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Build Your Own AR from Scratch

The AR-style rifle’s modular design allows nearly anyone to build a perfectly personalized gun from the ground up. All it takes is the right components, a few specialized tools and some friendly advice from the experts. So if you see an AR in your future, why not envision, then build, one that exactly suits your needs?

Adaptability—it is likely the foremost reason the AR has become America’s universal modern rifle platform and is unquestionably a serendipitous byproduct of the gun’s modular design and space-age construction. It also meshes perfectly with American shooters’ penchant to own something a little different. When it comes to building an AR from the ground up, modularity means it can be easily tailored from the start, or modified after the fact, to suit the specific, often evolving, requirements and tastes of all manner of users.

In fact, a do-it-yourself build is perhaps the only way to end up with exactly the AR you want. At least that was the conclusion I came to and the reason for this project. My aim here is not to retrace every aspect of the AR-building process in step-by-step fashion—that has already been covered elsewhere—rather it is to suggest how to approach the process and to convey a few of the tips I learned along the way that might make it less stressful the first time around.

I admit that the AR rifle platform had never been my favorite, but even as a lifelong fan of the Garand-based gas guns, particularly the M1A, I could no longer resist the accuracy, parts availability and adaptability inherent in the AR’s modular design, or its long military pedigree. So, I decided that, starting with an ordinary AR flattop upper and standard lower receiver, I would build an all-around rifle suitable for target work, hunting and self-defense—within the limits of the .223 Rem. cartridge. A carbine might have been the more popular choice, but therein lies the beauty of such a project—you build the gun that suits your needs and preferences despite what the masses are doing. Regardless of your reasons for going the built-it-yourself route, however, the first step should be to decide what role or roles you intend the finished rifle to perform. For example, a dedicated close-quarters self-defense carbine will call for an entirely different set of components and design parameters than a long-range varminter. Either choice is entirely valid and easily achievable, though, given the myriad choices in available components.

One company has simplified the process of building your own AR like no other by stocking what is likely the largest selection of AR components—1,500 individual parts from 175 vendors at last count—ever warehoused under one roof. That company, Brownell’s of Montezuma, Iowa, has a nearly 75-year track record of supplying  the gunsmithing trade and consumers with the best available firearm components, tools and advice. And, despite its enviable reputation for old-fashioned customer service, it is not in the habit of getting behind the times. So a few years ago it constructed a dedicated website, ar15builder.com, for the express purpose of allowing its customers to virtually configure their own ARs using its vast inventory of receivers, barrels, stocks, fore-ends and other components. I tried it and found it enjoyable and helpful for learning about the various components, their compatibility and their prices. I also viewed the company’s DVD, “How To Build an AR-15” and read the book The AR-15 Complete Assembly Guide by Walt Kuleck with Clint McKee from Scott Duff Publications. All of that pre-build activity better prepared me to discuss the build with suppliers and to perform the final assembly.

After forming a few gut feelings about the direction I wanted to go with the rifle and jotting a short list of questions, I picked up the phone and called Brownells, asking to speak with one of its more than 14 staff gunsmiths—all of whom, by the way, have built at least one AR. When Mike, a self-described “M1911 man” who had nevertheless built somewhere between six and 10 ARs, came on the line, I proceeded to pepper him with my thoughts, concerns and questions, and he was able to walk me through them in short order.

In completing the build illustrated here, my first, I found one of the most challenging aspects of the process was thinking far enough ahead when selecting specific components so that subsequent choices would be compatible and complementary. Each choice brought with it the somewhat agonizing opportunity to stick with the plan or to deviate for some reason that I may not have considered earlier. As a result, I ordered the parts in three or four separate shipments over a period of several weeks and simply set them all aside in a box to begin assembly at a later date. What you’ll find on p. 72 are descriptive vignettes of each of the resulting subassemblies and/or specific components that I believe lent the rifle its unique identity.

When the time came to assemble the rifle, I found that it went together quite easily because of the familiarity I had gained with its operation and construction by watching the video and reading the book. In addition, all of the parts were delivered as-advertised—properly packaged and complete. I simply took my time and worked only as far as the parts, tools, time and my patience allowed. But when the time finally came to assemble the completed upper and lower assemblies, I realized that any certainty about whether it would hit the mark I had established in my mind would come only after I fired the first shots.

After checking headspace with “go” and “no-go” gauges, I gathered some ammunition and took it to the range where I cautiously fired the first round. I was pleasantly surprised to see that the gun cycled and chambered the second as it should. After shooting a third time I went downrange and was pleased to find a cluster of holes in the target about the size of a dime. There were a couple of failures to fully chamber during the break-in process that followed, but the gun has since run without a hitch and continues to turn in excellent accuracy, particularly with the heavier bullets for which the barrel was designed.

