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How to Install a Lower Parts Kit: Part 2

We’re back from our intermission! Here’s how to Install an AR-15 Lower Parts Kit: Part 2. If you’re just starting your AR-15 project, go back and check our How to Install a Lower Parts Kit: Part 1 first!

Step 5: Trigger, Takedown Pins, Grip, and Receiver Extension

  1.     Insert the safety selector lever into the safety lever hole on the left side of the receiver.
  2.     Set the position to “Fire”.
  3.    Locate the safety detent and place the pointed end in the hole opposite of the safety indicator.
  4.    Place the pistol grip into the receiver’s pistol grip slot.
  5.    Locate the safety detent spring. It is the shorter and thinner remaining spring.
  6.    Insert the spring into the hole atop the pistol grip.
  7.    Insert the pistol grip into the receiver.
  8.   Insert the pistol grip washer and screw. Tighten with the appropriate hex key.
  9.   Locate the rear takedown pin with spring and detent.
  10.   Place the takedown pin into the right side of the receiver, through to the left side.
  11.   Insert the takedown pin detent into the small hole at the back of the receiver.
  12.   Insert the detent spring into the same hole.
  13.   Locate the buffer tube retainer and spring.
  14.   Place the buffer tube retainer and spring into the hole drilled into the threads of the buffer tube housing.
  15.   Locate the buffer tube and castle nut. Thread the castle nut onto the buffer tube.
  16.   Locate the buffer retainer and place it onto the buffer tube threads so it rests atop the castle nut.
  17.   While pressing the retainer against the receiver and enclosing the rear takedown detent and spring, thread the buffer tube into the receiver’s buffer tube housing.
  18.   Continue threading the buffer tube until the end of the buffer tube is seated just enough to hold the buffer spring retainer in place, while allowing it to be depressed without friction.
  19.   Use the Armorer’s Wrench to tighten the castle nut until it is tight against the receiver.
  20.   Place the front takedown pin spring and detent into the small hole next to the front takedown pin hole.
  21.   Using a thin blade, hold the detent flush against the receiver and insert the front takedown pin into the receiver’s takedown pin holes in front of the magazine well. The pin will lock in place with the detent and spring.

Step 6: Stock, Buffer, and Buffer Spring

  1.       Insert the buffer and spring into the buffer tube, depressing the buffer retainer until the buffer slides past it, resting against the retainer.
  2.       Slide the stock onto the buffer tube.
  3.       Pull the adjustment lever to unlock the retaining pin in the stock.
  4.       Slide the stock into the locking channel of the buffer tube, and release the adjustment lever.

You’re finished!

That’s a wrap! You’ve successfully installed your Lower Parts Kit into your AR-15 Lower Receiver. Now all you need to do is perform a basic functions check of the trigger, hammer, and safety, and mate your complete lower with a full-built upper!


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