How to Build an AR15

Updated on March 10, 2017

Building an AR15 is easy...

I love guns, and I've always wanted to build my own rifle. For most of us, that's an impossible dream - building most rifles requires specialized training, expensive and hard to use tools, and years of experience. The AR15 changes all that. Thanks to its modular nature, an AR15 can be built by anyone with a fair amount of mechanical aptitude, a few inexpensive and easy to use tools, and the ability to follow simple instructions. Building your own AR15 lets you have a rifle set up exactly the way you want it, not how some manufacturer thinks it should be. In my case, I wanted a rifle set up for National Match competition. No one sells one like that except custom gun makers - too expensive for my budget - so I decided to build my own. If I can do it, probably you can too. The only problem is it's really hard to stop at one...

How to build your own AR15 - It's easy with the right tools and info...

Competitive AR15 Builder's Guide
Competitive AR15 Builder's Guide
The Competitive AR15 Builders Guide by Glen Zedeker has everything you need to know about building your own AR15 rifle. The book starts out with a list (and explanation) of the required tools, then progresses through each component group (lower, upper, trigger, etc). It culminates with 5 project rifles, along with explanations of the parts chosen for each build. I would not try to build an AR15 without this book.

Tools You'll Need

It's a lot easier with the right ones...

Some people claim they can build an AR15 with nothing more than a rock, a screw driver, a pair of vice grips, and maybe a roll of masking tape. For those of us who are less talented (or who care about what the final product looks like) a few specialized tolls will be needed...

For the lower receiver you'll need 1/8" roll pin holder and punch for the trigger guard pin, 3/32" roll pin holder and punch for the bolt catch pin, screw driver or allen wrench for the grip screw, pivot pin installation tool (makes this job a LOT easier...), a hammer, small block of wood, and masking tape. The wood block is used to support the trigger guard ear while driving the trigger guard pin and if you don't use it you'll probably break it, ruining a $100 or more lower - SO USE IT. The masking tape is used to protect the lower while driving the bolt catch pin. Even if it's masked though, a steel hammer will ding the receiver if you accidentally whack it, so a brass hammer is better.

To assemble the upper receiver you'll need a strong bench vice, some type of receiver block (I prefer the Geissele Reaction Rod), an armorer's wrench, and maybe a barrel nut wrench depending on what rail or hand guard you're running. The same roll pin holder and punch used for the bolt catch pin is used to install the forward assist.

That is pretty much it... these are all you need to build a high quality AR. I'm not the most talented guy in the world so believe me - if I can put one together with just these tools then so can you.

Lower Receiver

The base of your AR15-style rifle...

The AR15 lower receiver carries the serial number, so you have to buy it through a Federally licensed firearms dealer (FFL). Only a few shops actually make AR15 lower receivers, but they're finished, re-branded, and sold by many companies. When picking your lower, make sure it's forged (not cast) and from a reputable vendor. Also, make sure it's made from 7075 T6 aluminum - a few are made from 6061 which isn't as strong as 7075. I have experience with Rock River Arms, Spike's Tactical, and DPMS. For this build I'm using a DPMS lower receiver because it exactly matches the finish of the DPMS A2 upper receiver I'm using. AR15 lowers can be bought 2 ways - stripped or complete. A stripped lower is just that - a forged chunk of aluminum with no other parts installed. A complete lower has the trigger, safety, magazine release, and sometimes the buttstock already installed. For my build I decided to go with a stripped lower, so I also had to get a lower receiver parts kit (LPK). I got the Rock River LPK from Amazon for $80.

AR15 Triggers

A good trigger makes it easier to control your rifle...

AR15 triggers come in 3 flavors: crappy, match, and 2 stage. Since a poorly done trigger can cause your rifle to be extremely unsafe, it's better to NOT attempt to modify a stock trigger yourself. Instead, buy a drop-in match or 2 stage trigger. My favorite is the 2 stage trigger. Unfortunately for this project I'm on a pretty tight budget and it would have added about $100 to the price of my LPK - so I stuck with the single stage match trigger that was included in the Rock River LPK.

Upper Receiver

The heart of your AR15

I'm building my rifle for NRA Service Rifle competition, so it has to look like a Service Rifle - and that means a carry handle upper. DPMS sells a really nice A2 upper receiver made from forged 7075 aluminum and set up for a National Match rear sight. The upper receiver (in fact all parts except the lower receiver) can be purchased anywhere - you don't need to go through an FFL. I got my upper receiver along with most of the other parts for this rifle through Midway USA.

Upper and Lower set - Matched pair or "mix and match"?

DPMS upper and lower receiver
DPMS upper and lower receiver

Most of the time, any AR15 upper will function with any AR15 lower. A case can be made, though, for buying the same make upper and lower receiver. First, if both parts are finish machined by the same vendor, chances of them fitting and functioning together are increased, even if only a little. Second, even though almost all the vendors claim a "mil spec" finish, they also claim a better finish than their competitors (go figure...) - having both pieces finished by the same vendor helps ensure the same exact finish on both parts, which IMO looks a little nicer. That's why I got a DPMS lower to match my DPMS A2 upper even though I could have saved a little by getting a Spike's Tactical lower receiver.

AR15 Barrels

Lower is the base, upper is the heart, and the barrel is the soul of your rifle...

