I was reading (Nick’s) post on assembling an AR lower assembly. It was awesome and the associated video answered all my questions and was done very well. All fan boy aside, I was wondering if he could do one for putting together an upper.
I’ve been avoiding doing this one since putting together an upper receiver can be a real pain in the butt. It requires some tools which I don’t have readily available (and probably wouldn’t work in my apartment), but thankfully Tyler Kee offered to give me a hand and show me how it’s done over a few beers in his garage.
Step 1: Forward Assist
Some upper receivers don’t come with a forward assist, but for those that do you’ll need to pop it in. The whole assembly is held in place by a roll pin, and relatively speaking this is the easiest part of the whole process.
Configure the forward assist as shown. The flat side of the forward assist should be positioned towards the outside, while the somewhat curved section should be on the inside. You’ll notice that there’s a recessed section cut out of the forward assist (on the side facing the bolt carrier) — this is where the roll pin will sit and keep the assembly from either popping out or going in too far.
Place the assembly inside the housing. When the forward assist assembly is properly lined up you should be able to see daylight through the roll pin hole. At that point simply take a hammer and bash in the pin. I recommend giving the forward assist a bit of a jiggle every now and then while driving in the pin to make sure that the recessed area is perfectly aligned with the roll pin and nothing is binding.
Step 2: Dust Cover
The dust cover is a bit of a pain in the butt, and the reason is the spring. It needs to be positioned so that it applies force to the dust cover and keeps it out of the way while firing, and getting the spring to cooperate can be a nuisance. The best way to do this is to place the dust cover on the gun, insert the retaining rod halfway, and then place the spring in position using the retaining rod to keep it in place. The long end of the spring should be on the dust cover, while the short end should be on the gun.
Exhibit A: Tyler struggling to get the spring in place. Once complete you should have a functuoning dust cover. Be aware that the retaining rod for the dust cover isn’t held in place with anything — it stays put because the barrel nut that we’re about to put on keeps it there.
Step 3: Inserting the Barrel
The barrel itself on an AR-15 isn’t actually screwed into anything. The barrel is attached to the barrel extension, and the barrel extension is held in place by the barrel nut. The trick is getting the correct torque on the barrel nut to keep everything in place — too much or too little torque can ruin your gun’s accuracy.
For this part, the perfect tool for the job is a Geissele Reaction Rod.Available as part of their armorer’s package, the reaction rod allows the builder to rotate the upper receiver however needed while still keeping the barrel and everything else perfectly still and aligned. Clamp that sucker down in the vice and we’re ready to roll.
The goal is to have the slotted end of the reaction rod sticking out when the upper receiver is placed on the rod. We will be aligning the barrel with the slotted end and then sliding the upper receiver to mate with the barrel extension. There’s a small notch at the top of the upper receiver that will index with a pin on the barrel extension — this is what keeps the barrel from rotating in the gun and allows us to align everything while building.
It is recommended that some lubricant is applied to the reaction rod slotted end before inserting into the barrel. The clearances are very tight here, so it is possible that your barrel extension might get scratched up or stuck. Tyler recommends KG Industries’ Micro Moly Dry lube.
Once the two parts are mated we can move on to adding the barrel nut and locking this whole thing in place. Again, a small amount of lubricant on the upper receiver threads has been applied to make the process easier and to keep the two different materials moving against each other.
Step 4: Installing the Barrel Nut
The barrel nut not only keeps the barrel mated to the upper receiver, but this is where we will be mounting our handguards. It seems like every handguard manufacturer has their own specs and instructions so be sure to follow yours, but I’ll give a general overview to the process here.
The idea is to “time” your barrel nut properly onto the gun. First using your hands to screw on the barrel nut and then a calibrated torque wrench, the device should be perfectly aligned with your gas tube hole in the upper receiver (and square with your top rail) when the proper amount of torque is applied. If this isn’t the case then there are ways to adjust the position of the barrel nut. Some kits use shims, others use screws, but whatever you use there will be instructions provided.
Here, Tyler is trying to install the Kinetic Development Group handguard for the AR-15. I like how they did the SCAR rail and I was looking forward to having one on an AR-15 as well. The barrel nut uses a shim kit, and the nut itself is designed with two sets of threads so that the device can be installed with two starting points 180 degrees off from each other. That all makes it easier to get everything timed, but the problem we ran into was with the provided tool.
That’s not supposed to do that. Having broken the tool we decided to swap to a Seekins rail instead that was easier to install.
Once everything was in place it was time for the final piece of the puzzle: the gas tube.
Step 5: Gas Tube
The gas tube redirects hot gasses from the barrel into the gas key on the bolt carrier group and provides the energy to cycle the action. Preparing the gas tube and installing it is relatively simple.
The first thing to do is pin the gas tube in place in the gas block. The gas block will slide over the barrel and provide the connection between the tube and the port in the barrel. Align the gas tube such that the cut in the side of the tube at one end is aligned with the hole in the bottom of the gas block, and then pin the whole thing into place. Again, Tyler is using another tool from the Geissele armorer’s set to start this pin and I am totally jealous of how easy it makes things.
Once the gas tube and block are pinned together we can move to install them on the barrel. The gas block should align with the hole in the barrel, and the gas tube should feed through the barrel nut and into the upper receiver. When a bolt carrier is placed inside the gas tube should slot into the gas key on the bolt without any complaint.
Aligning the gas block perfectly can be an issue. Tyler says that this is the easiest way — use one finger to block the chamber, blow into the muzzle, and identify when everything is aligned based on when you feel the least resistance to air flowing through the gas tube. It works, but it does look a little wrong…
Step 6: Add the Handguards
Again, this step will be different for every manufacturer. Whether your handguards screw in or bolt in all you should need to do at this point is to affix them to the barrel nut and you’re done.
Step 7: Admire your Work
Or, in this case, your slightly inebriated buddy’s work who did everything for you while you sat around drinking his beer. Which, BTW — 10/10, would recommend.