Thursday, December 9, 2021

Build your own AR

 From Cheaper Than Dirt:

This is a complete list of everything you need to build an AR-15 rifle. Underneath each component is a suggestion of products the Cheaper Than Dirt! experts use or have used in the past on various builds for DIY ARs.

Of course, our recommendations are not exhaustive. There are so many different ways to configure an AR-15, from mass-produced cheap polymer lowers to mom-and-pop shops machining custom competition, match-grade parts.

Each AR-15 build is going to vary, depending on your reason for building the rifle. Be it a 9mm carbine, destroyer of pigs, long-range precision or simply just a fun firearm, this guide will lead you in the right direction.

The 27 Parts Needed for DIY ARs

Here’s an infographic that quickly shows the parts needed to build an AR. Read more details about each component below (or click here to skip the infographic).

DIY AR Build Components

1. Stripped Lower Receiver

The stripped lower receiver is the serial numbered part of the firearm. Buying the lower receiver works the exact same way as buying a completed firearm. AR-15 stripped lower receivers must ship to an FFL dealer. You will have to pass the federal background check before taking possession of a stripped lower.

2. Lower Parts Kit

To assemble the AR-15 stripped lower, you will need 31 different parts, including the trigger, bolt catch, springs, pivot and takedown down pins, selector switch and hammer. The most convenient way to get all of these parts is by purchasing a full AR-15 lower parts kit.

The kits include all 31 items, including a pistol grip and trigger. However, some items you will probably want to discard from the pre-packaged kit and purchase as separate upgrades.

Here’s an example of installing the pivot pin:

3. Pistol Grip

Located behind the trigger guard and at the back of the rifle is the pistol grip. You grasp this with one hand to aid in shooting the rifle. A basic pistol grip is usually included in the lower parts kit, but many find aftermarket grips fit their hand better.

Here’s a video example of installing the trigger guard:

4. Fire Control Group (Trigger)

The fire control group consists of:

  • Hammer and hammer spring
  • Trigger and trigger spring
  • Disconnector and disconnector spring
  • Two fire control pins

You may use a fully contained trigger unit or individual parts. Fire control group parts are included in the basic lower parts kits. Our experts like to replace the standard trigger group with a match-quality trigger.

Here’s an example of installing the fire control group:

5. Selector

The selector is the safety switch and is included in a basic lower parts kit. Left-handed and ambidextrous selectors are available for DIY ARs.

Here’s an example of installing the selector and pistol grip:

6. Bolt Catch

The bolt catch stops the bolt from traveling forward when the magazine is empty. The standard lower parts kit includes a  basic bolt catch.

Here’s a video example of installing the bolt catch:

7. Magazine Release

The magazine release drops the magazine out of the firearm. The standard lower parts kit includes a magazine release.

8. Bolt Carrier Group

The bolt carrier group holds and moves the bolt. It also resets the hammer. The bolt carrier group includes the bolt carrier, complete bolt, firing pin, carrier pin and gas key.

The gas key feeds gas from the gas tube into the carrier and bolt. The bolt carrier group holds the majority of the gas pressure when the AR-15 is fired. It is what makes the AR-15 function and an essential, if overlooked piece. Read more about the bolt carrier group here.

Here’s a video example of field stripping the bolt carrier group:

9. Buffer

The buffer slows down the bolt on the AR-15, absorbs recoil and reduces wear on the rifle. Buffers come in two different sizes, either rifle or carbine and in four different weights from lightest—the standard—to the heaviest, called an H3 buffer. For an AR-15 chambered in .223 Remington/5.56mm NATO, use the heaviest buffer that allows your rifle to function and consistently lock the rifle’s bolt back.

The type of stock you chose for your AR will determine the size of the buffer you buy. For an A1/A2 fixed stock, purchase a rifle buffer. For a collapsible or adjustable stock, buy a carbine buffer. If you are building your AR in 9mm, you will need to buy a 9mm-specific buffer assembly.

10. Buffer Tube

The buffer tube holds the buffer spring and buffer. Buffer tubes come in three sizes—rifle, MIL-SPEC carbine and commercial carbine. Choose the right size for your DIY ARs’ stock.

Anderson Buffer, buffer tube, and spring
The buffer tube holds the buffer spring and buffer — essential for DIY ARs.

Here’s a video example of installing the buffer tube:

11. Buffer Spring

The buffer spring brings the bolt of the rifle forward, allowing the gun to fire follow-up shots. Rifle stocks—A1 and A2—as well as carbine buffer springs, are different sizes.

