Step By Step Guide to Installing an AR-15 Lower Parts Kit

Step By Step Guide to Installing an AR-15 Lower Parts Kit

The AR-15 is the most common rifle in America and is a semi-automatic version of the military M16. Today we’re going to discuss how to build one on your own. The AR-15 comes in two sections – the lower receiver and the upper receiver. The lower receiver of the AR-15 comes in many models and different styles and can be customized with various accessories. It is also the only part that is regulated and considered a firearm by the ATF. Like the lower receiver, the upper receiver can also be customized into different styles and colors. We’ll talk about  assembling an upper receiver in a different article but first let’s cover how to install an AR-15 lower parts kit.

Magazine Catch Installation

Tools Needed:

  • Lower receiver vice block
  • A punch

AR-15 Parts Needed:

  • Magazine catch
  • Magazine catch button
  • Magazine catch spring

How to Install an AR-15 Magazine Catch

  1. Start off by placing the receiver on the Vice block.
  2. Then take the magazine catch and insert it in the magazine catch hole on the receiver.
  3. On the opposite side, take the spring and place it over the magazine catch.
  4. Take the button and thread the magazine catch into the button.
  5. Press the button in and screw the magazine catch down as far as you can by hand.
  6. Take a punch and press the button all the way inside the receiver.
  7. Continue to screw the magazine catch in until the button is flush with the magazine catch.
  8. Take the receiver off the Vice block and insert an empty magazine into the receiver.
  9. Ensure the magazine locks in place.
  10. Press the mag release button.
  11. Ensure the magazine easily slides out.

Bolt Catch Installation

Tools Needed:

  • Lower receiver vise block
  • 5/64 Allen wrench
  • Ball-peen hammer
  • Roll pin punch
  • Lubricating oil

AR-15 Parts Needed:

  • Bolt catch
  • Bolt catch plunger
  • Bolt catch roll pin
  • Bolt catch spring

How to Install an AR-15 Bolt Catch

  1. Ensure the lower receiver is on the Vice block.
  2. Insert the magazine catch spring into the appropriate hole on the lower receiver.
  3. Insert the bolt catch plunger into the bolt catch spring.
  4. Using an Allen wrench, apply lubrication to the inside of the holes of the bolt catch. This allows the roll pin to slide in easier.
  5. Using an Allen wrench, insert the bolt catch into the lower receiver.
  6. Insert the Allen wrench into the bolt catch to hold it in place.
  7. Lubricate the roll pin.
  8. Using a ball-peen hammer, gently tap the roll pin into the bolt catch hole. Make sure to tap the roll pin in far enough for it to keep the bolt catch in place.
  9. Using a roll pin punch, continue to tap the roll pin into the bolt catch hole. To keep from damaging your lower receiver, make sure that you are going slow and using light taps. This will help minimize damage should you accidentally slip off of the roll pin.
  10. Drive the roll pin all the way into the bolt catch hole until the roll pin is flush.
  11. Test your bolt catch by moving it up and down with spring tension.

Pivot Pin Installation

Tools Needed:

  • Lower receiver vise block
  • Pivot pin install tool
  • Small punch

AR-15 Parts Needed:

  • Pivot pin
  • Detent spring
  • Detent

How to Install an AR-15 Pivot Pin

  1. With the lower receiver on the Vice block, insert the pivot pin install tool into the receiver holes.
  2. Line up the hole on the pivot pin install tool with the hole on the lower receiver.
  3. Insert the pivot pin detent spring through both holes.
  4. Insert the pivot pin detent through both holes.
  5. Using a small punch, press the detent into the lower receiver enough to allow for you to rotate the pivot pin install tool. This will help hold the detent and spring in place. *Do NOT remove the pivot pin install tool. Doing so will cause the detent to fly out under spring tension.
  6. Take the pivot pin and ensure the flat side is facing the lower receiver and the curved side is facing out.
  7. Align the pivot pin with the tool.
  8. Using your fingers, firmly hold the pivot pin tool and the pivot pin in place.
  9. Slide the pivot pin tool out while simultaneously pushing the pivot pin into the holes. This will lock the detent and detent spring into place.
  10. Test the pivot pin by moving it in and out several times.