If asked to describe the AR that resulted from this project, I would characterize it as a “special purpose rifle”—compact  and quick-handling enough for short-range self-defense use yet endowed with enough true rifle characteristics for moderately long-range shooting. One unanticipated result, an all-up weight of 12 pounds, 12 ounces, is about the only disappointing aspect of the build. But after the shock of the scale’s revelation wore off, I decided that for a rifle with such a stout barrel profile, quick-release optics, metal back-up sights, a metal fore-end and a bipod the weight was justified—of course that won’t stop me from attempting to prune it a bit by looking into upgrades such as a lightweight integrated optic mount.

In the end, the gun’s overall configuration, features and capabilities are exactly what I sought at the outset months earlier. Although the total build cost—including the scope, rings and bases—was in excess of $3,000, it is in line with fully-equipped top-of-the-line rifles. Plus, the gun shoots well and provides the feel and performance I always wanted from an AR but couldn’t seem to buy outright. Also, the experience of building it from scratch gave me a much greater understanding of the AR’s design and construction and far greater respect for America’s most popular rifle.

LRB Arms Receivers
If there’s one set of components that will have a cascading effect on an AR build, for better or for worse, it’s the upper and lower receivers. Buying from a reputable parts vendor such as Brownells all but ensures that both will be made from properly hardened aluminum alloys by the correct processes and machined to exacting dimensions in key areas. In addition, holes will be free of burrs and finishes will be even and closely matching. Consider that a flat-top upper will allow for greater versatility of the finished product with regard to optics mounting. I had coincidentally ordered receivers directly from the manufacturer, LRB Arms, before the run on AR rifles and parts began. I chose LRB partly because of my high regard for the company’s signature product—hammer-forged semi-automatic M14-type receivers—and partly because I knew that its vendor, JV Precision Machine Co., produces the company’s AR receivers from 7075-T6 aluminum forgings to close tolerances and high standards of quality. Both upper ($110) and lower ($110) receivers exhibited fine fit and consistent finish and showed no evidence of burrs or other manufacturing glitches.

Daniel Defense Barrel & Rail
Not only is the barrel the heart of a gun’s accuracy, its length and weight can heavily influence the entire build. With that in mind, it was the first component I selected from Brownells after buying the receivers. I decided early on to go for a barrel capable of handling heavier bullets, those in the 75- to 77-grain range, having a true 5.56x45 mm NATO chamber accompanied by a 1:7-inch twist rate. One of my Brownells advisors highly recommend Daniel Defense, so I chose the company’s 18" Strength 2 Weight (S2W) model ($279), which I believed would provide a good balance between optimized velocities and reasonable handling and portability. The choice also dictated another fundamental design consideration in building an AR: The barrel’s gas port location and 0.750-inch measurement at the boss for the gas block required the use of a mid-length, rather than carbine- or rifle-length gas system and thus simplified other decisions when it came time to select the fore-end, gas block/front sight assembly and gas tube. The barrel’s stout profile, hammer-forged chromemoly-vanadium steel construction and salt bath nitride treatment inside and out were further assurances that it would likely deliver good accuracy and be durable over the long haul. Its M4-style feed ramps mated perfectly with corresponding cuts in the LRB upper. Because I knew I wanted to mount certain accessories on the fore-end, but was not a fan of the round, extended models now in vogue, I chose Daniel Defense’s Lite Rail 9.0 ($365). It is machined and welded as one piece and free-floats the barrel by attaching to the upper receiver with a special barrel nut, an included spanner and a collar that secures the rear of the unit to a matching flange with six Allen-head machine screws. Its upper rail surface mated nearly seamlessly with the upper receiver’s rail, and it stopped just short of the gas block.

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16 Responses to Build Your Own AR from Scratch

James wrote:
December 09, 2013

Having built many AR's across the cost spectrum, I generally offer just 3 pieces of advice: buy a quality barrel, quality optic and mount, and quality trigger. The rest is all just interchangeable accessories. To go one step further, I advocate selecting the optic for the purpose, then build the rifle around the optic to support that purpose.

Frank wrote:
November 20, 2013

I do not think this article speaks to the average gun enthusiast. Build your own AR for under $700.00 would be more realistic.

Gary Lorenz wrote:
November 03, 2013

I read with interest about this propject. By the time I finished ,well I felt like 'someone' with unlimited funds, and not much experiance fielded this ..'Monster' Over 2K and 12 lbs 5 oz !!!!! with an 18' tube . To his credit he did admit he like M14s. He ought to discover some of the advantages of an AR 15 . The whole article seemed like a project to spend alot of money and come up with ... a whale (not white one) but still. Gary

Jaycen wrote:
October 29, 2013

Check out Intacto Arms they are building custom AR15's that are immaculate. http://www.intactoarms.com/ As well you can grab parts from them.

Kevin wrote:
October 29, 2013

A.R.M.S. Owner has given money to at least one anti-gun politician and sues at others at the drop of the hat.

