How To Assemble an AR-15

© 2010 Nuclear Scorpion Publishing · All Rights Reserved

Assembling an AR-15

Monica Cloud · Victor Brewer · Tony Martinez · Victoria Lance · Chris Sundberg

Table of Contents v

Table of Contents

List of Figures .................................................................................................................................................... vii

Overview .............................................................................................................................................................. ix

Tools You Will Need ........................................................................................................................................... ix

Assembling the Lower ........................................................................................................................................ 11

Installing the Pivot Pin .................................................................................................................................... 3

Installing the Magazine Catch ......................................................................................................................... 3

Installing the Bolt Catch .................................................................................................................................. 4

Installing the Trigger ....................................................................................................................................... 4

Installing the Hammer .................................................................................................................................... 5

Installing the Trigger Guard ............................................................................................................................ 5

Installing the Safety Selector ........................................................................................................................... 6

Installing the Grip ............................................................................................................................................ 6

Installing the Takedown Pin ........................................................................................................................... 7

Installing the Stock and Buffer Tube .............................................................................................................. 7

Installing the Buffer ......................................................................................................................................... 8

Assembling the Upper ......................................................................................................................................... 3

Attaching the Barrel ........................................................................................................................................ 11

Inserting the Bolt Carrier Group and Charging Handle .............................................................................. 12

Installing the Free Float Handguard ............................................................................................................ 12

Pinning and Securing the Gas Block ............................................................................................................. 13

Installing the Flash Hider.............................................................................................................................. 13

Completing Assembly and Operation Check .................................................................................................... 15

Lubricating Your Rifle ................................................................................................................................... 17

Complete Assembly and Operation Check ................................................................................................... 17

Index ................................................................................................................................................................... 19

vi Assembling an AR-15

List of Figures vii

List of Figures

Figure 1: The Pivot Pin in Extended Position _________________________________________________________ 3

Figure 2: The Left Side of the Lower Receiver, Showing the Magazine Catch ________________________________ 3

Figure 3: The Left Side of the Lower Receiver, Showing the Bolt Catch Above the Magazine Catch ______________ 4

Figure 4: Trigger with the Trigger Spring in Place _____________________________________________________ 4

Figure 5: the Trigger Pin Being Pushed Through The Trigger, Disconnector and Receiver ______________________ 4

Figure 6: Trigger and Disconnector Set Into the Lower Receiver __________________________________________ 4

Figure 7: The Hammer with Hammer Spring in Place __________________________________________________ 5

Figure 8:The Hammer Pinned in Position ____________________________________________________________ 5

Figure 9: The Trigger Guard ______________________________________________________________________ 5

Figure 10: Bottom of the Lower Receiver, Showing the Hole Where the Safety Selector Detent is Placed _________ 6

Figure 11: Safety Selector ________________________________________________________________________ 6

Figure 12: The Grip Screw ________________________________________________________________________ 6

Figure 13: The Grip Going Onto the Receiver with the Safety Selector Detent Spring Entering the Grip ___________ 6

Figure 14: The Takedown Pin (Near) and the Pivot Pin (Far) in Their Extended Positions ______________________ 7

Figure 15: Stock Receiver Plate ____________________________________________________________________ 7

Figure 16: Buffer Tube Holding the Buffer Stop in Position ______________________________________________ 7

Figure 17: Buffer Held in Position by the Buffer Stop ___________________________________________________ 8

Figure 18: Inserting the Buffer Spring and Buffer Into the Buffer Tube _____________________________________ 8

Figure 19: The Barrel Set Into the Upper Receiver ____________________________________________________ 11

Figure 20: The Barrel Nut Threaded Onto the Upper Receiver __________________________________________ 11

Figure 21: Gas Tube Inserted Through Barrel Nut and Into the Upper Receiver _____________________________ 11

Figure 22: The Charging Handle __________________________________________________________________ 12

Figure 23: Bolt Carrier Group ____________________________________________________________________ 12

Figure 24: Free Float Handguard _________________________________________________________________ 12

Figure 25: Handguard Lock Nut Tightened Against the Free Float Handguard _____________________________ 12

Figure 26: Gas Block with Gas Tube Inserted ________________________________________________________ 13

Figure 27: Gas Block Secured Onto the Barrel _______________________________________________________ 13

Figure 28: Flash Hider Fastened to the Barrel _______________________________________________________ 13

Figure 29: Completed Rifle With Its Accessories _____________________________________________________ 18

Overview ix

Overview

The instructions in this manual will guide you step-by-step through the process of

assembling a common AR-15 rifle. It assumes the rifle will use a free-float tube handguard,

as opposed to a traditional A2 handguard, and an adjustable carbine stock, as opposed to a

solid A2 stock. These decisions were made to reflect the increasing prevalence of these two

component types in custom civilian rifles. In all other respects, the instructions in this

manual are universal to the AR-15 platform and will be the same across all rifles.

