So You Want To Build Your Own AR

Some components that make up an AR-15 rifle.

There’s nothing wrong with buying an AR-pattern rifle off-the-rack complete. Sometimes you just want (or need) something that’s guaranteed to work and is ready to go out of the box. But, if you truly want to make a rifle your own, one of the magical things about the AR platform is the modularity and ability to easily build one that is unique to your use case and needs…

An off-the-shelf complete AR-15 usually represents the mindset of the manufacturer. It could have been to satisfy a request for a reliable law enforcement carbine. It could have been a clone of a military-issued rifle. It could have been a design that the marketing department thought might sell well. In each case, the rifle will most likely work and perform well, but there may be something about it you don’t like. The stock could be a crappy standard-issue one, the trigger could be mush, and so on.

By building your own AR-15, you select the components you want, and can truly make the rifle “yours”. There’s several paths to building your own, some more complex than others, but all within the reach of even a beginner.

Note: I don’t recommend building an AR-15 if it is your first AR. Get one off the shelf and learn from that. For your second AR (and yes, you will want a second Black Rifle! And a third…) you may want to consider building one. It’s a great way to learn.

Lucky Gunner 223 Ammunition

The “Two Pin” Build

I’m hesitant to call this “building” an AR since the process is unbelievably simple, and it is something you are doing anyways if you already own a complete AR, i.e. you are disassembling and reassembling your rifle each and every time you clean it, by popping out the takedown and pivot pins on your AR.

Through this same premise, you can purchase a complete lower receiver, hopefully with the specs and components you desire, and a complete barreled upper receiver (which usually includes a bolt carrier group), hopefully with the specs and components you desire.

The advantage here is that due to the modularity of the AR platform, you can create a brand new rifle, sourcing the lower and upper from different manufacturers if you so wish. You might love how Spike’s Tactical puts together their lowers, but might quail a bit at the price point for their uppers, or just not like the styling. So instead, you source your complete upper from Aero Precision, and boom - two pins pushed and pulled, you have a unique build that hopefully suits your use case. Plus you don’t need any specific tools, like vise blocks, and so on.

The disadvantage here is that you are limited to what each manufacturer offers on their complete upper and lowers, at first. Spike’s might not offer a specific trigger, etc. The Aero upper might not have that specific rail length you wanted. All rectifiable in the future of course, but if you are looking to mix and match and swap components, you might as well just build your rifle from the ground up.

LowerCostBuy Now
BCM Complete Lower$395Buy Now!
PSA Magpul STR$209Buy Now!
BRN-10 Brownells Retro$269Buy Now!
RifleCostBuy Now
PSA 16” Complete$349Buy Now!
Aero M4E1 NO BCG$539Buy Now!

Warning note: If your intent is to build something that is legally classified as a rifle, you cannot legally have a barrel length underneath 16 inches without going through the time-consuming NFA process to make a short-barreled rifle.

Assembling A Complete AR-15 From Components

If you really want to build an AR-15 rifle and truly make it yours, you are going to have to build it essentially from the ground up. The magic of the platform is that most of the parts are commonly available from a variety of sources, and one only needs some basic hand tools, a place to work, and a sturdy vise grip to build your “dream rifle”. If you want a 20” barrel to make a modern precision firearm? You can do it. If you want to make a 16” clone of an M4A1, you can do that too. When you assemble your own rifle, almost any configuration is possible. The starting point, of course, is the stripped lower receiver.

What To Look For In An AR-15 Lower Receiver

A receiver is a receiver is a is receiver, right? Not quite. While after a certain point, you are paying for the brand and maybe some “performance” features like a flared magwell and so forth, you will want to keep an eye on the specifications of whatever lower receiver you are looking at. Remember, in the eyes of the government, this is the “firearm” and when your purchase it, you’ll have to go through the background check process. In other words, if you don’t like your lower, returning it can be a pain, and usually the ancillary costs like the background check aren’t refundable. You might spend $30 on a lower receiver, plus $20 for the background check - then you don’t like it or it’s out of spec. You’ll get your $30 back, but then there’s a re-stocking fee and the $20 transfer fee isn’t refundable. You’ll be in the hole and your rifle isn’t even started yet. In terms of price, the sweet spot for a bog-standard AR-15 lower is usually $60-$100 depending on brand.

What you’ll want to look for in your lower receiver is the following:

  • Lower should be made of 7075 T6 aluminum. What those numbers mean is that the aluminum is alloyed with zinc (7075), and is precipitation-hardened. The T6 is a tempering designation. Any decent lower will be made from this. Polymer lowers are a thing, but do your research. Look for tests and reviews.

  • MIL-A-8625F anodized coating. Unless you’re really going cheap, or getting an uncoated lower for later customization, your basic, bad, black (or OD, or FDE) lower will have this coating.

  • Forged vs billet? Forging hammers the two halves of the lower together, forcing the “grain” into the same shape as the lower. So technically it’s stronger. Billet lowers are cut via a CNC mill into the shape of the lower, so there’s no heating or hammmering to give it that extra .5 percent strength. Billet lowers, however, can be more ergonomic and aesthetically pleasing due to the CNC process. Realistically it’s your choice. Avoid cast lowers. They are rare, sure - but they do turn up, often at ridiculously low prices. Avoid.

