Firearms

DIY ARs — Building Your Own AR-15

Picture shows a black, stripped lower receiver (the firing part) of an AR-15.

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 toy, this guide will lead you in the right direction.

The 27 Parts Needed for DIY ARs

 

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.

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.

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.

  • CMC drop-in single stage trigger
  • CMMG two-stage trigger

    Trigger assembly for an AR-15 rifle
    The CMC triggers come in single-stage or two-stage, set at 2-3.5 pounds. It’s a crucial component for DIY ARs.

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.

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.

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.

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.

  • Technical Grinding and Machining aluminum buffer tube
  • Primary Weapons Systems enhanced MIL-SPEC buffer tube
  • Leapers UTG MIL-SPEC buffer tube
  • DPMS 6 position carbine MIL-SPEC buffer tube
Buffer spring and buffer tube for an AR-15 rifle
The buffer tube holds the buffer spring and buffer — essential for DIY ARs.

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.

  • TAPCO buffer spring
  • Guntec buffer spring

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.

  • M4 barrels

13. Barrel nut

The barrel nut holds the barrel to the receiver.

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.

  • VLTOR Weapons Systems low profile gas block
  • Yankee Hill Machine low profile gas block
  • Bravo Company gas block

15. 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.

  • Texas Black Rifle Company fully assembled upper receiver
  • Anderson Manufacturing stripped A3 upper with M4 feed ramps
  • CMMG Mk4 upper assembly
  • Vltor Weapon Systems MIL-SPEC upper with forward assist
  • Rock River Arms complete upper assemblies

16. 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.

17. 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.

18. Gas tube

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

19. Stock

Adjustable black AR-15 buttstock DIY ARs
AR-15 stocks — a must for DIY ARs — are either A2 fixed or collapsible.

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.

  • Magpul MOE carbine stock
  • Mako survival buttstock
  • Safariland Super-Stoc collapsible stock
  • Mission First Tactical Battlelink Minimalist MIL-SPEC stock

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.

  • Daniel Defense free float handguard
  • Troy Industries Alpha handguard
  • Magpul MOE drop-in 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.

DPMS Delta Pak barrel spring, barrel spring ring and 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.

  • Magpul MBUS front and rear flip-up sights
  • Troy Industries folding sights

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

Cheaper Than Dirt-branded AR-15 lower receiver
Building your own AR-15 is very satisfying.

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.

  • DPMS compensator
  • Primary Weapons Systems compensator
  • Bravo Company BCMGUNFIGHTER Compensator MOD 1
  • Troy Industries Medieval muzzle brake

25. Magazines

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.

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.”

Do you have any DIY ARs? Tell us what your favorite parts are and why in the comment section.

The Mission of Cheaper Than Dirt!'s blog. "The Shooter's Log", is to provide information - not opinions - to our customers and the shooting community. We want you, our readers, to be able to make informed decicions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (35)

  1. I live in California and I’ve built an AR10 and AR15. When you buy a lower receiver parts kit it has the standard magazine release button which is good, but illegal in California and now I think also in New York. To be legal, you must also buy a “bullet button” which is a special part for the magazine release that is fairly inexpensive. You can’t use your finger to release the magazine with a bullet button installed – you must use an external tool, such as the tip of a bullet. The ThumBee is a tool that attaches to your thumb and allows you to quickly and easily drop the Magazine and, because it is an external tool it is 100% legal. Google ThumBee to learn more about it.

  2. Agree that a few favorite parts were omitted
    (Geissele triggers are awesome)

    Ranier Match grade barrels are actually made from Shillen w/ ratchet rifling for a fraction of the cost.

    SLR adjustable gas block for any build for 300 BLK if going to run super/sub sonic and or suppressed-great addition

    Couple other mentions that are needed before anyone sets off building:

    Good reference materials-“The Ar-15 Complete Assembly Guide” by Kuleck and McKee is excellent.

    Completely agree with previous post that it Really should have a list of tools:
    Torque wrench/ barrel nut wrench
    Armorers tool (buffer wrench)
    Roll pin punches
    Armorer hammer
    A front take down pin tool is a great cheap tool
    Lower and upper receiver vise blocks
    A good bench vise
    Good graphite free grease (like Aeroshell 33)
    These are not complete like front sight block for roll pin in gas block etc.

  3. What about the trigger guard? Most complete build kits omit this, because a few lower receivers have one milled in place.

    And I’ve never seen any partial kit include one.

  4. You don’t mention the gas piston systems available. They increase reliability and it sure is nice not to have to clean all that carbon crap that builds up in the bolt and carrier.

  5. Way to go guys, recommend a barrel that is out of stock and can’t be back ordered! Good advice lol. Best way to move product, make you go somewhere else to get it!

  6. Very good little article but never really thought about what my favorite part is on an AR. Anyway, I am remembering back when I first built an AR (and I do still work on them). That which I could have really used was a tool list.
    Tools that a person would need to properly assemble, and disassemble this style of rifle. Would you gentlemen work on that for your readers?

  7. Save me a couple hours of research. Tell me which enhanced AR triggers are compatible with the Wolff extra power hammer spring. Obviously CMC and Timney are out because they have a contained trigger spring, I believe.

  8. This is excellent, and I wish I had had this information, when I built my first AR and had to come up with this information by myself. Although some of the individual components that I like are not listed, the ones listed are a good starting point for someone considering a build. For example, I like Giessele and Timney triggers, First Samco grips, and the Mako GL butt stock.

    A follow up article on a minimum tool kit to facilitate the building process would be useful.

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