We Have An AR At Home, Part 4: Assembling the Lower

One of the easiest steps to start with is installing a standard magazine catch. This involves three parts: the magazine catch, button, and spring. Use blue painter's tape to protect the anodizing from scrapes.

1. From the right side of the lower, insert the spring and button.
2. Using a punch, hold the button all the way in the receiver and insert the catch from the left side.
3. Rotate the catch clockwise until the threaded portion starts to bear against the punch or the catch bar gets very close to the receiver.
4. When properly installed, the end of the threaded part should be just below flush with the face of the button.

Now that the magazine catch is installed, most of the following steps can be completed with the Lower Receiver Vice Block in place. Place the vice block in the magazine well and secure it in a vice with the front of the receiver facing up.

1. From the left side of the receiver, slide the Clevis Pinthrough the pivot pin ears.
2. Line one of the clevis pin holes up with the pivot pin spring channel and drop in the spring.
3. Place the detent on top of the spring.
4. Using a punch or hex key, drive the detent into the channel until it is completely past the clevis pin.
5. Using the punch as a handle, rotate the clevis pin so it holds the detent in place.
6. Line up the pivot pin with the end of the clevis pin. Make sure the flat side of the pivot pin end cap is lined up with the spring channel.
7. Firmly place a finger in the junction between the two pins opposite the force of the spring.
8. Carefully use the pivot pin to push the clevis pin past the spring channel. 
9. The detent should snap into the slot in the pivot pin. 
10. Make sure the pivot pin slides freely back and forth in the receiver, but is held in place at both ends of travel. 

1. Using a proper size roll pin punch, start the roll pin in the forward bolt hold open lug on the receiver and drive it in just enough to hold.
2. Put the bolt catch buffer and spring together, and insert them into the relief cut in the receiver.
3. Place the bolt hold open over the buffer with the grooved pad towards the top of the receiver. 
4. Use another punch, or a short section of drill rod, to keep the bolt hold open lined up.
5. Using a proper size roll pin punch, gently tap the roll pin the rest of the way through until it is flush on both sides.

For the next steps, the vice block should be repositioned in the vice so the lower has its top facing up.

Fire Control Group

Trigger Assembly

1. Place the smaller of the two-legged coil springs on the sides of the trigger, with the loop under the front of the trigger bar.
2. If necessary, install the disconnector spring in the rear of the trigger bar. The wider end of the spring goes in first.
3. Position the disconnector in the trigger bar with the hook facing forward and the holes aligned. 
4. Use a short section of drill rod, or even part of a toothpick, to keep the disconnector and trigger lined up.
5. Place the trigger assembly in the receiver, making sure the legs of the trigger spring are flexed forward.
6. Drive the trigger pin through until it is flush on both sides.
7. Confirm the trigger returns forward when pulled.

Hammer Assembly

1. Place the larger of the two-legged coil springs on the sides of the hammer, with the loop to the rear and the coil running over the top.
2. Place the hammer into the receiver, making sure the legs of the spring are flexed backwards and rest on top of the trigger pin. 
3. Drive the hammer pin through until it is flush on both sides. 
4. Carefully cock the hammer and make sure it engages with the trigger bar.
5. While controlling the hammer with a finger, pull the trigger to release the hammer.

1. Thread the castle nut all the way onto the receiver extension, notched end first.
2. Followed this with the receiver plate, with the raised portion towards the open end of the extension. 
3. Start threading the receiver extension into the lower receiver.
4. Stop before the extension reaches the buffer retainer relief inside the receiver.
5. Insert the spring and buffer retainer, then screw the extension just enough to catch the edge of the retainer. 
6. Do not rotate the extension in completely or adjust the castle nut yet. 

1. Insert the rear takedown pin from the right side of the receiver, slotted side to the rear. 
2. From the back of the receiver, insert the other detent and spring.
3. Make sure the receiver plate can clear the detent spring, then rotate the extension into place.
4. Carefully push the receiver plate forward, compressing the spring into the receiver.
5. While holding the receiver plate, screw the castle nut firmly into place.
6. Make sure the pivot pin slides freely back and forth in the receiver, but is held in place at both ends of travel. 

For the remaining steps, the receiver can be removed from the Lower Receiver Vice Block. 

1. Place the receiver leftside-up on a firm surface.
2. Position the trigger guard in the receiver with the pass through hole at the rear and the front spring pin locked into the front of the trigger guard opening.
3. Using a properly sized roll pin punch, start the pin into the trigger guard.
4. Confirm everything is lined up, then gently tap the roll pin the rest of the way through until it is flush on both sides.

Safety and Pistol Grip

1. With the receiver still leftside-up, maneuver the safety lever over the trigger bar until it sits flush.
2. Turn the receiver upside down and place the detent point-first into the hole below the safety lever.
3. Make sure the safety lever stays in either the safe or fire position.
4. Place the safety spring into the hole in the top of the pistol grip.
5. Guide the spring against the detent while positioning the grip onto the receiver.
6. Install the lock washer on the grip screw, then place the screw on the proper driver bit. 
7. While holding the grip in place, lower the receiver onto the grip screw and fasten it snugly, but not too tight. 

At this point, the lower receiver is complete and can be set aside while we put together the rest of our rifle.

Stay tuned for more adventures in AR assembly!