Pew-Takedown
Guide only. 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. Read the full disclaimer.

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AR-15 (M16/M4 Pattern)

field strip ~2 min · reassembly ~3 min · detail strip ~25 min

Before you begin Verify this firearm is unloaded. Remove the magazine or empty the cylinder or tube, lock the action open, and check the chamber both by sight and by touch. Keep the muzzle in a safe direction and remove all live ammunition from your work area.

Specifications

Manufacturer
AR-15 Pattern (multiple manufacturers)
Origin
United States
Category
Rifle
Action
Gas, direct impingement
Calibers
5.56x45mm NATO, .223 Remington, 300 AAC Blackout, 6.5 Grendel, .224 Valkyrie
Capacity
30+1 with a standard STANAG magazine
Production
1959–present (in-production)
Also known as
M16, M4 Carbine, AR-15A2, MSR

Model-specific safety

If it will not go back together

Common ways this firearm resists reassembly, and what is actually wrong. Forcing a part that will not seat is how firearms get damaged.

  • The firing pin retaining pin will not go in.

    Why The cam pin is missing, or is in but not rotated 90 degrees.

    Fix Drop the cam pin into its hole and rotate it a quarter turn, then seat the firing pin and fit the retaining pin.

    Forcing it Never force the firing pin. If the cam pin is unrotated the bolt cannot lock and the rifle is unsafe to fire.

Under spring tension

Easily lost parts

Bolt cam pin · Firing pin retaining pin (cotter pin) · Extractor pin · Buffer retainer and its spring

Tools

ToolRequiredUsed forSubstitute
Punch or a cartridge rimOptionalPushing out stubborn takedown pins on a tight rifle.The rim of a fired case, or the tip of a bullet on a loaded round — though using ammunition as a tool is a habit worth avoiding.
Small punch or paperclipOptionalRemoving the firing pin retaining pin from the bolt carrier group.

Shop difficulty

Shop tier 2 Tier 2 — moderate among rifles and carbines, for the full job: strip to the parts that get coated and put it back together working. 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.

Parts: 92 numbered 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-), from 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, p. Appendix C Section II, pp. C-1-1 to C-14 archive.org [11].

Bench time: about 40 min to strip, 60 min to rebuild (estimate). Estimate: full lower strip (fire control, bolt catch, mag catch, selector, detents, buffer/stock, trigger guard), BCG strip, upper strip (EPC, forward assist, charging handle, handguard, gas block, barrel off with wrench and vise block, muzzle device). Rebuild longer: detents, roll pins, port cover spring, barrel nut torque and gas tube indexing, function check.

Small parts: 18 pins, 19 springs, 6 detents or plungers (counted by name in the same list, as line items (M16A1, auto parts excluded). Pins = every 'PIN,...' entry except the firing pin (cam pin, firing pin retaining pin, extractor pin, spring pins, grooved)

What comes off for coating

Special tools

Known pain points

See also 1 documented reassembly problem and their fixes.

Fit or check on rebuild

This is Pew-Takedown's rating, not the manufacturer's. How tiers are rated. Forum reports are owners' experience, not specifications.

Procedures

Clear and Make Safe

Clear & 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.
    Removed at this step: 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.
    WarningCheck 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.
    TipOnce the upper and lower are separated, selector position no longer matters for disassembly.
  6. Remove all live ammunition from the work area.

Field Strip

Field Strip

Separate the upper and lower, then remove the bolt carrier group and charging handle. No tools on most rifles.

  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.
    TipIf 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.
    TipYou can stop here for most cleaning. Separating the receivers is optional if you only want to reach the bolt.
    Removed at this step: Upper receiver assembly
  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.
    Removed at this step: Bolt carrier group
    Bolt carrier assembly
    Bolt carrier assembly Carrier, key, bolt, cam pin and firing pin retaining pin — the parts that come apart during a field strip. TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1, p.176 — Headquarters, Department of the Army. Source. Public domain (US Government work).
  6. With the carrier out, pull the charging handle down and out of its channel in the upper receiver.
    WarningThe charging handle must come out after the carrier, not before. It will not clear its channel otherwise.
    Removed at this step: Charging handle
    Charging handle assembly
    Charging handle assembly The latch, its spring and roll pin. Relevant if the latch has stopped holding. TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1, p.179 — Headquarters, Department of the Army. Source. Public domain (US Government work).

Disassemble the Bolt Carrier Group

Detail Strip tools required

Routine — this is part of normal cleaning on a direct-impingement rifle.

