You’ve come to the most dreaded part of the 80% lower project: Installing the guts of the fire control group, magazine assembly, and safety. Fear not! Below is a detailed, step-by-step instructional guide: How to Install a Lower Parts Kit! We’ll assume you already have your Lower Parts Kit and that you understand the individual parts labelled in the kit.
Tools for Installing a Lower Parts Kit
The following tools are highly recommended for this install:
- AR-15 Roll Pin Punch Set
- Long-Arm Hex Key Set
- Brass Gunsmithing Hammer
- Small rubber mallet
- AR-15 Armorer’s Wrench
- Magazine Vise Block
- AR-15 Build Mat
Step 1: The Magazine Catch Assembly
- Insert the magazine catch into the long hole on the left side of the receiver.
- Place the magazine release spring into the magazine release hole on the other side.
- Screw the magazine release button onto the threaded end of the magazine catch.
- Use a punch to press the button enough to turn the catch clockwise to tighten.
- Continue tightening until the threaded end is flush with the button.
Step 2: The Trigger Guard Assembly
- Locate the trigger guard and two trigger guard roll pins.
- Press the roll pin into the appropriately sized hole at end of the trigger guard.
- Slide the roll pin and trigger guard into the gap behind the magazine well.
- Use light pressure or a small rubber mallet as necessary to seat the guard.
- Swing in and line up the trigger guard’s other hole with the hole in front of the grip.
- Lightly tap the appropriate roll pin into the trigger guard and receiver.
Step 3: The Bolt Catch Assembly
- Locate the bolt catch, bolt catch buffer, bolt catch roll pin, and bolt catch spring.
- Place the spring on the buffer drop the assembly into the hole above the magazine latch.
- Place the bolt catch into the bolt catch area.
- Line up the roll pin hole while pressing the bolt catch onto the plunger and spring.
- Press the bolt catch roll pin into place. Use a punch and brass hammer as necessary.
Step 4: The Trigger Assembly
- Locate the trigger, hammer, trigger spring, hammer spring, and disconnector spring.
- Attach both springs to the appropriate assembly.
- The ends of the hammer spring should be oriented down and in front of the hammer face.
- The ends of the trigger spring should be oriented down and in front of the trigger.
- Rest the large end of disconnector spring atop the trigger in the disconnector spring pocket.
- Place the disconnector into the trigger. The square pocket of the disconnector should rest atop the disconnector spring.
- Place the assembly into the lower receiver, allowing the trigger to pass through the oval bottom.
- Press down on the disconnector to line up the fire control group’s holes.
- Insert the trigger pin through the receiver and fire control group. Use a punch and brass hammer as necessary to seat it.
- Ensure both springs of the fire control group rest atop the trigger pin.
- Apply pressure to the hammer to line up the second trigger pin hole set.
- Insert the second trigger pin through the receiver and fire control group. Use a punch and brass hammer as necessary to seat it.
We’re almost finished! Take a break and come back for Part 2 of How to Install a Lower Parts Kit!