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Work order — AR-15 (M16/M4 Pattern)

Taking the firearm apart for a job such as refinishing, and putting it back together to specification. Generated from the Pew-Takedown entry last updated 2026-10-29. Confidence: high.

Shop difficulty: Tier 2 of 3

About 72 key numbers, and the bolt is broken out. It all comes apart with punches and a couple of AR wrenches. The known traps are the spring-loaded pivot and takedown detents, the roll pins that mar the receiver, the ejection port cover spring that has to be pre-wound, and the hammer spring orientation. Barrel removal needs vise blocks and a torque wrench. 92 parts (complete rifle, M16A1 configuration (with forward assist), magazine included, per the TM 9-1005-249-23&P Repair Parts List figs. C-1 to C-14; semi-auto parts only: the automatic sear assembly (fig. C-). Pew-Takedown's rating, not the manufacturer's.

Bench time: strip ~40 min, rebuild ~60 min (estimate). Actual: strip ______ rebuild ______

Special tools:

• Upper receiver vise block / reaction rod — Holding the upper for barrel nut and muzzle device work
• AR armorer's wrench (barrel nut/castle nut) — Barrel nut and receiver extension castle nut
• Torque wrench (ft-lb and in-lb) — Barrel nut, castle nut, muzzle device
• Pivot pin detent installation tool (or 3/32" punch) — Holding the pivot pin detent while the pin goes in
• Roll-pin starter punches (1/16", 3/32", 1/8") and a bench block — Bolt catch, trigger guard, forward assist and ejection port cover pins
• Lower receiver vise block — Supporting the trigger guard ears and bolt catch boss

Watch for:

• The front pivot pin and rear takedown pin each sit on a spring-loaded detent that launches when the pin comes out; reinstalling the pivot pin means holding the detent down while the pin goes in, which is the classic AR lower trap. (both; Shooting Illustrated (NRA))
• The TM has the armorer use a pivot pin tool to compress the detent, and warns to catch the detent and spring as the pin comes out. (both; Department of the Army)
• The bolt catch and trigger guard roll pins mar the receiver unless the receiver is taped and supported and a roll-pin starter punch is used. (both; The Firearm Blog)
• The ejection port cover spring has to be pre-wound half a turn and held while its pin goes in. (reassembly; Department of the Army)
• The hammer spring legs must ride on the trigger pin and the hammer has to be held down to line up the hammer pin; reversed, the hammer is weak. (reassembly; The Firearm Blog)

Tools

• Punch or a cartridge rim — Pushing out stubborn takedown pins on a tight rifle.
• Small punch or paperclip — Removing the firing pin retaining pin from the bolt carrier group.

1. Clear and make safe

1. Point the muzzle in a safe direction and keep your finger off the trigger.
2. Press the magazine release and remove the magazine.
3. Pull the charging handle fully to the rear and lock the bolt back using the bolt catch.
4. Visually inspect the chamber and the magazine well, then physically feel the chamber to confirm it is empty.
   Warning: Check both the chamber and the magazine well. A round can be hung up in the well.
5. If the hammer is cocked, place the selector on SAFE. If the selector will not move to SAFE, the hammer is down — leave the selector alone and continue with the muzzle in a safe direction.
   Tip: Once the upper and lower are separated, selector position no longer matters for disassembly.
6. Remove all live ammunition from the work area.

2. Disassemble

Field Strip

1. Complete the Clear and Make Safe procedure and release the bolt forward.
2. Push the rear takedown pin from the left side of the lower receiver until it stops in its captured position.
   Tip: If it is tight, tap it with a punch or the rim of an empty case rather than levering it.
3. Pivot the upper receiver forward and away from the lower on the front pivot pin.
4. Push the front pivot pin out from the left side to its captured position, then separate the upper receiver from the lower receiver.
   Tip: You can stop here for most cleaning. Separating the receivers is optional if you only want to reach the bolt.
5. Pull the charging handle partway to the rear. The bolt carrier group will follow it out of the upper receiver — grasp the carrier and withdraw it.
6. With the carrier out, pull the charging handle down and out of its channel in the upper receiver.
   Warning: The charging handle must come out after the carrier, not before. It will not clear its channel otherwise.

Disassemble the Bolt Carrier Group

1. Remove the firing pin retaining pin (a small cotter pin) from the side of the carrier using a punch or your fingers.
   Tip: It only needs to come out far enough to clear the firing pin — do not fully remove and lose it.
2. Tip the carrier back and let the firing pin drop out of the rear.
   Warning: Do not pry the firing pin out. If it will not drop, the bolt is not pushed forward.
3. Push the bolt forward into the carrier, rotate the cam pin 90 degrees, and lift it straight out.
   Warning: The cam pin is the single most important part not to lose. A rifle assembled without it is dangerous.
4. Pull the bolt straight out of the front of the carrier.
5. To remove the extractor, push out the extractor pin with a small punch and lift the extractor and its spring assembly off the bolt.
   Warning: The extractor spring has a rubber or polymer insert that must not be removed or lost — it provides part of the extractor tension.
6. Clean the bolt tail, the carrier's interior, the gas rings, and the bolt lugs. Inspect the gas rings — their gaps should not all line up, and the bolt should hold its own weight when the carrier is stood on the bolt face.

