How-To: Build Your Own Custom AR-15 Rifle

John outside Brownell's

Last summer my son John and I visited Rock River Arms just over the Mississippi River from us in western Illinois. We watched AR-15s being built and got to help test-fire rifles on the range. Having seen it done, we decided to try making our own. This summer we drove an hour the other way to Brownell's, in Montezuma, Iowa, where, with a little adult supervision, we built an AR of our own. Honestly, the savings aren't great if you build your own, but like any do-it-yourself project, it's rewarding. After putting a rifle together you understand exactly how an AR works and you gain a lot of respect for the clever design of this modular, versatile platform. You do save money in the sense that you get exactly what you want to start with, rather than buying a rifle, then replacing a lot of the parts with the pieces you really wanted in the first place. You can build whatever you want, from a prairie dog rifle to a carbine set up to defend your home from zombie invasion. As Brownell's Larry Weeks says, the only rule of thumb is, "Put good parts together to get a good rifle." John and I chose to go the accurate route and built a target/varmint-type rifle with a heavy barrel, custom trigger and adjustable stock. These photos show how we built ours, starting with a pile of parts and ending with a working rifle. Here is John, outside Brownell's, in tiny Montezuma. Now 70 years old, Brownell's has grown from a small gunsmith shop to the producer of a massive 592-page gunsmithing supply catalog.

Starting from scratch

We started with a bench full of parts. The easiest way to build your own is to buy completed upper and lower halves and pin them together, which takes under a minute. We opted to start from scratch.

Multi-Tool

You will need a specialized wrench like this DPMS Multi-Tool for mounting the barrel nut and several other jobs.

Pick your barrel

John screws the barrel nut onto the receiver to fasten the barrel and receiver together. We chose a heavy-contour 20-inch Shilen barrel for accuracy. It has a special .223 Wylde chamber, designed to handle both .223 civilian and 5.56 military ammo accurately. Due to the shape of the chambers and cartridges, rifles chambered for .223 Remington should not be fired with 5.56 ammo.

Secured with a vise

This is Brownell's upper receiver vise block. It lets you hold the receiver securely in a vise without damage.

Support system

You need a big vise for this project. The upper receiver is in the block. I'm sliding in a composite dummy bolt/charging handle that helps support the upper receiver from within. There's also a magazine-shaped block for holding the lower receiver. These two blocks and the wrench shown earlier, are the only specialized tools you absolutely have to have.

The barrel nut

John cranks the barrel nut on. When he's done, it will be on tight and one of the holes in the nut will align with a hole in the receiver for the gas tube you can see in my hand. Pay no attention to the man in the picture (Brownell's Larry Weeks). We did this all by ourselves. Really.

Line it up

Closeup of the gas block, the barrel port, and the gas tube. There's a corresponding gas port in the block that you can't see here. Notice the Sharpie mark we made on the barrel to help line everything up.

Gas tube

I'm fitting the gas tube into the gas block, which has to fit exactly over a gas port in the barrel. Fitting the gas block is the most difficult part of AR building and if you do it wrong, no gases get back to the action to cycle the bolt and you wind up with a single shot.

Tighten the screws

I'm tightening the set screws that hold the gas block on and we're Loctiting them in place.

Check the fit

I'm checking the fit of the gas tube by sliding the bolt up against it. With my finger on the gas tube I can feel if it moves to one side or another when the bolt closes. It if doesn't move, it's centered correctly and I'm good to go.

Forward assist

We're using a hammer and punch to pin the forward assist in place. Some target receivers do away with the forward assist, which is intended to let you manually close a jammed or dirty bolt in the field. NOTE: If you slip while hammering and your punch makes a mark on the receiver, a black Sharpie hides the silver scratch very well. Not that we would know from first-hand experience or anything.

Upper assembly

Here's the upper assembly, nearly completed. Notice we have just installed the forward assist and ejection port cover. Important tip: It's much easier to install the ejection port cover before you put on the barrel. That way, you can slide the ejection port cover pin in from the front. We had to put duct tape on the rear of the upper to protect the finish and push it in from behind, working around the forward assist. Next time we'll know.