12. Barrel

To learn more about AR-15 barrels, read “AR-15 Barrels 101.” There are a number of different barrel lengths, twists and caliber available for DIY ARs.

Ballistic Advantage AR-15 16" barrel

13. Barrel Nut

The barrel nut holds the barrel to the receiver. Typically when you purchase a handguard it will include the barrel nut.

14. Gas Block

The gas block directs gases from the barrel to the gas tube and back into the AR-15’s receiver, allowing it to complete the cycling process so another round will fire.

Yankee Hill Machine low profile gas block

15. Gas Tube

Gases are directed from the gas block to the bolt carrier via the gas tubes. Gas tubes vary in length, coming in rifle, mid-length, carbine and pistol lengths.

16. Upper Receiver

The AR-15 upper receiver holds the forward assist, spring and pin, the ejection port cover, the charging handle, barrel and bolt carrier group. There are many choices when it comes to putting together your upper receiver for DIY ARs.

You can purchase a complete upper receiver assembly that includes the barrel, an upper receiver that has no barrel, but includes the ejection port cover and forward assist, or you can buy a stripped upper receiver that is just the metal housing for all the parts.

17. Upper Receiver Parts Kit

The upper receiver parts kit includes the ejection port door, spring, forward assist parts and sometimes the charging handle. It typically does not include the bolt or carrier.

18. Charging Handle

The charging handle moves the bolt carrier that is inside the upper receiver. Its primary function is to pull the bolt carrier back or to aid in clearing a malfunction.


19. Stock

Luth-AR MBA-3 AR-15 Adjustable carbine stock

AR-15 stocks are either adjustable or fixed. Depending on where you live, an adjustable or collapsible stock is illegal. The AR-15 stock goes on the back of the rifle and allowing you to shoulder it.

20. Handguards

The handguards go around the barrel of the AR-15. It is where you can add accessories and grip your rifle. Handguards are also referred to as the forend, foregrip or forearm. They protect your hands from burning on a hot barrel.

Handguards come in different sizes according to the gas system you choose for your AR-15—rifle, mid-length, carbine and pistol length handguards. When picking out the parts for your rifle, the gas tube will also come in rifle, mid-length, carbine or pistol lengths. Whichever your gas tube is, buy that size handguard.

There are free-float and standard handguards. Standard handguards will touch the rifle’s barrel, while free-floating handguards will not. Free-floating handguards are more difficult to install than standard, but you will get slightly better accuracy at longer distances using free-float handguards.

They also are either smooth or have rails on them. Handguards serve a valid function, however, and many people buy them purely on their aesthetic value.

aero precision atlas s-one free float handguard

21. Delta Ring Assembly

The delta ring assembly includes the delta ring, weld spring and snap ring. If you choose free-float handguards, you will not need a delta ring assembly.

Spikes Tactical Delta Ring

22. Sights

AR-15 upper receivers come in two different types, either an A2 or A3 (flat top). Its fixed carry handle with integrated iron sights characterizes the A2 upper receiver.

The A3 flat top upper has no carry handle, but does have a Picatinny rail installed. The A3 flat top upper allows you to add sights and optics, while the A2 (carry handle upper) does not.

23. Handguard Cap

The handguard cap secures the front of standard handguards. It is not needed on free-float handguards.

LBE Unlimited standard handguard cap

24. Muzzle Device

Aero Precision AR-15 VG6 Epsilon Muzzle Device

There are two types of muzzle devices. You may put either a muzzle brake—sometimes called a compensator—or flash suppressor/flash hider on your rifle.

The muzzle brake helps reduce recoil and muzzle rise while the flash hider suppresses the visible flash from the barrel when the rifle is fired. Some states restrict flash suppressors for DIY ARs, but may allow muzzle brakes. Check your local laws before ordering.

25. Magazines

UTG AR-15 .223/5.56 Polymer window magazine 30 rounds

AR-15 magazine capacity ranges from five to 100 rounds. Some states restrict magazine capacity. Check your state laws before ordering.

26. Optics

Optics for the AR-15 include traditional riflescopes with magnification or electronic red dot and non-electronic illuminated sights that offer no magnification.

EOTech 512.A65 Holographic Red Dot Sight

27. Extras

“Extras” include things such as sling mounts and attachments, vertical grips and tools.

For instructions on how to install these parts, watch these videos from “Building Your AR Lower Receiver.”


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