Remove the Buffer and Buffer Spring

1. Separate the upper from the lower receiver and verify the rifle is unloaded.
2. Press the buffer retainer — the small pin at the front of the receiver extension — down with a fingertip while holding the buffer with your other hand.
   Warning: The buffer is under spring pressure and will launch forward. Keep a hand on it and wear eye protection.
   Tip: Make sure the hammer is cocked before you remove or install the buffer (TM 9-1005-319-23&P).
3. Ease the buffer and buffer spring forward and out of the receiver extension.

Remove the pistol grip, buttstock, takedown pin and pivot pin

1. Separate the upper receiver from the lower receiver (entry's field strip).
2. Remove the pistol grip screw and lockwasher.
3. Carefully remove the pistol grip and catch the helical spring and safety detent.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
4. Fixed rifle stock: remove the self-locking buttstock screw.
   Warning: If the self-locking screw is removed, it must be discarded and replaced with a new one.
5. Fixed rifle stock: remove the buttstock assembly carefully and catch the helical spring, takedown pin detent, takedown pin and stepped spacer.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
   Tip: If the detent will not come out, use a wire to push it out.
6. Collapsible carbine stock: extend the buttstock, grasp the lock release lever near its retaining nut, pull it downward and slide the buttstock to the rear off the lower receiver extension.
7. Depress the pivot pin detent and spring and remove the pivot pin, or insert the fabricated pivot pin removal tool to compress the detent, turn the pivot pin a quarter turn, then remove the tool and the pivot pin.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
8. Hold a cupped hand in front of the pivot pin detent and helical spring as the pin comes out, to catch them.
   Tip: If the helical spring will not come out, use a wire to pull it out.

Remove the bolt catch, magazine catch, selector, hammer and trigger

1. Remove the pistol grip and buttstock (procedure 'lower-receiver-grip-stock-pins-removal').
2. Remove the bolt catch spring pin with a 3/32-inch drive pin punch and hammer.
3. Remove the bolt catch, bolt catch plunger and bolt catch spring.
4. Press in on the magazine button with a drive pin punch and turn the magazine catch counterclockwise to unscrew and remove it.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
5. Remove the magazine button and magazine catch spring.
6. Remove the safety selector lever.
   Tip: At this point the military rifle has an additional part that the semiautomatic AR-15 does not have; it is not covered here.
7. With the hammer forward, push the hammer pin out of the lower receiver with a drive pin punch.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
   Tip: If the selector lever is still installed, the TM places it on SEMI for this step.
8. Remove the hammer assembly.
9. Push the trigger pin out from the left side of the lower receiver with a drive pin punch.
10. Remove the disconnector and trigger assembly from the lower receiver.

Remove the hammer and trigger springs

1. Remove the hammer spring from the hammer.
2. Remove the disconnector spring and trigger spring from the trigger.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.

Remove the trigger guard and lower receiver extension

1. Remove the buffer and action spring (entry's 'buffer-removal') and the buttstock (procedure 'lower-receiver-grip-stock-pins-removal').
2. Remove the trigger guard spring pin with a 1/8-inch drive pin punch and hand hammer.
3. Remove the trigger guard.
4. Fixed rifle stock: put padding between the lower receiver and brass vise jaws that conform to it, and clamp the solid portion of the lower receiver just tight enough to hold.
5. Fixed rifle stock: unscrew the lower receiver extension with the combination wrench and socket wrench handle, catching the buffer retainer and helical spring.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
6. Carbine: clamp the solid portion of the lower receiver in a vise with wooden jaws, just tight enough to hold.
7. Carbine: loosen the extension locking nut with the special tool.
8. Carbine: loosen the locking nut far enough for the receiver end plate to disengage from the lower receiver, hold the buffer retainer and spring in place with your index finger, and unscrew the lower receiver extension.
   Warning: Restrain the pivot pin spring and detent while doing this (TM caution).

Remove the handguards, front sight post, sling swivel and ejection port cover

1. Separate the upper receiver and barrel assembly from the lower receiver.
2. Push down on the handguard slip ring and lift the upper handguard assembly up and out.
   Warning: Do not use a screwdriver or any other tool when removing the handguard assemblies — it may damage them or the slip ring. Do not remove the heat shield for any reason.
   Tip: The operator's manual describes a 'buddy system' for this.
3. Push down on the handguard slip ring and lift the lower handguard assembly up and out.
4. Only if damaged: remove the front sight post by turning it counterclockwise with a dummy cartridge or the front sight post removal and installation tool.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
5. Catch the front sight detent and helical spring.
6. Rifle, only if repair is necessary: knock out the tubular rivet with a hammer and punch, remove the small sling swivel and discard the rivet.
7. Carbine, only if repair is necessary: remove the two spring pins, lift the swivel locking bar up and out of the swivel mount, remove the swivel mount, then remove the rivet and separate the front swivel from the mount.
8. Only if repair is necessary: remove the retaining ring and slide the headless grooved pin out to the rear.
   Tip: The pin may bind against the forward assist housing and need some extra force.
9. Catch the cover spring and ejection port cover as the pin comes out.