Installing Handguard

I screw on the handguard. We chose a free-floated handguard to help this rifle shoot as accurately as possible.

Awaiting bolt

Upper assembly is complete here, only awaiting the installation of the bolt. Our barrel came custom-fitted to its own bolt so we didn't have to check headspace, but normally you would need to check with a go/no go gauge as you installed the bolt.

Trigger guard

From here on out, assembly is quite straightforward. I'm putting in one of the pins that holds the trigger guard. It's designed so you can pop one pin out and fold the guard down for winter use with gloves.

Lower receiver

The lower receiver, whether complete (fully assembled with trigger, safety, mag release, etc) or stripped (just the receiver piece) must to be shipped through FFL holders and requires the same paperwork as buying a gun. All other AR parts can be bought and shipped through the mail.

All the little pieces

Here is the rear takedown pin, the safety/selector, and the trigger. There are little springs and pins not to lose (if your floor is cluttered, put down a sheet or painter's dropcloth to capture anything that falls), but the rifle goes together easily after the upper is done.

The safety

The safety goes in first. Notice the detent spring protruding downward. It will fit into a hole in the pistol grip. The grip is hollow, and screws into the bottom of the lower receiver. The trigger drops in next, and is held in place by two pins. We chose a Wilson Combat trigger for our rifle, for a light, crisp, target-style pull.

Avoid dings

I'm tapping in the trigger pins here. A brass/nylon hammer like this one saves dings on the alloy frame.

Takedown pins

The AR 15 has two takedown pins. Pull out the rear pin and the rifle swings open for cleaning. Pull out the front pin also and the upper comes off. Both pins have detents that prevent them from falling out during emergency field stripping.

Bolt buffer tube

With the takedown pin in place in the rear of the receiver, it's time to put on the bolt buffer tube that holds the spring that returns the bolt to battery. There's a detent and spring that fits into a hole in the receiver and holds the buffer and spring in place in the tube.

Keep it tight

John tightens the bolt buffer tube using the Multi-Tool.

Slide the stock

The stock - a Magpul adjustable - slides onto the buffer tube and bolts into place. Although AR parts interchange you do have to be sure your buffer tube and stock are compatible.

No more rattle

The red rubber piece is called an Accu-Wedge. It fits behind the rear retaining pin to eliminate play between the upper and lower. Before the Accu-Wedge, my rifle rattled. Afterwards, not a bit.

Golden spike

John drives the Golden Spike, tapping in the rear retaining pin that holds the upper and lower halves together. The rifle is done, ready for magazine, sights, then the range.

Snap in the magazine

The magazine snaps in. Yes, the 10-round magazine is boring, unlike the high-speed, low-drag 30-rounders. But, it doesn't get in the way of prone or bench firing, and if you have priced 5.56 ammo lately you know that emptying a 30-round mag can burn up $15 worth of ammunition in 10 seconds.

The finished rifle

Almost four hours to the minute after we started, the rifle is finished.

Ready for zombies

The sight we chose is a Leupold Prismatic. It's 1x with an illuminated reticle, perfect for close combat with zombies, pop cans, and left-over clay targets. This style of rifle deserves, and will eventually get, a traditional variable power riflescope to maximize accuracy.

Sure satisfaction

Shooting a rifle you built yourself is like shooting your own reloads - it adds to the satisfaction. Brownell's is a great source of parts, tools and expertise (check out the "build an AR" video on their website brownells.com) and their site AR15builder.com is a fun way to click and drag parts until you have a parts list for your dream rifle.

Shattered target

John with a shattered Champion VisiChalk target. I know, you can do the same for way less money with a .22 lr, but so what? The AR-15 is so much fun to shoot because the report of the .223/5.56 sounds like it should kick, but it has virtually no recoil and is very accurate. And, you can build it yourself.