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).
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.
- CMMG stripped lowers
- Anderson Manufacturing MIL-SPEC stripped lower
- Del-Ton lower receivers
- Spike’s Tactical lower receivers
- Sharps Bros. lowers
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.
- CMMG complete lower parts kits
- DoubleStar complete lower parts kits
- Strike Industries lower parts kits
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.
- Primary Weapons Systems enhanced MIL-SPEC buffer tube
- Leapers UTG MIL-SPEC buffer tube
- DPMS 6 position carbine MIL-SPEC buffer tube
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.
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.
- VLTOR Weapons Systems low profile gas block
- Yankee Hill Machine low profile gas block
- Bravo Company 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.
- Anderson Manufacturing stripped A3 upper with M4 feed ramps
- CMMG Mk4 upper receiver
- Aero Precision upper receivers
- Midwest Industries Upper Receiver
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.
- UTG standard charging handle
- Radian Raptor-LT Ambidextrous charging handle
- Bravo Company Gunfighter ambidextrous charging handle
19. 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.
- Magpul CTR carbine stock
- Mako Fab Defense AR-15 buttstock
- Leapers UTG A2 style fixed stock assembly
- Adaptive Tactical EX Performance adjustable 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
- Leapers UTG handguards
- 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.
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
- Aim Sports AR 45 Degree Flip Up 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
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.
- Tacfire Steel Muzzle Brake
- Leapers UTG A2 flash hider
- Bravo Company GUNFIGHTER Compensator MOD 0
- 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.
- SIG Sauer Romeo5 X red dot sight
- Firefield Impact XL Reflex red dot sight
- Aimpoint sights
- Leupold Scopes
27. Extras
“Extras” include things such as sling mounts and attachments, vertical grips and tools.
- Magpul MS4 sling
- Magpul sling quick detach mount
- Magpul AFG foregrip
- AR-15 tools
- .22LR conversion kits
For instructions on how to install these parts, watch these videos from “Building Your AR Lower Receiver.”
Things sure ain’t what they used to be. The cheapest stuff linked on this article adds up to over $1100 – no sling, no optic, just one mag. Why bother? I can buy a complete rifle and have a blast taking it apart and putting it back together for half the price! I guess inflation hits the DIYer 27 times harder when the real problem is nickle and diming.
I have been building AR’s since early 1980s .put your cash in the BCG and if you are going max accuracy the the barrel as well a heavy 20-24″ fluted or such other than that the AR15 is mil spec parts and extremely modular totally interchangeable, its really easy awesome fun and when you got a 1″ group at 300 yards you did it with your hands.
Having built 3 lowers and to discover this video on how to install pivot pins using a nex wrench was awesome! Wow! How much time I would have saved not having to crawl around on the floor looking for pins and springs! Now, I need to build another!
I like that a list of quality components were included in this article. Just remember, don’t go cheap on your bolt carrier group. I am a gunsmith, and several customers have come in with AR’s that short cycled. I can think of only one that had a misaligned gas block. The others all had defective bolt carriers. The original mil-spec M16 required a high temp sealant applied under the gas key. Most manufacturers don’t do this. They rely on a good machining job on the key and the bolt carrier. Sometimes they are not smooth enough to prevent the gas from leaking out, and the gun will short cycle. When I get a home-built gun that short cycles, I use the bolt carrier out of my AR, and try again. If that solves the problem, I take the customer bolt carrier apart & seal the gas key with some silicone head gasket sealer. Another suggestion: get your barrel and bolt group from the same manufacturer. I have never seen a headspace problem when they come from the same place.
Little nugget*
If you build a 20” or longer with Rifle length gas tube and a non-adjustable gas block, you will need a rifle length stock and buffer system. If you use a carbine buffer system, you may have cycling issues. It took me several trips to the range to figure that one out.
So far, built a .223 Wylde w/ 24″ barrel, .223 Wylde 18″ barrel, 5.56 16″, 5.56 left handed (for my wife), 9mm 16″, .308 AR10 20″, and a 7.62×39. It is fun to take you time and determine what you want it to be when finished. Also, very gratifying to know you did it.