Tools You Will Need

You will need several tools to assemble your AR-15. These tools include the following:

• 1 x Armorer’s Wrench with fittings for a carbine/M4 stock and flash hider

• 1 x Free-float tube wrench with fittings for a free-float barrel nut and locking nut

• 1 x Set of AR-15 pin punches

• 1 x Small, light hammer

• 1 x Small pliers

• 1 x Allen wrench set

With the above tools you will be able to completely assemble your rifle. However, there are

several items which you can invest in which will make working on your AR-15 much faster

and easier. They include:

• 1 x Vise and AR-15 action block

• 1 x A2 front sight bench block

Assembling the Lower

Assembling the Lower 3

Figure 1: The Pivot Pin in Extended Position

Figure 2: The Left Side of the Lower Receiver, Showing the

Magazine Catch

This section provides instructions on how to assemble the lower portion of the AR-15. This is commonly

referred to simply as the lower. The lower contains the majority of the moving parts and is the most

complex assemblies. It contains the lower receiver, which is for the purpose of firearms transfers

considered the weapon. All other pieces of the weapon may be bought and sold without restrictions. To

complete this assembly, you must complete the following steps:

1. Installing the pivot pin

2. Installing the magazine catch

3. Installing the bolt catch

4. Installing the trigger

5. Installing the hammer

6. Installing the trigger guard

7. Installing the safety selector

8. Installing the grip

9. Installing the takedown pin

10. Installing the stock and buffer tube

Installing the Pivot Pin

1. Insert the pivot pin detent spring into the hole running

along the right side of the lower receiver above the

magazine port.

2. Insert pivot pin detent on top of the pivot pin detent

spring.

3. Press the detent into the hole using the pivot pin while

inserting the front pivot pin through the front

brackets.

Installing the Magazine Catch

1. Insert magazine catch into the left side of lower

receiver.

2. Insert magazine catch spring into right side of

lower receiver around magazine catch.

3. Thread magazine catch button onto the

magazine catch post from the right side of the

lower receiver until the button is flush with the

magazine catch post.

4 Assembling an AR-15

Figure 3: The Left Side of the Lower Receiver, Showing

the Bolt Catch Above the Magazine Catch

Figure 4: Trigger with the Trigger

Spring in Place

Figure 6: Trigger and Disconnector Set Into the Lower Receiver

Figure 5: the Trigger Pin Being Pushed Through The Trigger,

Disconnector and Receiver

Installing the Bolt Catch

1. Tap the bolt catch roll pin into the right side of the bolt

catch mount, stopping before the pin emerges from the

first bracket.

2. Insert bolt catch spring.

3. insert bolt catch buffer.

4. Place bolt catch.

5. While holding the bolt catch in position, tap the bolt catch

roll pin through the bolt catch until it is flush.

Installing the Trigger

1. Wrap the trigger spring around the trigger.

2. Insert the disconnector spring into the top of the trigger.

3. Place trigger/spring assembly into lower receiver.

4. Set disconnector into trigger.

5. While holding the trigger and disconnector in place, insert the trigger pin

through the receiver, the trigger, and the disconnector until the trigger

pin is flush with both sides of the lower receiver.


Figure 7: The Hammer with

Hammer Spring in Place

Figure 8:The Hammer Pinned in Position

Figure 9: The Trigger Guard

Installing the Hammer

1. Wrap the hammer spring around the hammer.

2. Insert the hammer/spring assembly into the lower receiver so that the ends of

the spring rest upon the trigger pin.

3. While holding the hammer/spring assembly in position, insert the hammer

pin through the lower receiver and the hammer until the pin is flush on both

sides of the lower receiver.

Installing the Trigger Guard

1. Insert the end of the trigger guard with the

single pin into the brackets at the back of the

magazine port.

2. Line the opposite end of the trigger guard up

with the two holes behind the trigger.

3. Hold the trigger guard in position and tap the

trigger guard roll pin through the trigger

brackets behind the trigger until flush.


NOTE: The detent and spring will not

be secured until the pistol grip is

installed.

Figure 11: Safety Selector

Figure 10: Bottom of the Lower Receiver, Showing the Hole Where the Safety

Selector Detent is Placed

Figure 12: The Grip

Screw

Figure 13: The Grip Going Onto the Receiver with the Safety Selector Detent

Spring Entering the Grip

Installing the Safety Selector

1. Cock the hammer.

2. Insert the safety selector through the left side of the

lower receiver.

3. Place the safety selector detent into the hole below

the safety selector on the right side of the lower

receiver.

4. Place the safety selector detent spring into the same hole.

Installing the Grip

1. Place the grip onto the rear of the receiver, making certain that the safety selector

detent spring enters the hole at the top of the grip.