  1. Remove the firing pin retaining pin (a small cotter pin) from the side of the carrier using a punch or your fingers.
    TipIt only needs to come out far enough to clear the firing pin — do not fully remove and lose it.
    Removed at this step: Firing pin retaining pin
  2. Tip the carrier back and let the firing pin drop out of the rear.
    WarningDo not pry the firing pin out. If it will not drop, the bolt is not pushed forward.
    Removed at this step: Firing pin
  3. Push the bolt forward into the carrier, rotate the cam pin 90 degrees, and lift it straight out.
    WarningThe cam pin is the single most important part not to lose. A rifle assembled without it is dangerous.
    Removed at this step: Cam pin
  4. Pull the bolt straight out of the front of the carrier.
    Removed at this step: Bolt
  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.
    WarningThe extractor spring has a rubber or polymer insert that must not be removed or lost — it provides part of the extractor tension.
    Removed at this step: Extractor Extractor spring and insert
  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

Detail Strip
  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.
    WarningThe buffer is under spring pressure and will launch forward. Keep a hand on it and wear eye protection.
    TipMake 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.
    Removed at this step: Buffer Buffer spring
  4. 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.
    WarningConfirm 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.

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

Detail Strip tools required gunsmith recommended

TM 9-1005-319-23&P para 2-17a, steps 1–6. The TM's step 7 (buffer and action spring) is the entry's existing 'buffer-removal'. Unit maintenance (chapter 2) — above operator level.

Follows 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, para 2-17a (pp. 2-57 to 2-59) archive.org [5]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  1. Separate the upper receiver from the lower receiver (entry's field strip).
  2. Remove the pistol grip screw and lockwasher.
    Removed at this step: Screw Lockwasher
  3. Carefully remove the pistol grip and catch the helical spring and safety detent.
    WarningTo avoid injury to your eyes, use care when removing and installing spring-loaded parts.
    Removed at this step: Pistol grip Helical spring Safety detent
  4. Fixed rifle stock: remove the self-locking buttstock screw.
    WarningIf the self-locking screw is removed, it must be discarded and replaced with a new one.
    Removed at this step: Self-locking screw
  5. Fixed rifle stock: remove the buttstock assembly carefully and catch the helical spring, takedown pin detent, takedown pin and stepped spacer.
    WarningTo avoid injury to your eyes, use care when removing and installing spring-loaded parts.
    TipIf the detent will not come out, use a wire to push it out.
    Removed at this step: Buttstock assembly Helical spring Takedown pin detent Takedown pin Stepped spacer
  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.
    Removed at this step: Buttstock assembly
  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.
    WarningTo avoid injury to your eyes, use care when removing and installing spring-loaded parts.
    Removed at this step: Pivot pin
  8. Hold a cupped hand in front of the pivot pin detent and helical spring as the pin comes out, to catch them.
    TipIf the helical spring will not come out, use a wire to pull it out.
    Removed at this step: Pivot pin detent Helical spring

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

Detail Strip tools required gunsmith recommended

TM 9-1005-249-23&P para 3-16a (M16/M16A1), the semiautomatic parts only. Pistol grip and buttstock come off first (TM 9-1005-319-23&P para 3-13 lists them as removed). Direct support maintenance (chapter 3).

Follows 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, para 3-16a (pp. 3-50 to 3-52) archive.org [11]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  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.
    Removed at this step: Spring pin
  3. Remove the bolt catch, bolt catch plunger and bolt catch spring.
    Removed at this step: Bolt catch Bolt catch plunger 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.
    WarningTo avoid injury to your eyes, use care when removing and installing spring-loaded parts.
    Removed at this step: Magazine catch
  5. Remove the magazine button and magazine catch spring.
    Removed at this step: Magazine button Magazine catch spring
  6. Remove the safety selector lever.
    TipAt this point the military rifle has an additional part that the semiautomatic AR-15 does not have; it is not covered here.
    Removed at this step: Safety selector lever
  7. With the hammer forward, push the hammer pin out of the lower receiver with a drive pin punch.
    WarningTo avoid injury to your eyes, use care when removing and installing spring-loaded parts.
    TipIf the selector lever is still installed, the TM places it on SEMI for this step.
    Removed at this step: Hammer pin
  8. Remove the hammer assembly.
    Removed at this step: Hammer assembly
  9. Push the trigger pin out from the left side of the lower receiver with a drive pin punch.
    Removed at this step: Trigger pin
  10. Remove the disconnector and trigger assembly from the lower receiver.
    Removed at this step: Disconnector Trigger assembly

Remove the hammer and trigger springs

Detail Strip gunsmith recommended

TM 9-1005-249-23&P paras 3-17a and 3-18a, after the hammer and trigger are out of the receiver. Direct support maintenance (chapter 3).

