Tuesday, March 1, 2022

We Have An AR At Home, Part 6: All the Other Parts

Now that the lower receiver and upper receiver have been assembled, it’s time to move on to the remaining elements. While some of these processes are detail oriented, none of them are particularly complicated.

This portion of assembly is also where a truly specialized tool, an armorer’s wrench, might be needed. I say might, because there are two main forend attachment systems, traditional front and rear forend caps and free float forends and the main difference between these two is how they’re attached to the rifle. 

With the traditional style forend there is a metal cap behind the rear sight block and a spring loaded ring, called the Delta Ring Assembly, on the barrel nut. This is the setup that requires an armorer’s wrench.

Free float forends are only attached at the barrel nut end by a proprietary connector. Most free float sets come with the dedicated tool to install them.

While some people consider traditional easier to install, everyone agrees the free float setup allows for more accuracy potential. This is because no matter how the person firing the rifle pulls, pushes, or squeezes the forend, it doesn’t affect the barrel.

So without further ado, let’s get to work.

On top of the barrel extension (the part opposite the muzzle) there’s a small pin. This is called the locator pin and aligns with a notch on the upper receiver.

  1. Place the upper receiver in the vise block and secure in a vise.
  2. Insert the barrel extension into the upper receiver, making sure the locator pin is positioned in the notch. This should be a snug fit.
  3. Apply a small dab of lithium grease to the upper receiver threads.
  4. Slide the barrel nut over the barrel and align with the upper receiver threads.
  5. Using either the armorer's wrench or manufacturer supplied tool, tighten the barrel nut to hand tightness. 
  6. Loosen the barrel nut and tighten again. This is to take up any slack in the fittings.
    • If using a traditional barrel nut, adjust so there is a clear path between two of the teeth for the gas tube.
    • If using a free float barrel nut, follow the manufacturer's instructions for fitment.

Gas Block and Tube

There are a few different ways to install the gas block and gas tube. What follows is my personal preference:

  1. Insert the closed end of the gas tube into the gas block.
  2. Make sure the large port in the gas tube is facing down.
  3. Align the cross pin holes in the gas tube and gas block.
  4. Using a proper size roll pin punch, gently tap the roll pin through until its flush on both sides.

There are two types of gas blocks: those that use set screws, and those that use taper pins. The set screw type are much easier to work with, as the taper pin style requires drilling precise holes in the gas block casting and grooves in the underside of the barrel. For that reason I will only be discussing a set screw gas block here.

  1. Start the set screws in the gas block, but make sure the barrel channel is clear.
  2. If using a traditional style forend, insert the front handguard cap first.
  3. Slide the gas block over the barrel and guide the gas tube into the upper receiver.
  4. The gas block should be firmly against the shoulder of the barrel.
  5. Carefully position the gas block so it’s upright in relation to the upper receiver.
  6. The gas tube needs to enter the upper receiver as straight as possible! Any deflection can cause function issues.
  7. Tighten the set screws fully, alternating from one to the other.
  8. Check the gas block and tube alignment regularly.

Because there are two main types of forend, I’m going to detail their installation individually.


  1. Insert the front of the top or one side forend half, as appropriate, into the handguard cap aligned with the gas tube.
  2. The Delta Ring spring is stout, so this might take some effort.
  3. Pull back the Delta Ring until the rear of the forend clears, and  then press down until the Delta Ring snaps into place.
  4. Repeat with the other side of the forend.
  5. Make sure the Delta Ring has cleared both forends.

Free Float

  1. Read the forend manufacturer's installation instructions.
  2. Slide the forend over the barrel and position it on the barrel nut. This may be a very tight fit!
  3. Depending on the forend style, there may be a wedge on the underside and anywhere from two to eight set screws.
  4. If using a flat top upper and a railed forend, make sure the rail lines up between the two parts.
  5. A rubber or rawhide mallet can help with minor adjustments.

Muzzle Device
For proper timing of a muzzle device, a spacer is needed. Originally, a disk made of compressed layers of foil called a peel washer was used; these could be challenging to work with, and have been replaced lock washers. The current standard is called a crush washer and is fairly simple to use.

  1. Place the crush washer on the muzzle, outward bevel first.
  2. Screw on the muzzle device to hand tightness.
  3. If the muzzle device needs to be timed, such as an A2 flash hider, check for proper positioning.
  4. If necessary, remove the muzzle device and using either a stone, diamond hone, or fine sandpaper, remove a small amount of material from the outer bevel of the crush washer.
  5. Wipe off any metal filings and check fit regularly.
  6. Once the fit is close, it should be possible to thread the muzzle device down until properly timed.

At this point, we should have a complete lower and upper. In the next installment I’ll discuss some final checks and completing the assembly. 

In the meantime, keep your powder dry.

PS: I just realized that I forgot to include instructions on how to  install a collapsible butt stock in my lower receiver post. This oversight has been corrected. 

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