Remove the gas tube, compensator and barrel

1. Remove the handguards (procedure 'upper-receiver-unit-detail-strip') and separate the upper from the lower receiver.
2. Drive the spring pin that retains the gas tube out of the front sight assembly with a ball-peen hammer and 5/64-inch drive pin punch.
3. Slide the gas tube back into the upper receiver to clear the front sight assembly, then lift it slightly, pull it forward and remove it.
4. Position the upper receiver and barrel assembly in the barrel removal fixture and secure both in a machinist's vise.
5. Remove the compensator with the combination wrench and a 12-inch drive handle.
6. Remove the peel washer without losing or bending its thin sections.
7. Take the assembly out of the fixture and vise, then place it in the barrel removal fixture again and clamp it in the vise for barrel nut removal.
8. With all three drive pins of the combination wrench engaged in the barrel nut and the wrench pushed toward the upper receiver to compress the slip ring spring, loosen the barrel nut assembly with the drive handle.
   Warning: Do not use a torque wrench to loosen the barrel nut assembly.
9. Separate the upper receiver assembly from the barrel assembly.
10. Remove the barrel assembly from the vise and barrel removal fixture.
11. Remove the retaining ring with retaining ring pliers.
12. Remove the slip ring spring and handguard slip ring.
    Warning: Do not remove the barrel nut from the barrel assembly.

Remove the A2 rear sight and the forward assist

1. Drive out the windage knob spring pin with a hammer and 1/16-inch punch.
   Warning: Be sure to catch the small parts.
2. Catch the rear sight windage knob, helical spring and ball bearing.
3. Remove the rear sight windage screw with a flat-bladed screwdriver.
4. Remove the sight aperture and flat spring from the upper receiver.
5. Drive out the elevation spring pin with a 3/32-inch punch and catch the helical spring as the punch is withdrawn.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
6. Rotate the elevation index until the rear sight base clears the upper receiver, catching the ball bearing and helical spring as it clears.
7. Push the elevation index out with your thumb using a slight rotating motion, and catch the ball bearing and helical spring.
8. Remove the index screw with a 1/16-inch Allen wrench, discard it, and separate the elevation index from the elevation knob by hand.
9. Remove the forward assist spring pin with a 3/32-inch drive pin punch and hand hammer.
10. Remove the forward assist assembly and its helical spring from the upper receiver.
    Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.

Disassemble the forward assist

1. Drive out the spring pin with a 1/16-inch drive pin punch and hand hammer.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
2. Remove the forward assist pawl, pawl detent and helical spring from the plunger assembly.

3. Refinish

The components the procedures above separate. Coating, masking and cure are outside this database; follow your coating system's instructions. A part the manufacturer marks "factory fit" should not be swapped or reworked.

No manufacturer statement of materials or finish is recorded. Identify each part's material before choosing prep and cure.

4. Reassemble

Disassemble the forward assist

1. Reverse the steps of "Disassemble the forward assist".

Remove the A2 rear sight and the forward assist

1. Reverse the steps of "Remove the A2 rear sight and the forward assist".

Remove the gas tube, compensator and barrel

1. Reverse the steps of "Remove the gas tube, compensator and barrel".

Remove the handguards, front sight post, sling swivel and ejection port cover

1. Reverse the steps of "Remove the handguards, front sight post, sling swivel and ejection port cover".

Remove the trigger guard and lower receiver extension

1. Reverse the steps of "Remove the trigger guard and lower receiver extension".

Remove the hammer and trigger springs

1. Reverse the steps of "Remove the hammer and trigger springs".

Remove the bolt catch, magazine catch, selector, hammer and trigger

1. Reverse the steps of "Remove the bolt catch, magazine catch, selector, hammer and trigger".

Remove the pistol grip, buttstock, takedown pin and pivot pin

1. Reverse the steps of "Remove the pistol grip, buttstock, takedown pin and pivot pin".

Remove the Buffer and Buffer Spring

1. To reinstall, insert the spring and buffer, compress until the buffer nose clears the retainer, and let the retainer snap up in front of it.
   Warning: Confirm the buffer retainer has popped back up and is holding the buffer. If it has not, the buffer will come out when the upper is removed and the spring can launch.