Follows 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, para 3-18a (p. 3-61) archive.org [11]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  1. Remove the hammer spring from the hammer.
    Removed at this step: Hammer spring
  2. Remove the disconnector spring and trigger spring from the trigger.
    WarningTo avoid injury to your eyes, use care when removing and installing spring-loaded parts.
    Removed at this step: Disconnector spring Trigger spring

Remove the trigger guard and lower receiver extension

Detail Strip tools required gunsmith recommended

TM 9-1005-319-23&P para 3-16a, rifle and carbine. Buffer, action spring and buttstock come out first. Direct support maintenance (chapter 3).

Follows 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, para 3-16a (pp. 3-77 to 3-78.1) archive.org [5]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  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.
    Removed at this step: Spring pin
  3. Remove the trigger guard.
    Removed at this step: 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.
    WarningTo avoid injury to your eyes, use care when removing and installing spring-loaded parts.
    Removed at this step: Lower receiver extension Buffer retainer Helical spring
  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.
    Removed at this step: Locking nut
  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.
    WarningRestrain the pivot pin spring and detent while doing this (TM caution).
    Removed at this step: Lower receiver extension Receiver end plate Buffer retainer Helical spring

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

Detail Strip tools required gunsmith recommended

TM 9-1005-319-23&P para 2-16a. Each item comes off only when it needs repair or replacement, as the TM's notes say. Unit maintenance (chapter 2) — above operator level.

Follows 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, para 2-16a (pp. 2-45 to 2-48) archive.org [5]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  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.
    WarningDo 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.
    TipThe operator's manual describes a 'buddy system' for this.
    Removed at this step: Upper handguard assembly
  3. Push down on the handguard slip ring and lift the lower handguard assembly up and out.
    Removed at this step: Lower handguard assembly
  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.
    WarningTo avoid injury to your eyes, use care when removing and installing spring-loaded parts.
    Removed at this step: Front sight post
  5. Catch the front sight detent and helical spring.
    Removed at this step: Front sight detent 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.
    Removed at this step: Small sling swivel Tubular 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.
    Removed at this step: Spring pins Swivel locking bar Swivel mount Front swivel
  8. Only if repair is necessary: remove the retaining ring and slide the headless grooved pin out to the rear.
    TipThe pin may bind against the forward assist housing and need some extra force.
    Removed at this step: Retaining ring Headless grooved pin
  9. Catch the cover spring and ejection port cover as the pin comes out.
    Removed at this step: Cover spring Ejection port cover

Remove the gas tube, compensator and barrel

Detail Strip tools required gunsmith recommended

TM 9-1005-319-23&P para 3-10a (M16A2 / M4): gas tube, compensator and peel washer, then the barrel nut is loosened and the barrel separated from the upper receiver. Barrel work affects headspace. Direct support maintenance (chapter 3).

Follows 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, para 3-10a (pp. 3-30 to 3-33) archive.org [5]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  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.
    Removed at this step: Spring pin
  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.
    Removed at this step: Gas tube
  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.
    Removed at this step: Compensator
  6. Remove the peel washer without losing or bending its thin sections.
    Removed at this step: Peel washer
  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.
    WarningDo not use a torque wrench to loosen the barrel nut assembly.
  9. Separate the upper receiver assembly from the barrel assembly.
    Removed at this step: Upper receiver assembly Barrel assembly
  10. Remove the barrel assembly from the vise and barrel removal fixture.
  11. Remove the retaining ring with retaining ring pliers.
    Removed at this step: Retaining ring
  12. Remove the slip ring spring and handguard slip ring.
    WarningDo not remove the barrel nut from the barrel assembly.
    Removed at this step: Slip ring spring Handguard slip ring

Remove the A2 rear sight and the forward assist

Detail Strip tools required gunsmith recommended

TM 9-1005-319-23&P para 3-11a: the M16A2-style adjustable rear sight in the carrying handle, then the forward assist. Direct support maintenance (chapter 3).

Applies to: Upper receivers with the fixed carrying handle and A2 rear sight (M16A2 / A2-pattern AR-15). Flat-top receivers have no sight to remove here.