AMU_Vet wrote:
October 23, 2013

And BTW, its not as hard a thing to put one together custom, as I may have described below. As the author says, Brownells is a good start. You can buy a virtually complete upper from them, very close to your desired specs. Your local FFL dealer can get you a complete lower. Just slap them together. After that, a few custom features to sub out, such as stock, trigger group, or gas block, and your done. Finally, optics of your choice. Piece of cake, with only the slightest of mentoring from someone.

JIMMY CLINE wrote:
October 23, 2013

I HAVE PUT TOGETHER SEVERAL AR-15. R-GUNS HAS A GREAT SELECTION OF UPPERS, AND PALMEADOWS HAS THE BEST PRICES AND QUALITY ON LOWERS. ALL RAN FLAWSELY AND PERFECT.

AMU_Vet wrote:
October 22, 2013

Glen Zediker and Derrick Martin also have some very good books on the subject. Easy and enjoyable to read, also.

AMU_Vet wrote:
October 22, 2013

Reading below, it seems there is indeed a good point to be made here, to address the issue of interchangeability of parts in AR builds (thanks, RJB). And like Jim infers, you can fill a whole book on the topic, in fact several books, to have a full understanding. Reading up will save you a lot of headache, and re-work. I won't try to expound that here, but perhaps point out just a few basic things for beginners, to keep out of trouble and give a feel of what you'll need to know : 1) Jim is right. Other than slapping on a few external accessories, its a good idea to read up on the subject, and at the very least consult an experienced AR builder to mentor with. And you'll need the correct tools to do it. 2) Buy your barrel assembly and bolt complete, to assure proper chamber heasdspace from the factory. If not, have it locally checked with a go/no-go guage, to avoid unpleasant case separations or worse. In spite of good modern machine tolerances nowadays, you still need always check for proper headspace. 3) Shorty barrels are notorious for hard case extractions with max loads. Good idea to always buy an adjustable gas block or tube, to fine tune it when testing. If you don't know this, you'll wrongly blame the manufacturer for 'out of spec' parts, which is not the case. 4) When shopping for parts, always call first and ask the seller if its compatible with your brand of receiver. This is especially true of buffer tubes, barrel nuts, gas blocks, and trigger groups. They'll tell you the right ones to buy. 5) Order your barrel with the upgraded M4 barrel extension, to help avoid cycling problems. 6 ) Be aware of large vs small pin receivers. You may need adapter pins to match them up. Bushmaster is a good source for them. Same goes for buying trigger groups, which come in both pin types. It's an easy thing to order the wrong set because you didn't ask first. 7) Always buy factory matched complete trigger groups. Mix and match is just asking for trouble. You get what you pay for here. Most stock triggers don't have what it takes to let you shoot sub-moa groups. A good high end adjustable trigger is worth its weight in gold. It took a Guisselle trigger I installed for my friend below, to prove the gun could shoot sub-moa. I would have had a much harder time fighting a stock trigger to prove it. Sorry, that's all I have time for, there's lots more than this--hope this helps. Good luck, and yes its very rewarding, and great fun building your own custom gun.

Kwelz wrote:
October 22, 2013

I on the other hand have seen more problems with DPMS than any other company except maybe Olympic arms. Avoid the junk, buy quality. Make the Gun grabbers cry.

Al wrote:
October 22, 2013

I have completed 2 ar-15 in 5.56 and am currently building a 300aac and soon a 6.8spc both for hunting I absolutely love the modular approach of this rifle I have built a lower for each upper but if your on a budget you can have multiple uppers for one lower. Love the platform

RJB wrote:
October 22, 2013

After building several AR variants with parts from a number of different manufacturers, I have had no issues with DPMS parts. The fit has always been perfect with other mil-spec components.

Jim Macklin wrote:
October 22, 2013

MilSpec is OK, essential if you're selling to the Pentagon. But there are better barrel steels, better alloys and surface treatments. If all you want or need is a rifle that will shoot $2,000 worth of ammo while you have it you don't need MilSpec. If you want a gun that will shoot $20,000 worth of ammo and 70+ grain bullets, you might need MilSpec. You will want to know what parts are different, such as buffer tubes. I recommend anyone planning to build an AR [[]or even owns one, should get Patrick Sweeneys GUNSMITHING the AR.

AMU_Vet wrote:
October 21, 2013

I've bought 3 replacement bolts from them, no problems with their heat treatment or headspace tolerances. They matched right up to my milspec chamber. I attributed that to tight specs of modern CNC machine tolerances, which DPMS uses. I just accessorized a heavy stainless .308 panther for a friend, and it shot 3/4moa out of the box, at 600yds. I advised him not to ever sell it. Can't say I've had a problem with them at all, over the years.

CountryRock2001 wrote:
October 20, 2013

I would advise against using anything from DPMS. They are nowhere near milspec. There are much better parts available.

Sydney wrote:
October 15, 2013

You can also use the product gunstruction to prototype and check fitment etc http://www.ar15.com/gunstruction