AR15 Upper Receiver Build AR15 Upper Receiver Build:

The following chronicles’s upper receiver build.  It is presented for information purposes only.  Have a certified gunsmith inspect and check any work prior to attempting to fire.




 partners with Brownells to build a top of the line AR15 upper receiver

The upper build begins by selecting the barrel.  The choices in barrels may seem overwhelming at first, but the basics of selection are fairly easy.  I prefer direct impingement guns to piston driven guns, so direct impingement it is.  Barrel length, well that is easy; 16″.  Sight radius is determined by the length of the gas system, rifle (longest) mid length or carbine (shortest).  I selected the carbine gas system. Why?  Because I have spare parts.   Reflecting on my needs,  I selected a Daniel Defense 16″ M4 profile barrel (100-005-853).  Daniel Defense hammer forges, then chrome lines their barrels.  This process yields an incredibly durable product that lasts for thousands of rounds.

The barrel will be installed into a flat top upper receiver (100-005-853), that was included as part of a kit I received from Brownells.  It includes an upper receiver, charging handle, hammer and complete bolt carrier group coated in Fail Zero’s proprietary EXO coating system.  The EXO coating provides a permanent dry lubricity to the treated parts.

Fail Zero EXO Coated Kit

To address the small parts that I will need to finish this build, I ordered a Colt upper receiver completion kit (080-000-607).  The kit contains all of the small parts you need to turn your barrel assembly, hand guards, upper receiver, charging handle and bolt carrier group into a complete upper.  The Colt kit costs slightly more then some of those by other vendors, but you get what you pay for.  In this case, parts from the company who has been building this style rifle for over 40 years.

I start by installing the forward assist into the upper receiver.

Forward assist parts (right). Roll pin holder and punch (left).

I like to start with the pin that retains the forward assist.  Use a roll pin holder to guide the pin and gently tap it in enough to start it.  Be careful not to drive it in to the point where it will impede installation of the forward assist.  I placed the upper on a rubber mat for this operation.

Roll pin holder starts the pin which retains the forward assist.

The spring slides over the forward assist’s body, then insert it into the upper.  If you have an AR with a forward assist, you can reference the inside in order to properly align the forward assist pawl.

Forward assist being inserted into the stripped upper. 

Push the forward assist in the remainder of the way and use a roll pin punch to drive the pin flush.  The use of the proper punch is critical with roll pins, conventional punches can damage the pins and slip off, possibly damaging the parts.  The roll pin punch has a small guide in its center that prevents this from occurring.

The forward assist retaining pin is driven flush.

Next step, install the ejection port cover.  Here are the parts:

Ejection port cover parts. Notice the small “c” clip in the photo below the ejection port cover spring.

Begin by placing the “c” clip into the ejection port cover pin.

The ejection port cover pin has a small recess milled into one end. Press the “c” clip into this recess. Be careful not to drop the clip, it is small and hard to find on the floor.

The remaining installation is simple.  I start by inserting the ejection port cover pin into the ejection port cover.  Once the pin is started, align the spring as shown below and finish pushing the pin through until the “c” clip hits the receiver.  Close the cover and flip it open when you are done.  The cover should be driven open by the spring, if the cover is not under tension to stay open, you installed the spring backwards.

Ejection port cover fully assembled.

Time to prep the barrel for installation.  I begin by removing the front sight base.  This can be a tricky process if your front sight base is installed with mil spec taper pins, this is the case with the Daniel Defense barrel.  To aid in the process, Brownells makes an AR15 front sight bench block  (080-000-252) specifically designed for the task.  I have tried this with standard bench blocks and hockey pucks, this is another case where the right tool helps to get the job done.  Once the barrel is secured in the block, I start the pins with a short replaceable pin punch and then finish driving them out with a standard punch.  Slide the front sight assembly off of the barrel and secure the pins.  I typically keep a supply of small bags on hand to secure parts as I progress along.

Drifting taper pins with the barrel secured in the AR-15 front sight bench block.
Once the pins are removed, simply slide the front sight assembly off of the front of the barrel.