2. Using an allen wrench, drive the grip screw through the bottom of the grip into the

lower receiver until tight.


NOTE: The detent, spring, and pin

will not be secured until the buffer

tube has been installed.

Figure 14: The Takedown Pin (Near) and the Pivot Pin (Far) in

Their Extended Positions

Figure 15: Stock Receiver Plate

Figure 16: Buffer Tube Holding the Buffer Stop in

Position

Installing the Takedown Pin

1. Insert the takedown pin into the right side of the lower receiver.

2. Place the takedown pin detent into the hole at the rear of the lower receiver.

3. Insert the takedown pin spring into the hole at the rear of the lower receiver.

Installing the Stock and Buffer Tube

1. Make certain the stock receiver plate is around the end of the buffer tube,

and that it will mate correctly with the receiver.

2. Begin threading the buffer tube into the lower receiver, stopping before

you reach the buffer stop hole.

3. Insert the buffer stop spring into the buffer stop hole.

4. Insert the buffer stop.

5. Continue threading the buffer tube forward while holding down the buffer

stop until the buffer tube holds the buffer stop down but does not prevent

it from being depressed.

6. Tighten the buffer tube castle nut using a carbine stock castle nut wrench.


Figure 18: Inserting the Buffer Spring and Buffer Into the Buffer Tube

Figure 17: Buffer Held in Position by

the Buffer Stop

Installing the Buffer

1. Insert the buffer spring into the buffer tube.

2. While depressing the buffer stop, insert the buffer into the buffer tube.

Assembling the Upper 3

Assembling the Upper


Figure 19: The Barrel Set Into the Upper Receiver

Figure 20: The Barrel Nut Threaded Onto the Upper

Receiver

Figure 21: Gas Tube Inserted Through Barrel Nut and Into

the Upper Receiver

The upper portion of the weapon, generally referred to as simply the upper, contains the barrel and the

bolt carrier group, along with the upper receiver. It is the final portion of the rifle you will need to

assemble. You will need to complete the following steps:

1. Attaching the Barrel

2. Inserting the Bolt Carrier Group and Charging Handle

3. Installing the Free-Float Handguard

4. Pin and Secure the Gas Block

5. Installing the Flash Hider

Attaching the Barrel

1. Make certain any gas block the barrel may have is

removed.

2. Set the barrel into the upper receiver making certain

the pin on the barrel sits in the slot on the upper

receiver.

3. Thread the free float handguard barrel nut onto the

upper receiver and tighten using a free float

handguard barrel nut wrench.

4. Check to make sure the gas tube inserts easily and

parallel with the barrel through the barrel nut.

Adjust the barrel nut as necessary.


Figure 22: The

Charging Handle

Figure 24: Free Float Handguard

Figure 25: Handguard Lock Nut Tightened Against the Free Float

Handguard

Inserting the Bolt Carrier Group and Charging Handle

1. Slide the charging handle into the back of the upper receiver and up into the

charging handle track.

2. With the charging handle half-way extended, set the bolt carrier key into the track on

the bottom of the charging handle.

3. Move the bolt carrier group and charging handle forward until the bolt carrier group

locks into the breach of the barrel, and the charging handle clasps the upper receiver.

Installing the Free Float Handguard

1. Thread the free float handguard lock nut to the back

of the barrel nut.

2. Insert the gas tube through the barrel nut into the

upper receiver.

3. Thread the free float handguard onto the barrel nut as

far as you can while stopping at a position which

keeps any railing the handguard may have parallel

with the top of the upper receiver.

4. Using a free float handguard wrench, tighten the lock nut up against the free float tube.

Figure 23: Bolt Carrier Group


Figure 26: Gas Block with Gas Tube

Inserted

Figure 27: Gas Block Secured Onto the Barrel

Figure 28: Flash Hider Fastened to the Barrel

Pinning and Securing the Gas Block

1. Slide the gas block onto the barrel until the gas tube inserts

into gas block.

2. Align the gas tube and gas block so that you can see light

through the gas block pin hole.

3. While holding the gas tube in position, tap the gas block roll

pin through the gas block and gas tube until flush.

4. Slide the gas block and attached gas tube as far back on the

barrel as they will easily travel.

5. Tighten the gas block bolts using an allen wrench.

Installing the Flash Hider

1. Set the crush washer around the threaded end of the barrel.

2. Thread the flash hider onto the end of the barrel until it reaches the crush washer. No need to

tighten at this point.

3. Grasp the flash hider using your armorer’s wrench and tighten the flash hider, stopping when the

flash hider is properly oriented with its gas exits facing upward.

Completing Assembly and Operation Check

Completing Assembly and Operation Check 17

Finally, you’ll need to do some cleanup and testing with your AR-15. This section provides instructions

for lubricating and testing.