Disassemble the Bolt Carrier Group

1. Reverse the steps of "Disassemble the Bolt Carrier Group".

Install the pivot pin, takedown pin, buttstock and pistol grip

1. Install the fabricated pivot pin installation tool, insert the helical spring and pivot pin detent, compress the detent into its recess with a 3/32-inch punch and rotate the tool, then remove the punch.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
2. Install the pivot pin while removing the installation tool, keeping pressure on the pin as it slides into the hole, and rotate the pivot pin until the detent enters its groove.
   Tip: The rounded end of the pivot pin detent must be in the groove of the pivot pin when assembly is complete.
3. Fixed rifle stock: install the takedown pin with its groove toward the rear, then install the takedown pin detent and helical spring from the rear.
   Warning: Do not kink the helical spring during assembly.
4. Fixed rifle stock: install the stepped spacer on the receiver extension and carefully slide the buttstock assembly on to compress the helical spring.
5. Fixed rifle stock: secure the buttstock assembly with a new self-locking screw.
6. Collapsible carbine stock: grasp the lock release lever near the retaining nut, pull, and slide the buttstock assembly onto the lower receiver extension.
7. Install the safety detent, pointed end first, and its helical spring into the bottom of the lower receiver.
   Warning: Do not kink the helical spring during assembly.
8. Carefully install the pistol grip so that it compresses the helical spring, and secure it with the lockwasher and screw.
   Warning: With the enhanced rifle grip (PN 9349127), the TM authorizes only a 1-1/8 in. or 1 in. grip screw; any screw longer than 1-1/8 in. could cause a hazardous situation. Make sure the washer is in place.
   Tip: Part of the helical spring fits into a hole in the pistol grip.

Install the trigger, hammer, selector, magazine catch and bolt catch

1. Install the trigger assembly and disconnector into the lower receiver.
2. Install the trigger pin with a drive pin punch, pushing it in until flush.
3. Install the hammer assembly with the ends of the hammer spring to the rear of the trigger pin, resting in the annular groove on the upper surface of the trigger pin.
4. Install the hammer pin with a drive pin punch, pushing it in until flush.
5. Install the safety selector lever.
   Tip: TM 9-1005-319-23&P (p. 3-71): the hammer should be cocked before the selector lever is installed. At this point the military rifle has an additional part that the semiautomatic AR-15 does not have; it is not covered here.
6. Install the magazine catch spring and magazine button.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
7. Push in on the magazine button with a drive pin punch and turn the magazine catch clockwise until its threaded end is flush with the magazine button head.
   Tip: TM 9-1005-319-23&P: the punch should be larger than the hole in the magazine button.
8. Install the bolt catch spring, bolt catch plunger and bolt catch.
9. Secure the bolt catch by installing the spring pin with a 3/32-inch drive pin punch and hand hammer.
10. Install the pistol grip and buttstock (procedure 'lower-receiver-grip-stock-pins-installation'), then function check the rifle.
    Tip: TM 9-1005-249-23&P para 3-20: with the selector on semi, the hammer must not fall with 5.5 lb on the trigger and must fall by 8.5 lb.

Install the hammer and trigger springs

1. Install the hammer spring on the hammer.
2. Install the disconnector spring by inserting the large end of the spring into the trigger.
3. Install the trigger spring on the trigger.

Install the lower receiver extension and trigger guard

1. Fixed rifle stock: install the helical spring and buffer retainer into the lower receiver.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
2. Fixed rifle stock: lubricate the threads of the lower receiver and lower receiver extension with molybdenum disulfide grease.
3. Fixed rifle stock: install the lower receiver extension into the lower receiver while depressing the buffer retainer.
4. Fixed rifle stock: clamp the solid portion of the lower receiver in padded, conforming vise jaws and torque the extension with the combination wrench and torque wrench, reading torque with both wrenches used together.
5. Carbine: lubricate the threads of the lower receiver and extension with molybdenum disulfide grease.
6. Carbine: pre-position the spring and buffer retainer in the lower receiver, and screw the locking nut onto the extension with its three notches facing forward.
7. Carbine: fit the receiver end plate onto the extension with its lug facing forward.
8. Carbine: pre-position the takedown pin, detent and spring in the lower receiver.
9. Carbine: push down on the buffer retainer and spring and screw the extension in until it retains the buffer retainer.
10. Carbine: align the end plate lug into the rear of the lower receiver and screw the locking nut forward until it contacts the end plate.
11. Carbine: tighten the locking nut snug with the special tool, then torque it with the special tool and a torque wrench.
12. Carbine: stake the receiver end plate in two places across from the notches in the locking nut.
13. Install the trigger guard into the lower receiver.
14. Install the trigger guard spring pin with a 1/8-inch drive pin punch and hand hammer.