I really appreciate this article. Too bad it wasn’t written 3 years ago when I was doing my first build.
I’ve assembled several AR’s now, and as a former race engine builder, I’ve found that ARP assembly lube is ideal for the barrel nut installation. It’s a moly based grease, but with added anti-seize and high temperature components. It’s specifically formulated for threaded fasteners in high torque/temperature applications. Also, Ford has a web page for torque values when adapters are added to a torque wrench. Select your configuration from several types, plug your values in & the corrected value is displayed.
http://www.fordservicecontent.com/renderers/torquewrench/wrench_formula_main_en.asp
I got the bug and built my first AR…actually just the lower because I don’t have all the tools. Was fun. But now I want to do another one….almost *** more fun than shooting because you build it with your hands.
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.
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!
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.
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.
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.
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.
Good article. I would add that if you buy an 80% lower and finish it yourself, you have a rifle that is all yours. It is rewarding to do so and a lot of fun too. I built three black rifles this way.
I see this article was reposted today…6/21/16, and there are a bunch of replies going back into 2014 which tells me its an older write up. I like most parts included as i tend to go upgrade on several key areas ie…bcg, stock, backup iron sights and handguards. Ordering parts separate with all the different shipping can cost more than a complete factory build however….i like palmetto state armory, primary arms, joebob outfitters and of course ctd. Dont forget skd. Anyway, there is alot of value and experience gained from building your own versus buying one complete. So weigh that out. In todays climate….get one while you can for sure, because come november….who knows. Hope this helps you make an informed decision.
Very true. When I updated the links links, I changed a few features, including the title and brought it back to the forefront by republishing it. ~Dave Dolbee
The Fab Defense Butt Stock in the Picture costs $199.99 and will Carry ANY M4 Magazine in the “Spare Mag” Slot…
Almost all of the links on this article are broken. Most of them just take you to the cheaper than dirt home page rather than the product page like it should. Other than that this article helped me figured out what is needed and what parts i might want to buy.
Thanks for this article
Zach,
Thanks for the heads up. I went ahead and updated the links and a few features of the article. Some of the links were just old and a few did not convert when we launched the new site. ~Dave Dolbee
Great summary helps me a lot since I’m new to ARs but one thing you should mention on the part about the stripped lower is that you need to be 21 to buy a stripped lower I found that out after doing tons of research on what I want to build
Can anyone guess how much, ballpark, it would cost to make a basic ar15? Doesn’t need to have fancy parts. I’m just trying to get an idea of overall costs. Thanks in advance
I can’t guess, but I can tell you from experience. A basic M4 style AR-15 in 5.56 with a flat-top receiver and standard military grip, buttstock and handguard can be built for well under $525 if you shop intelligently. You’d need to add a rear sight, of course and that will run you something in the neighborhood of $30-$60. For your first build, put together a lower and buy a complete upper and slap it on. Keep in mind that for a complete build (both upper and lower) there’s going to be a modest investment in tools. If you’re only going to build one, think twice before doing a full-out build.
These are the parts which I like as I feel they make ar-15 more accommodate nearly any shooter comfortably:-
Wilson Arms barrels, ER Shaw barrels, Daniel Defense, Magpul, Smith & Wesson, Daniel Defense, DPMS, CMMG and more. We carry butts tocks, Carbine length handguards, Rifle length handguards, parts kits, pistol grips, Barrels, rear sights, complete uppers, vertical grips, Magazines, specialty barrels.
This is a complete list of everything you need to build an AR-15 rifle.From overall design to material composition, everyone wants to offer the best that a gun could ever be.
Best rifle is one with no serial number. Using an 80% lower, no FFL required, no 4473, a router, jig and some time. If you’re moderately decent with tools most anyone can build one.
Untraceable. No serial number.
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.
Anyone built a 300 Blkout using an 80% complete frame? Please share your info….:-))
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.
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.
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.
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!
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?
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.
Sorry. I meant contained hammer spring and hammer.
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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