THE UPPER RECEIVER OF AN AR-15 includes the barrel and bolt—the parts of the rifle where the explosion of cartridge combustion is captured and exhausted violently downrange. A poorly assembled upper is dangerous, and can result in injury, or worse.
First time builders: seek the advice of a more experience armorer, or buy a fully assembled upper, which can be shipped to your door, no FFL required. That said, here’s how they’re built:
- Orientation. For our purposes, “left” and “right” refer to sides of the rifle from the shooters perspective when the rifle is pointed forward.
- Work Surface. Make sure you have a clean well-lit area to work. Try our Yoga Mat trick. A drop cloth under your work area saves time hunting for dropped roll pins, too.
- Tools. It doesn’t take tons of tools to build an AR, but these tools are worth the investment.
- Safety. Eye protection is highly recommended. Springs especially like to fly.
|Upper Receiver||Bushmaster 5.56/223 Minimalist|
|Forward Assist||Radian Forward Assist Titanium Raw|
|Barrel||Krieger AR-15 Carbine, .750 diameter, 1:7.7|
|Barrel Nut||Odin Works .223/5.56|
|Gas Block||Odin Works .750-inch Adjustable Low Profile|
|Gas Tube||Odin Works Carbine Gas Tube|
|Muzzle Device||Fortis RED Brake|
|Bolt||Krieger matched JP Enterprises Bolt|
|Bolt Carrier Group||Bushmaster BCG|
|Charging Handle||Radian Competition Raptor|
|Forends||Odin Works 15.5-inch Ragna M-LOK|
|Sights||Magpul MBUS Pro Sights, front and rear|
|Optic||EOTECH Model XPS2 Green|
How to Install an AR-15 Forward Assist
Start by putting the upper in a vise block, then start the roll pin with a pair of vise grips or hollow punches.
Next, put the forward assist spring over the forward assist, and turn it so the flat spot is facing the pin.
Depress the forward assist all the way in, and capture by driving the roll pin home with a brass hammer and ball-end punch.
Because we wanted to make this rifle as lux as possible, we used the Titanium Forward Assist from Radian.
How to Lap an AR-15 Upper Receiver
Lapping is a process of using a gritty clay-like compound to sand away metal material, so the surface is flush and true. The Wheeler AR-15 Receiver Lapping Tool Kit does just this, where the stripped upper contacts the barrel. This is a non-essential step, but recommended for precision builds. To lap an upper, simply secure the upper in a vise.
Cover the lapping bar in lapping compound, and spin it in the barrel slot with a drill on low speed for 10 to 20 seconds. The goal is to take away just enough metal coating until you get down to the shiny aluminum, true, receiver face.
How to Install an AR-15 Barrel
A good quality barrel is essential to an accuracy rifle, which is why we chose a precision single-point cut tube from Krieger.
Single-point cut is the oldest—and slowest—method for rifling a steel blank. It’s considered by many the most accurate. Less than one ten-thousands of an inch is removed from the barrel channel at a time. The barrel is finished after several hundred passes, then hand lapped for peak accuracy.
For this minimalist build, we were tempted to go with a pencil barrel, but leaned in favor of better accuracy, and landed on a heavier Carbine contour with a 1:7.7 twist for good performance from the widest possible selection of bullets.
To install a barrel, make sure the upper is clean. Remove any residual lapping compound and take a wire brush to the threads to ensure there’s no crud left behind.
Next, slide the barrel in place matching the key in the barrel to the notch in the receiver. Slide on the barrel nut and hand tighten.
Once that’s done, break out the torque wrench and tighten it down to 30-foot pounds, or whatever torque your barrel/upper manufacturer recommends. You may need special tools like crow’s feet to do this correctly, depending on the shape of the barrel nut.
How to Install an AR-15 Gas System
A good gas system is the difference between a reliable and a crappy-running AR. For this build, we went with a low-profile tunable block from Odin Works. To install a gas system, first start the roll pin at the top of the block.
Next, install the gas tube so it curves up, and the hole in the tube lines up with the hole in the block. Drive in the roll pin until it’s flush. That’s your gas system.
To install it, run it over the barrel and run the tube into the upper. Ensure everything is lined up, and tighten it down. If the gas tube is tight in the upper, it’s not lined up correctly.
There should be a little back-and-forth play.
How to Install an AR-15 Handguard
Forends or handguards are the first thing most new AR-15 owners change out. It’s very easy to install (or remove one) often only requiring a couple screws (and no springs or plungers!).
For this build, and our 6mm AR-10 build, we chose light, durable and good-looking options from Odin Works.
How to Install AR-15 Muzzle Devices
Muzzle devices like flash suppressors, compensators and cans are also easy to install—about as hard as installing a light bulb. Just sure the crush washer placed with the concave-side faces out.
For this rifle, we went with the tried and true RED Brake from Fortis.
How to Assemble an AR-15 Bolt Carrier Group
We took a standard Bushmaster BCG and broke it down to install a Krieger customized JP bolt that was matched to our barrel. We highly recommend getting a matched bolt from your barrel maker to avoid any potential headspace issues.
Reassembling a BCG is a bit of a puzzle the first time out, but not difficult. Make sure the key is correctly lined up to slot in the bolt.
Next, put the bolt into the carrier and install the key. Turn the key 90 degrees and pull the bolt out. Then slot the firing pin through the back and capture with the cotter pin.
How to Install an AR-15 BCG and Charging Handle
Take the charging handle and slide it in about half way. Then slot in the BCG at a 45-degree angle until it lines up, and slid both pieces in place with a quick snap.
All our rifle builds used the very excellent Radian Raptor Charging Handles. The anodized coating means it runs super slick, greased or not, and the handle wings make it easy to work strong or weak sided.
Rifle assembled, our next stop was engraving and cerakoting. As this rifle came together, we leaned into a race gun styling, with a Stormtrooper white paint job, accented in Range 365 blue.
Nick Kesserling, of FSG Custom, did not disappoint. The R365 logo was etched into the lower. The upper was cut to match the design of the Odin Works Ragna handguard. The cerakote work is impeccable, with the inside of the forend and top rail glowing blue, as if it’s breaking through the white shell of the gun. At the range, its flashy looks have drawn in many admirers.
But does it shoot? Yes it does. This project concluded at the range, when we topped it with a Nikon Black FX1000 4-16×50 scope. We proofed a variety of factory .223 loads and came away with ¾-inch groups from the 73-grain Federal Gold Medal Bergers.
The Nikon was then swapped out for an Eotech Model XPS2 Green holographic sight for close in work, and some night work on coyotes later this winter.
Magpul folding MBUS front and rear Pro Sights were later added for a true co-witnessed setup.