Install the ejection port cover, sling swivel, front sight post and handguards

1. Position the ejection port cover and helical spring on the upper receiver, with the short leg of the spring to the rear on the inside of the cover.
2. Hold the spring's short leg in place and turn the long leg one half turn (180 degrees) with your fingers.
3. Position the long leg against the ejection port cover, hold spring and cover in place, and install the headless grooved pin, checking spring tension as you install the retaining ring.
4. Rifle: position the small sling swivel and install a new tubular rivet, spreading and flaring its hollow head with a center punch and hammer.
5. Carbine: install the front swivel to the swivel mount with a new rivet, flaring it with a center punch and hammer; install the swivel mount, place the swivel locking bar in it and install the two spring pins.
   Tip: The TM recommends the mount on the left for right-handed shooters and on the right for left-handed shooters.
6. Position the helical spring and front sight detent in the front sight.
7. Install the front sight post by turning the removal and installation tool clockwise until the post's base is flush with or slightly below the front sight frame.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
8. Install the top of the upper handguard assembly in the tube cap while pushing down on the handguard slip ring, push the bottom of the handguard into place and release the slip ring.
9. Install the lower handguard assembly the same way, then release the slip ring to lock both handguards.

Install the barrel, compensator and gas tube

1. Slide the barrel nut to the rear of the barrel assembly as far as it will go.
2. Slide the handguard slip ring over the barrel nut.
3. Press the slip ring spring from both sides and insert it into the handguard slip ring.
4. Install the retaining ring against the slip ring spring with retaining ring pliers and snap it onto the barrel nut.
5. Apply molybdenum disulfide grease to the barrel nut threads.
6. Position the barrel assembly with its alignment pin up and clamp it in the vise using the barrel remover fixture.
   Tip: The alignment pin must not show any looseness.
7. Align the slot in the upper receiver with the barrel's alignment pin and install the upper receiver over the end of the barrel.
   Tip: The slot should fit the pin with very little or no rotational play.
8. Wipe the upper receiver threads clean, check for burrs, and apply molybdenum disulfide grease to them.
9. Engage the barrel nut threads with the upper receiver.
10. Torque the barrel nut with the combination wrench and torque wrench, then loosen it, torque it again, and loosen it again.
    Warning: Make certain all three drive pins of the combination wrench are engaged. Do not use the torque wrench for loosening.
11. With the front sight post installed, align the bore on a distant vertical target and check that the front sight post is on line and vertical with it; adjust rear sight windage for a proper sight picture.
    Tip: If excessive windage is needed, the barrel's alignment pin does not fit the receiver slot properly and the upper receiver must be replaced.
12. Torque the barrel nut a third time while maintaining sight alignment, tightening further only as needed to bring a serration in line for gas tube clearance.
    Warning: Never loosen the barrel nut to align it for gas tube clearance, and do not exceed the TM's maximum when tightening to the next hole.
13. Check barrel nut alignment by passing the front 8 inches of a gas tube (or a No. 15 drill) through the carrier key and the rear of the receiver; it must pass freely and lie top dead center along the barrel.
14. Install the peel washer, thin sections to the rear, and the compensator on the barrel.
15. Torque the compensator with the combination wrench and torque wrench so that part of the third (middle) slot opening is straight up in line with the front sight post, removing or adding peel washer sections as required.
16. Slide the gas tube through the barrel nut assembly and forward into the hole in the front sight assembly base, and align the holes in the gas tube and the base.
17. Drive the spring pin into the front sight assembly base with a ball-peen hammer and 5/64-inch drive pin punch to secure the gas tube.
18. Install the upper and lower handguard assemblies.
19. Check headspace with the headspace gage before returning the rifle to service.
    Warning: Headspace is checked with the TM's gage and procedure (para 3-10e). After rebarreling, the TM requires function firing and targeting the rifle.

Install the forward assist and the A2 rear sight

1. Apply CLP to the helical spring and forward assist assembly and install them in the upper receiver.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
2. Install the forward assist spring pin with a 3/32-inch drive pin punch and hand hammer.
3. Assemble the elevation knob and elevation index with a new index screw and a 1/16-inch Allen wrench.
   Warning: Do not overtighten the index screw; the scale will need adjustment.
4. Install the ball bearing and helical spring with needle nose pliers or tweezers.
5. Depress the ball bearing with a punch through the access hole and slide the elevation knob assembly into the upper receiver from the side, centering it.
6. Insert the threaded portion of the rear sight base into the upper receiver and rotate the elevation knob assembly until the threads engage.
   Tip: All three springs are identical when new; if their lengths now differ, use the longest in the windage knob and the shortest under the elevation knob ball.
7. Insert the helical spring and ball bearing in their hole as the rear sight base is lowered, rotate until the base is all the way down, then come up 22 clicks.
8. Insert the helical spring through the underside of the upper receiver, compress it with a small screwdriver and install the spring pin, then rotate the elevation knob until the rear sight base is all the way down.
   Warning: The spring pin must pass over the helical spring, not through its coils.
9. Install the flat spring and sight aperture in the rear sight base and install the windage screw with a screwdriver.
10. Insert the helical spring and ball bearing into the windage knob.
    Tip: Tilt the upper receiver toward the windage knob to keep from losing the ball bearing.
11. Position the windage knob on the windage screw shaft, align the holes with a small screwdriver or punch, and install the spring pin.
12. Rotate the elevation index and windage knob to check they work freely.
13. Check the elevation zero: with the sight bottomed on its last whole click, the 300 m mark must align with the mark on the receiver; if not, loosen the index screw three turns, rotate the lower knob counterclockwise to its stop, and retighten the index screw.