Barrel selection for you AR15 is important. If you don't have a good barrel, your rifle won't be accurate. Since I'm building a Service Rifle, my barrel needs to look like the barrel on a standard issue AR15. I found 4 class-legal barrels available - DPMS, Krieger, Olympic Arms, and Shilen. Usually when it comes to barrels more expensive equals better accuracy. For this gun though, I went with the cheapest option - DPMS heavy profile (HBAR) service rifle barrel. Normally I wouldn't go cheap on a barrel for a competition rifle, but this particular DPMS barrel has an incredible reputation for accuracy. The only downside is that it wears out faster than the more expensive barrels - 1,000 to 1,500 rounds vs. 2,000 to 3,000 for the more expensive barrels. However, I can buy 3 of the DPMS barrels for the cost of just 1 of the most expensive option (Krieger).

AR15 Handguard Selection

Helping your barrel achieve its best accuracy...

A free floated barrel can really help the accuracy of any rifle, and the AR15 is no exception. A stock AR-style rifle has a handguard that attaches to the barrel at about the midpoint. DPMS, Compass Lake Engineering (CLE), and others make a front handguard that looks just like the stock one but allows the barrel to free float. The CLE unit is reportedIy the strongest. I bought the DPMS unit for my rifle because I was unaware of the CLE unit at the time. If it breaks, I'll probably replace it with one from CLE.

AR15 Buttstock

OK, I'm going to get just a LITTLE political with this one...

Once again, this needs to look like a stock Service Rifle, so I'm using a stock, fixed length A2 buttstock.

HOWEVER... I want to comment on so-called collapsible stocks. First of all, the term collapsible is inaccurate - the stocks don't "collapse," disappear, turn invisible, or make the gun more deadly in any way, shape, or form. A more accurate term would be "adjustable length buttstock" because that's all they do - allow you to adjust the length of pull of the rifle. In spite of what people who hate guns claim, this is an incredibly useful feature and can even make the gun safer to handle and shoot. How? Simple. The better a gun fits the shooter, the easier it is to correctly handle and shoot. An adjustable length stock allows you to make the gun fit you, instead of you trying to fit the gun. It also allows shooters of different sizes to use the same gun. For example, I'm 6' tall and I need a fairly long stock to shoot accurately. My wife is only 5'2" tall and she can't even shoulder a rifle with a buttstock long enough to fit me. An adjustable length stock allows both of us to share a single rifle, and makes the rifle safer for both of us to shoot.

Learning more, every day...

And I thought this was going to be plug-and-play...

I'm building a Service Rifle, so some choices are set by the rules. I f I was building a personalized AR15 I wouldn't be constrained though, and there is much discussion in the AR community about what is "best" or if "best" can even be defined. The two main camps seems to be "everything is the same and if you don't think so you're an elitist" and "more expensive is obviously better so if you can't afford expensive then STHU."

In my very limited experience, both positions are wrong. I'm looking at two lower receivers right now, and though the finish is similar, there are obvious differences. The cheaper one actually looks better (and weighs a little more on my scale , which implies thicker material, which implies stronger...) but they both look like crap compared to SOME of the more expensive offerings... and some expensive offerings don't seem any better than the cheap ones.

I'll stick with receivers today... at the minimum you want forged and 7075. Cast receivers are rare and lots of makers don't say, so stick with one that acknowledges 7075 forged construction. It's the standard, so if they don't say it maybe they're using a lesser material. Also, do NOT get a polymer lower - at least until it's been proven on the AR platform.

Why NOT to build an AR-15...

Sometimes rolling your own is not the best option...

"Your gun is not going to be awesome. Because you don't have the experience to know when a part is correctly fitted to the rest. Your gun will be a piece of junk because you have not been to a serive (sic) or commerical (sic) armory school and learned how to assembly one properly........ worse - you probably do not have the $400 in special tools to do it right. Your gun is going to have so many teeth marks and scratches - you will be lucky to sell the part for ten cents on the dollar."

I found that on Yahoo while researching upper receivers, and my reaction was (and is) what a jerk. He goes on and on in this vein, but his reply to an innocent question does have a grain of truth... the first one you build will probably NOT be "awesome." To say that means you shouldn't build one is stupid though. After all, how do you get experience without doing it?

There are a couple reasons NOT to build an AR-15 yourself though. If you're going to use the gun for self defense, it's better to buy a commercial weapon. If you ever did have to discharge the weapon (or worse, had an unintentional discharge), personal injury lawyers would be all over you and your home built rifle like flies on a cow pie.

Second, don't build it if your reason is to save money. Commercial AR-15 builders make money from selling rifles. You, OTOH, will be buying parts from companies that make money from selling parts. Commercial builders pay wholesale for the parts or make them themselves. You'll be paying higher than wholesale, and if you're buying high quality parts (which you should be), the cost of the parts will easily exceed the cost of a complete rifle from one of the reputable makers.

Finally, if you can't afford to make mistakes - say, mess up a $150 lower - or can't stand the thought of a cosmetically defective gun, building your own AR-15 probably isn't an ideal DIY project for you. If you can live with the risks and limitations though, building your own AR is rewarding, educational, and a lot of fun. I highly recommend it:)

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Please sign my guestbook - I appreciate all comments and suggestions...

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