot less expensive than other fixed AR stocks on the market.

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