Reassemble the forward assist

1. Lubricate the helical spring, pawl detent and forward assist pawl with CLP.
2. Install the helical spring, pawl detent and forward assist pawl into the plunger assembly.
   Warning: To avoid injury to your eyes, use care when removing and installing spring-loaded parts.
3. Align the holes and install the spring pin with a 1/16-inch drive pin punch and hand hammer, flush or slightly below flush.

Reassembly

1. Insert the bolt into the carrier with the extractor on the same side as the ejection port when the carrier is oriented normally.
2. Push the bolt fully into the carrier, drop the cam pin into its hole, and rotate it 90 degrees so it lies across the carrier.
   Warning: If the cam pin is not rotated, the firing pin will not seat. Never force the firing pin.
3. Drop the firing pin into the rear of the carrier, tail first, and let it seat fully.
4. Install the firing pin retaining pin. If it will not go in, the cam pin is not installed or not rotated — stop and correct it.
   Warning: This is the design's built-in check. Do not defeat it.
5. Insert the charging handle into its channel in the upper receiver and push it partway forward, leaving it slightly open.
6. Insert the bolt carrier group into the charging handle's rear track, with the bolt extended forward, and slide both fully home.
7. Mate the upper receiver to the lower, press the front pivot pin home, close the receivers, and press the rear takedown pin home.
8. Charge the rifle and perform the function check.

5. Torque

Reported by other sources — not the manufacturer

Notes: From the US Army's unit and direct support maintenance manual for the M16 and M16A1, TM 9-1005-249-23&P — a primary source for the military rifle this pattern comes from, and armorer-level work. These values are for mil-spec pattern parts: the delta-ring barrel nut with gas-tube alignment, the M16/M16A1 flash suppressor, and the fixed rifle-stock receiver extension. Many commercial AR-15s use free-float handguards whose barrel nuts are proprietary and have their own values from the handguard maker, and carbine receiver extensions with a castle nut are not covered here. Use the values for the parts actually on the rifle. The TM also carries a generic torque table for unspecified fasteners (appendix F); it is not reproduced, because it is not specific to any part of this rifle.

Fit or check on rebuild

• Barrel nut torque and gas tube alignment — The barrel nut is torqued within a range and indexed for the gas tube
• Headspace if the barrel or bolt is changed — Bolt-to-barrel headspace is set by the factory; mixing bolts and barrels needs a gauge check
• Gas key staking and screw torque — If the carrier key is disturbed the screws are torqued and staked
• Function check (safety, hammer reset, disconnector) — The hammer spring orientation and disconnector seating are checked with a function check
• Sight/optic re-zero — The front sight base, rail or optic moves when the barrel/handguard comes off

6. Function check

• Verify the rifle is unloaded with no magazine inserted before each step.
• Charge the rifle to cock the hammer, then place the selector on SAFE and press the trigger. The hammer must not fall.
• Move the selector to SEMI and press the trigger. The hammer should fall.
• Hold the trigger to the rear, charge the rifle, then release the trigger slowly. You should hear and feel the disconnector release the hammer to the trigger — a distinct click.
• Press the trigger again. The hammer should fall.
• Push the forward assist and confirm the bolt goes fully into battery.
• Insert an empty magazine, charge the rifle, and confirm the bolt locks back on the empty magazine.

If any check fails, the firearm is not safe to fire. Stop and see a licensed gunsmith.

