Tuesday, March 8, 2022

We Have An AR At Home, Part 7: Final Assembly and Tests

We’ve finally assembled our lower receiver, upper receiver, and all the rest at last. Now we can take it out to the range for a test fire, right? Well, not quite.

There’s still a little bit of final assembly to do first, and once that’s complete, there are some function and safety checks that need to be done before we get to the shooting part. Don't neglect these! They are an essential part of any build.

At this point we should have the following elements:

  • Complete lower receiver
  • Complete upper receiver
  • Charging handle
  • Bolt carrier group
  • Recoil spring and buffer weight
  • Magazine
  • Dummy Rounds (optional)

Bolt Carrier Group Checks
As discussed in a prior article, there are some things to check on the bolt carrier group, specifically the staking of the gas key. Confirm this was done properly before proceeding.

The bolt and cam pin also need to be lubricated prior to firing.

  1. Disassemble the bolt carrier group and put a couple of drops of oil on the bolt body and the cam pin
  2. Make sure there’s an even coating of oil on both parts, then reassemble.

Rifle Assembly
  1. With all components at hand, start the charging handle into the main part of the upper body until the small wings on the charging handle can pass through the notches into the channel in the top of the upper.
  2. Make sure the bolt is in its full forward position in the carrier, then align the gas key with the slot in the charging handle and push them both forward until they lock in place.
  3. Combine the recoil spring and buffer weight. They may be a snug fit; if so, twist the spring against the buffer opposite the coil direction so it slips into place.
  4. Insert the spring into the buffer tube and push the buffer weight past the retention pin. The pin should hold the buffer in place.
  5. Make sure the ejection port cover is closed for this next step. This way it can’t be pinched between the upper and lower receivers and possibly bent. 
  6. Extend the forward pivot pin and the rear disassembly pin on the lower receiver fully to the right and position the upper receiver in place. It will likely be necessary to pull backward slightly on the upper against the resistance of the recoil spring.
  7. Push the pivot and disassembly pins through completely until they click into place.

The rifle (or carbine) is now assembled and ready for function checks.

Safety Check
  1. Pull back and release the charging handle to confirm the hammer is cocked. 
  2. With the safety in the safe position, pull the trigger. Nothing should happen.
  3. Release the trigger, flip the safety to the fire position, and pull the trigger again. The hammer should drop. This should be both audible and tactile.

Trigger & Disconnector Check
  1. Keeping the trigger held, pull back and release the charging handle again. 
  2. Slowly ease the trigger forward until another audible and tactile click occurs. This is the hammer switching from the disconnector to the trigger sear. 
  3. Pull the trigger again to make sure the hammer falls.

Miscellaneous Checks
  1. Insert an empty magazine and pull the charging handle all the way to the rear. The magazine follower should activate the bolt hold open.
  2. Remove the magazine and press the grooved pad on the upper half of the bolt release. The bolt should slam forward to the fully locked position.
  3. This next one can be challenging: Pull the charging handle back part way and ease it forward so the bolt doesn’t quite close all the way. Gently press the forward assist until the bolt locks forward.
  4. If dummy rounds are available, load two or three into the magazine and cycle them through the action. The dummy rounds should feed, extract, and eject without issue.
  5. When firing the rifle for the first time, only load two rounds in the magazine just in case the hammer slips off the disconnector under recoil. Do this a couple of times to confirm proper function.
  6. Once this test is passed, the rifle can be fired for accuracy and the sights or optic adjusted. But that’s a story for another day.

And now we have a complete AR-pattern rifle fully assembled, checked, and ready to go.

Shoot straight, and shoot safely. 

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