Follows 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, para 3-11a (pp. 3-48 to 3-51) archive.org [5]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  1. Drive out the windage knob spring pin with a hammer and 1/16-inch punch.
    WarningBe sure to catch the small parts.
    Removed at this step: Spring pin
  2. Catch the rear sight windage knob, helical spring and ball bearing.
    Removed at this step: Windage knob Helical spring Ball bearing
  3. Remove the rear sight windage screw with a flat-bladed screwdriver.
    Removed at this step: Windage screw
  4. Remove the sight aperture and flat spring from the upper receiver.
    Removed at this step: Sight aperture Flat spring
  5. Drive out the elevation spring pin with a 3/32-inch punch and catch the helical spring as the punch is withdrawn.
    WarningTo avoid injury to your eyes, use care when removing and installing spring-loaded parts.
    Removed at this step: Spring pin Helical spring
  6. Rotate the elevation index until the rear sight base clears the upper receiver, catching the ball bearing and helical spring as it clears.
    Removed at this step: Rear sight base Ball bearing Helical spring
  7. Push the elevation index out with your thumb using a slight rotating motion, and catch the ball bearing and helical spring.
    Removed at this step: Elevation knob assembly Ball bearing 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.
    Removed at this step: Index screw Elevation index Elevation knob
  9. Remove the forward assist spring pin with a 3/32-inch drive pin punch and hand hammer.
    Removed at this step: Pin
  10. Remove the forward assist assembly and its helical spring from the upper receiver.
    WarningTo avoid injury to your eyes, use care when removing and installing spring-loaded parts.
    Removed at this step: Forward assist assembly Helical spring

Disassemble the forward assist

Detail Strip tools required gunsmith recommended

TM 9-1005-319-23&P para 3-12a, after the forward assist is out of the upper receiver. Direct support maintenance (chapter 3).

Applies to: Upper receivers with a forward assist.

Follows 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, para 3-12a (p. 3-59) archive.org [5]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  1. Drive out the spring pin with a 1/16-inch drive pin punch and hand hammer.
    WarningTo avoid injury to your eyes, use care when removing and installing spring-loaded parts.
    Removed at this step: Spring pin
  2. Remove the forward assist pawl, pawl detent and helical spring from the plunger assembly.
    Removed at this step: Forward assist pawl Pawl detent Helical spring

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

Detail Reassembly tools required gunsmith recommended

TM 9-1005-319-23&P para 2-17f, steps 2–8. The TM's step 1 (buffer and action spring) is in the entry's 'buffer-removal' procedure. Unit maintenance (chapter 2) — above operator level.

Follows 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, para 2-17f (pp. 2-62 to 2-64) archive.org [5]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  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.
    WarningTo 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.
    TipThe 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.
    WarningDo 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.
    WarningDo 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.
    WarningWith 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.
    TipPart of the helical spring fits into a hole in the pistol grip.

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

Detail Reassembly tools required gunsmith recommended

TM 9-1005-249-23&P para 3-16g, the semiautomatic parts only. Direct support maintenance (chapter 3).

Follows 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, para 3-16g (pp. 3-58 to 3-60) archive.org [11]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  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.
    TipTM 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.
    WarningTo 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.
    TipTM 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.
    TipTM 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

Detail Reassembly gunsmith recommended

TM 9-1005-249-23&P paras 3-17c and 3-18c. Direct support maintenance (chapter 3).

Follows 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, para 3-18c (p. 3-62) archive.org [11]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  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

Detail Reassembly tools required gunsmith recommended

TM 9-1005-319-23&P para 3-16d. The torque values (rifle extension 35–39 ft-lb; carbine locking nut 40 ±2 in-lb) are already in the entry's torqueSpecs. Direct support maintenance (chapter 3).

Follows 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, para 3-16d (pp. 3-80 to 3-82) archive.org [5]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  1. Fixed rifle stock: install the helical spring and buffer retainer into the lower receiver.
    WarningTo 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

Detail Reassembly tools required gunsmith recommended

TM 9-1005-319-23&P para 2-16f. Unit maintenance (chapter 2) — above operator level.

Follows 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, para 2-16f (pp. 2-52 to 2-56) archive.org [5]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  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.
    TipThe 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.
    WarningTo 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

Detail Reassembly tools required gunsmith recommended

TM 9-1005-319-23&P para 3-10d–e. The barrel nut (30 ft-lb three times, 80 ft-lb ceiling) and compensator (15–20 ft-lb) torques are already in the entry's torqueSpecs. After a barrel change the TM requires a headspace check, test firing and re-zeroing. Direct support maintenance (chapter 3).