If it won't go back together

Sources

1. TM 9-1005-319-10: Rifle, 5.56mm, M16A2/M4 Carbine — U.S. Department of the Army primary
2. FM 3-22.9: Rifle Marksmanship M16-/M4-Series Weapons — U.S. Department of the Army primary
3. Colt AR-15 Owner's Manual — Colt's Manufacturing Company primary
4. TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1 — Headquarters, Department of the Army primary
   https://archive.org/details/ArmyTechnicalManualforM16Rifle-Tm9-1005-249-23p
5. TM 9-1005-319-23&P (Air Force TO 11W3-5-5-42), Unit and Direct Support Maintenance Manual incl. RPSTL: Rifle, 5.56 mm, M16A2; Carbine, 5.56 mm, M4/M4A1 (with Changes 1-5) — Headquarters, Department of the Army / Department of the Air Force primary
   https://archive.org/download/milmanual-tm-9-1005-319-23-m16a2-maintenance--repair-manual/tm_9-1005-319-23_m16a2_maintenance__repair_manual.pdf
6. ASAP (Ambidextrous Sling Attachment Point) Installation Instructions — Magpul Industries secondary
   https://magpul.com/media/wysiwyg/Instructions/MAG500_ASAP_INSRT.pdf
7. Installation Instructions — Geissele Super Modular Rail, MK8 Magpul M-LOK Rails — Geissele Automatics (document hosted by MidwayUSA) secondary
   https://media.midwayusa.com/productdocuments/instructions/618/installation_geissele_mk8.pdf
8. Free Float Hand Guard Installation Instructions — Midwest Industries, Inc. secondary
   https://midwestindustriesinc.com/content/installation-instructions/AR15-Free-Float-Handguard-Instructions.pdf
9. Installation Manual for BCM KMR Series Handguards (KMR-A, MCMR, QRF), Rev. 4/21 — Bravo Company MFG (BCM) secondary
   https://www.bravocompanymfg.com/downloads/kmr_installation_instructions.pdf
10. AR15 BAR Barrel Nut Installation — Aero Precision secondary
    https://www.aeroprecisionusa.com/media/downloadable/bar-barrel-nut-instructions.pdf
11. TM 9-1005-249-23&P Unit and Direct Support Maintenance Manual (Including Repair Parts and Special Tools List): Rifle, 5.56mm, M16 and M16A1 — Departments of the Army and Air Force; Commandant, Coast Guard primary
    https://archive.org/download/ArmyTechnicalManualforM16Rifle-Tm9-1005-249-23p/Manual-Tm9-1005-249-23p.pdf
12. ATLAS (Aero Taper Lock Attachment System) Installation Instructions — Aero Precision secondary
    https://www.aeroprecisionusa.com/media/downloadable/ATLAS-install-Instructions.pdf
13. Aero Precision Support Center — How to install a R-ONE/S-ONE Handguard (updated 2025-01-09; read via the help centre's Zendesk API) — Aero Precision secondary
    https://support.aeroprecisionusa.com/hc/en-us/articles/14130449931671-How-to-install-a-R-ONE-S-ONE-Handguard
14. MOD 4: 7 Sided M-LOK Handguard — Aero Precision product page — Aero Precision secondary
    https://www.aeroprecisionusa.com/mod-4-m-lok-handguard-pro-lineup
15. Aero Precision Support Center — How to build your M4E1 Lower Receiver (updated 2024-01-24; read via the help centre's Zendesk API) — Aero Precision secondary
    https://support.aeroprecisionusa.com/hc/en-us/articles/14130428430359-How-to-build-your-M4E1-Lower-Receiver
16. Aero Precision C.O.P. Kit Manual (Proof 6, 09/03/2013) — AR15 C.O.P. Kit Assembly Manual — Aero Precision secondary
    https://www.aeroprecisionusa.com/media/downloadable/Aero-Precision-COP-Kit-Manual.pdf
17. BCM MCMR-13 (M-LOK Compatible Modular Rail) — product page — Bravo Company MFG (BCM) secondary
    https://bravocompanyusa.com/bcm-mcmr-13-m-lok-compatible-modular-rail/
18. Midwest Industries — SP Series Installation Instructions (AR15) — Midwest Industries, Inc. secondary
    https://midwestindustriesinc.com/content/installation-instructions/AR15-SP-Series-Handguard-Instructions.pdf
19. Midwest Industries — Two Piece Extended Free Float M-Lok Handguard Installation Instructions (AR15) — Midwest Industries, Inc. secondary
    https://midwestindustriesinc.com/content/installation-instructions/AR15-Two-Piece-Extended-Free-Float-Handguard-M-LOK-Instructions.pdf
20. Daniel Defense MFR / MFR XL Rail (M-LOK) — Installation Instructions, Rev 1.0 (served from www.danieldefense.com; the bare danieldefense.com host returns 403) — Daniel Defense, Inc. secondary
    https://www.danieldefense.com/media/asset/m/f/mfr_mfrxl_rail_m-lok_instructions.pdf
21. Daniel Defense MFR XS Rail — Installation Instructions (served from www.danieldefense.com) — Daniel Defense, Inc. secondary
    https://www.danieldefense.com/media/asset/m/f/mfr_xs_rail_installation_instructions.pdf
22. Daniel Defense DDM4 Rail — Installation Instructions, Rev 1.0 (served from www.danieldefense.com) — Daniel Defense, Inc. secondary