Safety Selector and Pistol Grip Installation

Tools Needed:

  • Lower receiver vise block
  • Screw driver

AR-15 Parts Needed:

  • Pistol grip
  • Safety selector
  • Pistol grip screw and lock washer
  • Selector spring
  • Selector detent

How to Install an AR-15 Safety Selector and Pistol Grip

  1. Place the lower receiver upside down on the vice block.
  2. Insert the safety selector into the lower receiver.
  3. Insert the safety selector detent into the hole located on the bottom of the lower receiver.
  4. Insert the safety selector spring into the hole of the pistol grip.
  5. Slide the pistol grip over the lower receiver.
  6. Ensure the safety selector spring is inserted into the hole with the detent. Use caution to not kink the spring as you slide the pistol grip on the lower receiver.
  7. Screw the pistol grip down to the lower receiver using the pistol grip screw and lock washer.
  8. Make sure the safety selector spring does not kink as you tighten the pistol grip to the lower receiver.
  9. Once tight, flip the lower receiver over.
  10. Test the safety selector and ensure it snaps in place over the fire and safe modes.

Trigger and Hammer Installation

Tools Needed:

  • Lower receiver vice block
  • Rubber mallet
  • Small punch
  • Lubricating oil

AR-15 Parts Needed:

  • Trigger
  • Trigger spring
  • Hammer spring
  • Disconnector
  • Disconnector spring
  • Hammer
  • Hammer and trigger pins

How to Install an AR-15 Trigger and Hammer

Assemble the trigger group

  1. Take the trigger and the trigger spring and insert the spring over the trigger.
  2. Ensure the trigger spring is aligned correctly.
  3. Insert the hammer spring over the hammer.
  4. Ensure the hammer spring is aligned properly on the hammer.
  5. Insert the disconnector spring into the trigger by inserting the large side of the spring into the small hole located on the trigger.

Install the trigger group into the lower receiver

  1. When the trigger is installed into the lower receiver, the disconnector will go into the groove located on the trigger. The holes located on the trigger and disconnector will need to be aligned once in the lower receiver.
  2. If the safety selector is already installed on the lower receiver, make sure it is on fire mode.
  3. Insert the trigger into the hole in the lower receiver and slide it under the safety selector.
  4. Place the disconnector into the groove of the trigger.
  5. Press down on the disconnector and trigger to align the holes.
  6. Using a punch, insert it into the lower receiver to hold the trigger in place.
  7. Lubricate the trigger pin.
  8. With one hand, press down on the disconnector and trigger.
  9. Insert the trigger pin through the lower receiver.
  10. If needed, lightly tap the trigger pin with a rubber mallet.
  11. Align the spring on the hammer appropriately.
  12. Insert the spring into the lower receiver behind the trigger. The hammer spring will rest on the pin of the trigger.
  13. With pressure, align the hammer hole with the hole in the lower receiver.
  14. Insert a small punch to hold the hammer in place.
  15. If needed, lubricate the hammer pin.
  16. Using pressure on the hammer, insert the pin into the lower receiver, making sure the holes are properly aligned.
  17. Use the rubber mallet to lightly tap the pin into place.
  18. Test the trigger group by pressing down on the hammer until it locks in place.
  19. Set the safety selector to safe.
  20. Using your thumb to keep the hammer in place, pull the trigger to ensure the hammer does not move.
  21. Move the safety selector to fire.
  22. With your thumb on the hammer, pull the trigger and slowly allow the hammer to move forward. If you do not slowly release pressure on the hammer, it can potentially damage the lower receiver.
  23. Reset the hammer and pull the trigger again but do not let go of the trigger.
  24. Reset the hammer and release the trigger. The hammer should be set correctly.