Lubricating Your Rifle

Now that the two halves of your rifle are fully assembled they need to be lubricated. You

may select any standard gun oil for this purpose.

1. Apply a drop of gun oil to the tracks of both the pivot and takedown pins. Cycle

the pins between their open and closed locked positions several times.

2. Apply a drop of gun oil to the hammer and trigger pins. Apply a drop of gun oil to

the back of the disconnector near the disconnector spring. Now cock the hammer

with your thumb and release it with the trigger while maintaining control of the

hammer with your thumb so it doesn’t snap forward and strike the receiver.

Repeat this several times.

3. Apply a drop of gun oil to the interior shaft of the fire selector. Cock the hammer.

Cycle the fire selector between fire and safe several times. Set the fire selector to

safe and pull the trigger while securing the hammer with your thumb. The

hammer should not release. Set the fire selector to fire and gently release the

hammer.

4. Place several drops of gun oil around the buffer at the top of the buffer tube.

Depress the buffer into the buffer tube several times.

5. Remove the bolt carrier group from the upper receiver. Apply a drop of gun oil to

the bolt cam below the carrier key. Apply a drop of gun oil around the base of the

bolt. Cycle the bolt back and forth in the bolt carrier group several times.

6. Place a drop of gun oil into the carrier key.

7. Place a drop of gun oil into each of the holes on the right side of the bolt carrier

group.

8. Return the bolt carrier group to the upper receiver. Apply a couple drops of gun

oil to the breach of the barrel and the sides of the bolt carrier group. Cycle the

bolt carrier group into and out of the barrel’s breach several times.

Complete Assembly and Operation Check

You are now ready to combine the two halves of your rifle and check to make sure

everything is functioning correctly. With the pivot and takedown pins in the open position,

set the upper into the lower. Press the pivot and takedown pins into their locked positions.

Your rifle should now be solidly connected.

Begin the operation check by grabbing the charging handle with the index and middle

fingers of your left hand. Pull the charging handle fully back and release it, just like a pinball

machine. The bolt carrier group should slide fully into the breach of the barrel. Repeat this

18

action several times to ensure the bolt carrier group is not catching.

Now set the fire selector to safe and pull the trigger. The hammer should not fall. Set the fire

selector to fire and pull the trigger. The hammer should fall and de

release the charging handle several times, changing the fire selector intermittently, until

you are confident the bolt carrier

hammer from falling, and the trigger releases

the safety.

WARNING

Before you begin the operation check you must make certain that there is no

ammunition in either the breach of the rifle or the magazine you will be using to

test.

Figure

Assembling an AR

action several times to ensure the bolt carrier group is not catching.


selector to fire and pull the trigger. The hammer should fall and de-cock the rifle. Pull and

several times, changing the fire selector intermittently, until

you are confident the bolt carrier group slides easily into the breach, the safety prevents the

hammer from falling, and the trigger releases the hammer smoothly when not stopped by


mmunition in either the breach of the rifle or the magazine you will be using to

Figure 29: Completed Rifle With Its Accessories

Assembling an AR-15


ck the rifle. Pull and

several times, changing the fire selector intermittently, until

group slides easily into the breach, the safety prevents the

the hammer smoothly when not stopped by


mmunition in either the breach of the rifle or the magazine you will be using to

Index 19

Index

barrel, 11

bolt carrier, 11, 12, 17, 18

bolt carrier group, v, vii, 11, 12

bolt catch, 4

bolt catch buffer, 4

bolt catch mount, 4

bolt catch roll pin, 4

bolt catch spring, 4

buffer, 8

buffer stop, 7, 8

buffer stop hole, 7

buffer tube, 7, 8

charging handle, v, vii, 11, 12, 17, 18

charging handle track, 12

crush washer, 13

disconnector spring, 4, 17

flash hider, v, vii, ix, 11, 13

free float handguard, 11, 12

free float tube, 12

gas block, 11, 13

gas tube, 11, 12, 13

grip, 6

gun oil, 17

hammer, 5, 6

hammer pin, 5

hammer spring, 5

handguard, 12

lower receiver, 3, 4, 5, 6, 7

lubricating, 17

magazine catch, 3

magazine catch button, 3

magazine catch post, 3

magazine catch spring, 3

magazine port, 3, 5

pistol grip, 6

pivot pin, 3

pivot pin detent, 3

pivot pin detent spring, 3

roll pin, 5

safety selector, 6

safety selector detent spring, 6

stock, 7

stock receiver plate, 7

takedown pin, 7

takedown pin detent, 7

takedown pin spring, 7

the upper, 11

trigger, 4

trigger guard, 5

trigger pin, 5

trigger spring, 4

upper receiver, 11, 12, 17

Documents

How To Assemble an AR-15