This upper receiver will use a Daniel Defense FSP Rail Interface System II (RIS) in flat dark earth (100-005-809).  Weighing in at 16.2 ounces, the RIS II rail system is constructed of aircraft grade aluminum and coated in military specification hard coat type III anodizing.  It has 12.57″ of rail surface and a cut out to allow a standard front sight to protrude through the rail.  Begin by placing the bolt up plate and the barrel nut onto the barrel.

Bolt up plate (left) and RIS II barrel nut (right)
Note orientation of barrel nut and bolt up plate.

Insert the barrel extension into the upper receiver.  I typically put a light  coat of oil on the barrel extension to help it slip into place.  In this case I am using a light coat of Clenzoil Field and Range.

Insert the barrel extension into upper receiver


Here, the barrel extension is fully seated. Slide the bolt up plate back into place and hand tighten the barrel nut
Barrel nut is hand tight

Now its time to torque the barrel onto the upper receiver.  Begin by securing the upper in an upper receiver bench block.  These blocks are typically equipped with a polymer insert to prevent receiver breakage.

Place the upper receiver block insert into the upper. The ejection port cover will open when you do this. Once the insert is fully seated, close the ejection port cover.
Place the upper receiver into the block and place in a vise.

Once the receiver is in a vise, use the Daniel Defense Lite Rail wrench to tighten the barrel nut.  This wrench is not included.  Do not use a single point steel spanner, you will end up gouging the aluminum barrel nut.  Daniel Defense recommends between 50-75 foot pounds of torque be applied.

The barrel is now attached to the upper receiver.  To proceed, we will need to attach the gas tube to the front sight base.  This requires the carbine length gas tube and gas tube pin, both of which are included in the upper receiver completion kit.

Insert the gas tube into the front sight base assembly.  Note: the gas port is facing down, towards the barrel.


Secure the front sight base assembly in the front sight bench block and set the roll pin with a roll pin holder.  Finish driving the roll pin flush with a roll pin punch.

With the gas tube attached to the front sight base assembly, the rail and front sight can be slid onto the barrel.

Place the front sight base assembly into the slot in the top of the rail and slide both into place.


Lift the rail up slightly and insert the taper pins into the holes. Drive them home with a punch.


Insert the two 3/4″ screws into the bottom of the rail and hand tighten.
Now insert the four 7/8″ screws into the front of the plate and hand tighten.

Once the four screws are installed, verify alignment of the rail and begin to tighten the six screws to between 29-32 inch pounds of torque.  Daniel Defense recommends that you torque the center screws first, then the upper screws and finally the lower screws.

Now you can slide in the bottom part of the rail.

Tighten the four screws that secure the bottom rail to the top.

Installation of the rail is complete.


The Primary Weapons FSC 5.56 is an outstanding muzzle brake.  Even though a 2.23 rifle doesn’t kick much, the reduction in muzzle flip is immediately noticeable.

FSC 5.56 with shim kit

I’ve installed these brakes in the past and indexing them can be tricky.  Normally, alignment is accomplished through a crush washer or a peel washer.  Primary Weapons now includes a “Muzzle Device Alignment Set”, this set includes three different thicknesses of washers, each offering a its own correction of the orientation of the muzzle.

Note the recess towards the back of the brake. This hides the indexing washers shown in the last photo

Since the FSP RIS II rail is so long on this upper, the barrel cannot be secured in the vise using a barrel block.  In this case we will use some rubber lined vise jaws.

Barrel secured in rubber vise pads
Indexing the brake:  adding and/or changing the shims from the kit allow the installer to index the brake in the proper orientation


Install the charging handle and the bolt carrier group and the upper receiver is complete.

The parts used in this project were provided by  All of Brownells products are backed by their 100% satisfaction guarantee.

Fail zero upper kit 100-005-446
barrel 100-005-853
rail 100-005-809
upper completion kit 080-000-607
AR15 fron sight bench block 080-000-252