  • “Low Shelf”. Manufacturers of lowers will highlight the “low shelf”, which basically is the part of the lower behind the hole for the safety selector. A high shelf lower, the “shelf” will be aligned with roughly the halfway point of the safety selector hole, whereas in a low shelf lower, the shelf will be as low as or a tiny bit below the lower part of the safety selector hole. For day-to-day use it’s basically potato/pot-ah-to but if you’re looking to do a legal conversion of your AR to full-auto, it’s important. The low shelf allows sufficient clearance for a drop-in auto sear component, which, along with some other components, allows for your humble AR to become a real-deal high-speed dispenser of freedom seeds. Most decent lowers are low-shelf.

Of course, other components come into play, like the upper receiver, the barrel, the lower parts kit, the trigger, buffer tube, grip, buffer weight, bolt carrier group, handguard, muzzle devices, and so on. We’ll go over what to look for in those components below.

What To Look For In AR-15 Upper Receiver

The upper receiver is an unrestricted component. You can order one and have it shipped straight to your door. Much like your lower receiver, it should be made of 7075 T6 aluminum, and sport a similar MIL-A-8625F coating. The upper should also sport feed ramp extensions to match with the M4 ramps on your barrel. This helps with reliable feeding of ammunition. Often, manufacturers will sell matched sets to take the guesswork out of things. The top should sport a rail attachment system for your choice of optic, unless you are going retro - then a place to attach a carry handle. Much like with lowers, the best ones come from Aero Precision, Spike’s, Brownell’s, and PSA. Since one of the primary purposes of the upper is to house the bolt carrier group, selection of that is important, as well.

What To Look For In An AR-15 Bolt Carrier Group

The bolt carrier group, aka the BCG, is the heart of your AR-15. It houses the bolt, and the firing pin. Without this in well-regulated order, your rifle is a rather poor club at best. There’s a lot of gee-whiz adamantium-dilithium-beskar (I just gave every nerd reading this blog a heart attack, ha ha) bolt carrier groups, but your best bet is to stick to the battle-proven materials for your build.

  • The bolt carrier itself should be machined from 8620 steel or better. 8620 steel is a hardened chromium/molybdenum/nickel alloy. It’s a wear component so it’s gotta be tough.

  • The bolt carrier should be “M16 cut” or “Full Auto”. No, this doesn’t turn your AR into an M4. Simply put, the full-auto bolt carrier has more mass, for more reliable operation. Plus, other critical components are designed to work with it. You’ll see some “semi-auto” cut BCGs out there. They will work, but can be problematic.

  • The bolt itself should consist of “Carpenter 158” steel, which is a chrome/nickel alloy. Some manufacturers are upping their game to include 9310 steel, which is good-to-go as well.

  • The coating of the BCG should be phosphate, or nitride. Either coating is used in professional applications, and it works. Again, the sci-fi coatings bear looking at, but in a lot of cases they are cost-prohibitive considering the minimal performance gains.

  • The bolt carrier group should be high-pressure tested and magnetic-particle inspected, which is to say it’s been through a process to check for flaws and cracks.

The truth about bolt carrier groups is that very few companies actually make their own. It’s kind of like LED flat panels, there’s only a few plants in the world cranking them out. What you’ll usually see is a manufacturer buy raw BCGs, apply their own coating to them, and maybe a logo, and call it a day. Regardless, there are go-to brands to keep your AR chugging along happily.

What To Look For In Your AR-15 Barrel

An AR is a funny looking thing without a barrel. AR barrel science basically warrants it’s own blog post, so this part will basically summarize what to look for. Note, the basis I’m going for is a working rifle of sorts - something that you can use for defense, etc. Precision barrels basically require a book to talk about. Anyways, here’s what to look for in your AR-15 barrel. For the purpose of this article the assumption is you are building with a 16-inch barrel.

  • The barrel should be manufactured from 4150 Chrome Moly Vanadium steel or similar. It should be treated with a melonite process for wear resistance.

  • The “gas system” should be mid-length, which permits more dwell time for the gas to come back to the receiver and properly cycle the BCG with an acceptable amount of recoil.

  • The feed ramps in the barrel extension should be M4 style. This helps with reliable ammo feeding - basically it makes a longer ramp for the cartridge to go into the chamber. This will match with the ramps on your quality upper receiver.

  • The barrel should, of course, be threaded for a proper muzzle device.

  • Much like your quality bolt carrier group, your barrel should be magnetic-particle inspected and high-pressure tested. The manufacturer will brag about this, and also the barrel itself will bear the mark “MPI/HPT” or some variation thereof.

  • The barrel should have a 5.56 NATO chamber, or a .223 Wylde chamber for the broadest compatibility with ammo.

  • The rifling twist rate should be 1:8 inches or greater, which is to say the rifling makes one twist every 8 inches, or more. A common twist rate is 1:7. This will stabilize pretty much every 5.56mm/.223 cartridge out there.