Trigger Guard Installation

Tools Needed:

  • Roll pin punch
  • Ball-peen hammer
  • Allen wrench
  • Lubricating oil
  • Painters tape

AR-15 Parts Needed:

  • Trigger guard
  • Roll pin
  • Set screw

How to Install an AR-15 Trigger Guard

  1. Use a block of wood with tape covering one side to support the lower receiver.
  2. Place the lower receiver on the block of wood so the trigger guard tab is flush. If the trigger guard tab is not supported, there is potential that it could break during installation.
  3. Place the trigger guard into the lower receiver.
  4. Lubricate the trigger guard pin.
  5. Install the trigger guard pin through the lower receiver and trigger guard.
  6. Lightly tap the pin with the ball peen hammer to keep the trigger guard and trigger guard pin in place after removing your hand.
  7. Using a roll pin punch, continue to drive the pin through the receiver.
  8. Ensure the trigger guard does not get pinched while inserting the trigger guard pin.
  9. Continue to drive the pin until it is flush with the lower receiver on both sides.
  10. Some trigger guards require a screw to be installed in the front. If this is the case, make sure to screw it down with an Allen wrench until it’s flush with the lower receiver.

Buffer Tube and Takedown Pin Installation

Tools Needed:

  • Lower receiver vice block
  • AR-15 Multi-tool
  • Hammer
  • Torque wrench
  • Center punch
  • Box cutter

AR-15 Parts Needed:

  • Buffer tube
  • Buffer spring
  • Buffer
  • Catch spring
  • Buffer catch
  • Castle nut
  • Detent
  • Detent spring
  • Receiver end plate
  • Takedown pin

How to Install an AR-15 Buffer Tube and Takedown Pin

  1. Take your buffer tube and castle nut and screw the castle nut onto the buffer tube. The large notches on the castle nut should face the buffer tube.
  2. Place your lower receiver end plate onto the buffer tube. The groove on the bottom of the tube should align with the tab on the receiver end plate.
  3. Place your lower receiver on a Vice block.
  4. Thread the buffer tube into the lower receiver all the way until it starts to cover the hole located on the lower receiver.
  5. Once the buffer tube covers the hole, reverse the tube half a turn.
  6. Insert the buffer catch spring into the hole.
  7. Insert the buffer catch over the spring into the same hole.
  8. With one finger, press the buffer tube catch into the hole.
  9. Using your other hand, turn the buffer tube ¾ of a turn in order to keep the buffer tube catch from coming out of the lower receiver.
  10. Ensure the lower receiver end plate is screwed in slightly past the detent hole.
  11. Insert the takedown pin into the lower receiver.
  12. Insert the detent into the hole in the rear of the lower receiver.
  13. Insert the detent spring into the same hole as the detent.
  14. Using a knife blade, press the spring into the hole to keep the detent spring from kinking.
  15. Turn your buffer tube a quarter of a turn while pressing the lower receiver end plate into the back of the receiver.
  16. Screw the castle nut all the way down and make sure the spring does not kink between the end plate and the lower receiver.
  17. Insert a torque wrench into your AR-15 multi-tool.
  18. Slide the multi-tool over the castle nut and fit the notch on the multi-tool with the notch on the castle nut.
  19. Tighten the castle nut.
  20. Test the rear takedown pin and make sure it snaps in and out.
  21. For added stability, use the center punch to create a dimple on the lower receiver end plate where the top groove is located on the castle nut.
  22. Place your adjustable stock onto your buffer tube.
  23. Insert the buffer tube spring into the buffer tube.
  24. Insert your buffer into the buffer tube spring.
  25. Push the buffer and buffer tube spring into the buffer tube until it locks in place.
  26. Lubricate the takedown pin, pivot pin, buffer catch, safety selector, trigger pin, and hammer.

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