AR15 Lower receiver assembly guide

[Wallace's]

With a small piece of painters tape on the end of an extended 3/16 hex key, I install the grip screw by hand turning until tight. The painters tape holds the screw for easier installation. The same concept works for the flat head cap screws found in many build kits as well. Note: If your grip did not come with a lock washer or Loctite pre-applied, using a small drop of blue 242 Loctite will help hold the screw in place, although a lock washer is what the TM calls for. Tighten until snug.

Ensure the grip remained seated fully after tightening the grip screw. Some grips/receivers may have a very tight fit before the grip screw is installed. It may feel like the screw is “tight enough” yet the grip is still not seated fully. You can check for this by firmly grasping the grip after the screw is tightened, and checking for front and rear wobble. If any is present, re-seat the grip and re-tighten the grip screw. You should have little to no gap along the two noted red lines for most grips if installed properly.

Flipping the receiver back over on the vice block, I now stake the castle nut in two places (per the TM). Using an automatic center punch, I will swage part of the end plate into the notch on the castle nut. It may take 10+ cycles of the center punch to get the appropriate stake. Cycles may vary depending on how strong your auto-center punch is. This can also be done with a hammer and non-auto center punch. Much more care must be taken though to not damage any components though.

Process is repeated for the second stake location.

Install the stock by sliding it onto the receiver extension. It will stop until you pull up on the adjustment lever (if installing a plain M4 stock), or by lifting the lock bar on the below Magpul example.

 

[Wallace's]

Although the Magpul instructions say to lift this lock bar by pulling firmly with your fingers, I have found using light pressure with a flat head screw driver is MUCH easier and will not damage the stock. Lift up (down if your receiver is right side up) on the tabs, then slide the stock onto the extension at the same time.

Although this is not necessary, you can lightly coat the buffer and spring with CLP if you desire before installation.

Seat the buffer into the spring with the spring pushed to the shoulder of the buffer. With the hammer in the cocked position, slide the buffer and spring into the receiver extension, spring first. Fully insert the spring/buffer until the buffer is retained by the retainer. Do not dry fire the lower. Release the hammer, guiding it forward by hand.

The fully inserted buffer and spring will look like this once installed.

You can now lightly oil the sear contact point and FCG pins with a small amount of CLP. If using an aftermakret, non GI FCG, refer to the manufacturers recommendation for proper lubrication.

The receiver is now finished and ready to be mated with an upper receiver.

 

[Wallace's]

Ok, well uploading all that took FOREVER!

I am hoping this helps someone through their first build or shows someone an easier way to assemble a lower than they have been.

 

[ATLDude]

Wow, awesome write up. Much appreciated!

IN for the PDF

 

[EVILWS6]

Nice write up. I'm sure it will help out people.

 

[Wallace's]

Wow, awesome write up. Much appreciated!

IN for the PDF

Thanks, I am still trying to fix the resolution issues on that tool layout image. My laptop is being a little bitch at the moment (although its probably just ESTO → Equipment Smarter Than Operator).

 

[FatBack77]

Ok, well uploading all that took FOREVER!

I am hoping this helps someone through their first build or shows someone an easier way to assemble a lower than they have been.

Awesome tutorial!

 

[01coltcolt]

Excellent instruction Thread! I will refer many folks to it.

 

[STONEWALL]

Tag. Thanks

 

[Ex313]

If there were an Academy Award for "Best Detail in an Instructive Post", you'd be the nominee.

Awesome job!