DIY ARs — Building Your Own AR-15

By CTD Blogger published on in Firearms

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

If you have questions, please sign in to CheaperThanDirt.com and click the “Live Chat” button at the top of the page. Our product specialists will help you with your build.

Happy building!

1. Stripped lower receiver

Stripped lower receiver (the firing part) of an AR-15.

The stripped lower receiver is the serial numbered part of the firearm.

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.

5. Selector

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

CMMG ambidextrous safety selector

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 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 stock.

Buffer spring and buffer tube for an AR-15 rifle

The buffer tube holds the buffer spring and buffer.

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.

M4 barrels

13. Barrel nut

The barrel nut holds the barrel to the receiver.

LBE Unlimited

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.

15. Upper receiver

The 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. 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.

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

AR-15 stocks are either A2 fixed or collapsible.

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 place your to 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, and 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, many people buy them purely on their aesthetic value.

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.

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, but may allow muzzle brakes. Check your local laws before ordering.

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.”

Have you built your own AR-15 rifle? Tell us what your favorite parts are and why in the comment section.

Product pricing and availability are as of time of publication and subject to change without notice at any time.

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Comments (32)

  • Allen

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    Good list. Also one of the simplest and easiest ways to get a fairly custom Ar15 is to buy a complete upper and complete lower separately. All you have to do then is pin them together, and you’ll usually save money over buying a basic stock rifle.

    Reply

  • g sloan

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    i did my first build a few months ago, which is my first AR. I built it out from a stripped lower and added all the ambidextrous components, for us lefties. I did want to experience the upper build but I deferred and purchased a complete BCM upper, with BCG and ambi charging handle, in 300 blackout. Favorite part? I’d have to say, I like the octagonal shaped alpha rail, and the geissele 2 stage trigger. My suggestion for those interested, find a local shop where you can buy much of your parts, or do some homework and bundle your internet purchases to save on shipping!

    Reply

  • GWDean

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    The very best solution to an excellent .308 rifle, for an exceptional price, is just purchasing a Ruger Precision Rifle off the shelf. Building an AR style .308 will run nearly double the price of the Ruger. The Ruger is a sub-moa rifle out of the box, with match ammunition.

    Reply

  • Travis

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    I am interested in a 308 build; something I could piece together over time so I don’t end up divorced for dropping $3000 at once. Who do you guys recommend? It would be for deer hunting. Something with good long range capability.
    Thanks.

    Reply

  • BIG JOE

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    Your first AR-15 build is lots of fun and you will learn a lot. If you want a budget build then you can’t substitute all those parts and come in under budget. I just finished a budget build in February. Total cost was $536.00.
    Not including a cheap scope I had in the safe and a stock sling that I used.
    I agree build the complete lower then shop for a complete upper when you see the one you want buy it. Watch YouTube there is lots of info on there not all good. If you add a Timmeny trigger and an Acog scope you could have purchased a complete new Colt 6920. 1000 rounds of ball ammo and 10 Pmags. Shopping for quality parts at the right price is the key. As far as tools you really just need a brass hammer and some punches. I would recommend a vise block. You can sped a lot on tools you don’t have to have. You can buy a punch kit for ARs for $40. You don’t really need it, but that’s up to you. Take your time and have fun.

    Reply

  • GWDean

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    ARs are like Harleys, you can start out basic or top of the line, but vendors just keep offering new, improved ‘stuff’ that you just have to have. I have a plethora of quality iron sights, red dots, holographic and fixed or variable scopes, with related mounts & reticles. QD mounts, slings, etc It is a never ending addiction, as is the Harley. I thoroughly enjoy building my own ARs, ones for others or just assisting someone else with my equipment or advice, such as it is. I see a new bolt being offered which is selectable for with or without a suppressor. While neat, and quick to select–remove bolt, flip switch, replace bolt, I prefer a much less expensive method–adjustable gas blocks on all my builds. It’s the little things which make everyone’s rifle personal.

    Reply

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