Of course, you’ll need something to shield your hands from being burnt, namely a handguard.

Note: Unless you plan on doing a pistol build or play in NFA-land, your barrel must be 16 inches or longer for your rifle to remain legal.

What To Look For In An AR-15 Handguard

There’s innumerable configuations and designs for AR-15 handguards. What one should look for is the type of rail attachment system, the length, and the material used to build it.

  • Your handguard/rail should be made from 6061-T6 aluminum. It’s of lower “toughness” than the receivers, but the rail isn’t a wear component or subject to explosive forces - so 6061-T6 is good-to-go.

  • The attachment standard should be Picatinny or M-LOK, which are the two dominant standards in the world right now. Picatinny has been the standard for a few decades now, and Magpul’s M-LOK is coming on strong. You’ll see Keymod, which is also fine, but is not as widely accepted. Adapter segments do exist, so Keymod isn’t a death sentence.

  • The length should be enough to cover the barrel and not expose it to accidental manipulation with your hand. If you have a 16-inch barrel, the handguard should be 12 inches or longer.

  • Avoid polymer handguards. I personally just don’t think they feel “right”.

  • Make sure the handguard is “free-float”, which is to say it is secured to the upper receiver, and not to the barrel. Anything anchored to the barrel can decrease accuracy.

At this moment you have a fancy club. It won’t do much without a proper trigger.

What To Look For In An AR-15 Trigger

We could spend an entire blog artcle on just the trigger alone. In a nuthsell, if you purchased a quality AR off the shelf, it probably shipped with a halfway-decent trigger. You probably won’t “out-shoot” the trigger for awhile. It’s not the gun, it’s you. However, if you are building, you’ll want a decent trigger in there. Some triggers require some work to put in, others are convenient drop-in modules that only require the pins to be pushed in properly. Typically, a decent trigger will be made from similar steel alloys used in other AR components. You’ll want a single-stage trigger, which is to say you won’t feel a “stop” during the trigger press. The standard pull weight is 5.5 pounds. Don’t go above that. The trick here is to not overspend, at first. A $400 trigger will just reveal how bad you are, but precisely. Work up to that trigger.

The Miscellaneous Accessories For An AR-15

We could wax intellectual for hours about a gas block. We could write poems about buffer weights. Stocks are an endless source of debate. I suspect that there’s even essays about pins and springs. We’ll sum all those miscellaneous accessories. They are important, but rather easy to make recommendations on.

  • Lower Parts Kits, aka LPKs. Most manufacturers are conscientious of their brand and will put their logo on a lower parts kit. Not necessarily made by them, but “approved” by them. Geissele, CMMG, Brownell’s - they all offer quality bags of pins, releases, and springs and safety selectors to finish your lower.

  • Buffer weight. Just get an H2 from someone reputable. It’ll ensure your rifle runs well, especially down the road when you throw a suppressor on it.

  • Buffer tube. Make sure it’s mil-spec and made of 7075-T6 aluminum.

  • Stock. I love the Adaptive Tactical EX. Magpul makes some great ones, too. B5 Systems can’t be argued with, either.

  • Buffer spring. Again, same idea - whomever you got your lower/upper from probably sells them, and they work. You can go Joe Exotic and get a Sprinco - they’re cool and last for eons as opposed to centuries.

  • Charging handles are largely personal preference. I like the Radian offerings.

  • Muzzle devices. The A2 that they probably tossed you when you got your barrel will work. If you plan on suppressing, do yourself a favor and buy one that will work with whatever suppressor you have in mind.

  • Gas blocks and gas tubes. Make sure the gas block fits within your handguard and that the gas tube is the proper length for your barrel.

  • Grip. Get a Magpul and call it a day.

  • Some sights and and optic.

  • Magazines to hold the freedom seeds. Just head over to The Mag Shack and load up.

Put Your AR-15 Together

You have your parts. Now you’ll have to put it together. Fortunately the AR-15 can be assembled with common hand tools, and some easy-to-find specialist items.

Things to have:

And most of all - have fun.

80% Builds, 3D printing, What?

True graduate-level AR builders craft their firearms from 80% lowers and 3D-printed lowers. By the letter of the law in most jurisdictions in the US, it’s perfectly legal to build your own firearm from scratch, without government oversight. An 80% lower is an AR-15 lower that hasn’t been drilled out yet. It’s a weird-looking block that isn’t considered a firearm. Thus you can get one shipped right to your door. You’ll need a drill press and a lot of patience.

Polymer lowers are a thing, like I said above - and 3D printers make use of polymer filaments to work their magic. You can 3D print a lower and work from there. However, even more so than with 80% lowers, 3D-printed lowers are highly experimental and require a lot of trial and error to get just right. I wholeheartedly encourage this sort of innovation and experimentation, but with the caveat that your first pieces might flat out just not work.

Build a Bigger AR .308

There’s Nothing More American Than Building Your Own AR-15

We’re a nation of tinkerers and innovators. The true innovation behind the AR platform is that anyone can build one with some hand tools, wrenches, and some time on their hands. Best of all, the finished product is something you can truly call your own. Read up, research, and most of all - have fun!

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