    https://www.danieldefense.com/media/asset/d/d/ddm4_rail_instructions.pdf
23. Daniel Defense RIS II — Installation Instructions (served from www.danieldefense.com) — Daniel Defense, Inc. secondary
    https://www.danieldefense.com/media/asset/r/i/ris_ii_instructions.pdf
24. WORKHORSE 13" Free Float Rail M-LOK Rail Handguard w/ ASAL Lock — BATTLEARMS product page (same 'Installation Torque Recommendations' on the WORKHORSE 4" page) — Battle Arms Development, Inc. (BAD / BATTLEARMS) secondary
    https://battlearmsdevelopment.com/shop/bad-wh-hg-mlok-13-workhorse-13-free-float-rail-m-lok-rail-handguard-w-asal-lock-920
25. BATTLEARMS RIGIDRAIL Free Float Rail Handguards for the M16 . M4 . AR-15 or AR-10 Weapon Platforms — Instructions (maker's PDF re-hosted by distributor OpticsPlanet; no copy found on battlearmsdevelopment.com) — Battle Arms Development, Inc. (BAD / BATTLEARMS) secondary
    https://www.opticsplanet.com/i/pdf/opplanet-battle-arms-development-rigidrail-ar15-m16-free-float-rail-handguards-installation-pdf.pdf
26. ODIN Works O2 Lite M-LOK Forend (AR-15 > Upper > Forends) — product page, 'Forend Installation Instructions' (same text on the 7" and 9" pages) — ODIN Works secondary
    https://www.odinworks.com/O2-Lite-M-LOK-Forend-p/f-15-ml-o2.htm
27. ODIN Works 1 1/4" Jumbo Crowfoot Wrench (for ODIN Works 223/5.56 Forend installation) — product page — ODIN Works secondary
    https://www.odinworks.com/1-1-4-Jumbo-Crow-Foot-Wrench-p/acc-1-1-4-crowfoot-223.htm
28. ODIN Works Suppressor Mount (OSM) 5 — product page, 'OSM Installation' — ODIN Works secondary
    https://www.odinworks.com/ODIN-Suppressor-Mount-5-p/sup-osm-5.htm
29. Faxon 15" G3 Streamline Aluminum M-LOK AR15 Handguard — product page 'Installation Instructions' (same text on the 6/7/9/13/17" G3 pages) — Faxon Firearms secondary
    https://faxonfirearms.com/FFHGMLOK15G415
30. Faxon MuzzLok Gunner 3-Port 5.56 Muzzle Brake – Nitride | 1/2x28 — product page — Faxon Firearms secondary
    https://faxonfirearms.com/FFMD5563PMBSQPQ
31. KAK AR-15 LPK - Basic Ambi Build Kit (AR15-LP-KT-03) — product page (same note on KAK's M16 ambi lower-parts-kit pages) — KAK Industry secondary
    https://kakindustry.com/basic-ambi-build-lower-parts-kit
32. AT3 Tactical SPEAR M-LOK Handguard — Installation Instructions (INSTR-SPEAR-03, Rev 3 Oct 18 2021) — AT3 Tactical secondary
    https://media.at3tactical.com/wp-content/uploads/spear_handguard_instructions_printsize-Rev-3-Oct-18-2021.pdf
33. Magpul MAG672 PRS GEN3 Stock — Installation Instructions (072-0115-A) — Magpul Industries Corp. secondary
    https://magpul.com/media/wysiwyg/Instructions/MAG672_PRS_GEN3_Stock_INSRT.pdf
34. Magpul UBR GEN2 Collapsible Stock — Installation & Usage Instructions for the AR15/M4 & SR25/M110 (072-0105-B) — Magpul Industries Corp. secondary
    https://magpul.com/media/wysiwyg/Instructions/MAG482_UBR_GEN2_Stock%20INSRT.pdf
35. AR Lower Receiver Build: Pivot Pin Installation — Shooting Illustrated (NRA) secondary
    https://www.shootingillustrated.com/content/ar-lower-receiver-build-pivot-pin-installation/
36. TM 9-1005-249-23&P, Rifle, 5.56mm, M16 and M16A1 (unit and direct support, incl. RPSTL) — Department of the Army primary
    https://archive.org/download/ArmyTechnicalManualforM16Rifle-Tm9-1005-249-23p/Manual-Tm9-1005-249-23p_djvu.txt
37. TFB Armorer's Bench: Complete AR15 Assembly - Lower Receiver — The Firearm Blog secondary
    https://www.thefirearmblog.com/blog/2022/07/31/tfb-armorers-bench-complete-ar15-assembly-lower-receiver/

Educational guide only. Some information comes from non-authoritative sources. Always consult your manufacturer's manual and a licensed gunsmith. Verify your firearm is unloaded before every procedure. Full disclaimer: https://github.com/Fundamental-build-LLC/Pew-Takedown

Legal notice: this material is third-party information compiled from sources of varying reliability and is provided for general informational and educational purposes only. It is not gunsmithing, technical, safety or legal advice, it is not verified or endorsed by any manufacturer, and it must not be taken as fact. Any work on a firearm beyond the routine field stripping described in its own owner's manual should be performed only by a licensed and insured gunsmith. You use this material entirely at your own risk. Fundamental Build LLC and the project's contributors make no warranty of any kind and accept no liability for death, injury, damage or loss arising from its use. Full terms: LEGAL.md.