Follows 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, para 3-10d (pp. 3-39 to 3-45) archive.org [5]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  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.
    TipThe 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.
    TipThe 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.
    WarningMake 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.
    TipIf 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.
    WarningNever 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.
    WarningHeadspace 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

Detail Reassembly tools required gunsmith recommended

TM 9-1005-319-23&P para 3-11e, including setting elevation and checking the 300 m zero mark. Direct support maintenance (chapter 3).

Applies to: Upper receivers with the fixed carrying handle and A2 rear sight (M16A2 / A2-pattern AR-15).

Follows 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, para 3-11e (pp. 3-54 to 3-57) archive.org [5]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  1. Apply CLP to the helical spring and forward assist assembly and install them in the upper receiver.
    WarningTo 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.
    WarningDo 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.
    TipAll 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.
    WarningThe 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.
    TipTilt 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

Detail Reassembly tools required gunsmith recommended

TM 9-1005-319-23&P para 3-12e. Direct support maintenance (chapter 3).

Applies to: Upper receivers with a forward assist.

Follows 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, para 3-12e (p. 3-61) archive.org [5]

Gunsmith recommendedThis procedure can affect how safely the firearm functions. If you are not confident, stop here and take it to a licensed gunsmith.
  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.
    WarningTo 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

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.
    WarningIf 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.
    WarningThis 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.

Diagrams

public domain

These are reproduced from government technical manuals, which are not subject to copyright. Manufacturer manual diagrams are not reproduced here — the entry links to the manual instead.

M16 rifle, complete exploded view
M16 rifle, complete exploded view The whole rifle broken into its groups. Useful for seeing where a part you are holding belongs before you go looking for it. TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1, p.175 — Headquarters, Department of the Army. Source. Public domain (US Government work).
Upper receiver and barrel assembly
Upper receiver and barrel assembly Handguards, barrel, front sight base, gas tube and flash hider laid out in order. Figure C-6 in the manual. TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1, p.180 — Headquarters, Department of the Army. Source. Public domain (US Government work).
Lower receiver and extension assembly
Lower receiver and extension assembly Fire control parts, buffer, buffer spring and receiver extension. Figure C-10 in the manual. TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1, p.188 — Headquarters, Department of the Army. Source. Public domain (US Government work).
Bolt carrier assembly
Bolt carrier assembly Carrier, key, bolt, cam pin and firing pin retaining pin — the parts that come apart during a field strip. TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1, p.176 — Headquarters, Department of the Army. Source. Public domain (US Government work).
Bolt assembly
Bolt assembly Bolt body, extractor and its spring, ejector, and the gas rings. What you are looking at once the bolt is out of the carrier. TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1, p.177 — Headquarters, Department of the Army. Source. Public domain (US Government work).
Charging handle assembly
Charging handle assembly The latch, its spring and roll pin. Relevant if the latch has stopped holding. TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1, p.179 — Headquarters, Department of the Army. Source. Public domain (US Government work).
Figure C-7 — (M16A2) Barrel assembly and (M4/M4A1) replacement barrel and front sight assembly
Figure C-7 — (M16A2) Barrel assembly and (M4/M4A1) replacement barrel and front sight assembly Barrel, barrel nut, slip ring and spring, front sight base, sight post and detent, gas tube and compensator with key numbers — the exploded view for barrel removal and installation. TM 9-1005-319-23&P (AF TO 11W3-5-5-42) Unit and Direct Support Maintenance Manual (Including Repair Parts and Special Tools List): Rifle, 5.56mm, M16A2; Carbine, 5.56mm, M4 and M4A1, p.271 — Departments of the Army and Air Force. Source. Public domain (US Government work).
Figure C-8 — Upper receiver assembly (M16A2; M4/M4A1)
Figure C-8 — Upper receiver assembly (M16A2; M4/M4A1) The upper receiver's own parts — ejection port cover and spring, forward assist, rear sight parts — for the upper receiver strip and the ejection port cover spring orientation. TM 9-1005-319-23&P (AF TO 11W3-5-5-42) Unit and Direct Support Maintenance Manual (Including Repair Parts and Special Tools List): Rifle, 5.56mm, M16A2; Carbine, 5.56mm, M4 and M4A1, p.273 — Departments of the Army and Air Force. Source. Public domain (US Government work).
Figure C-10 — (M16A2) Rear sight assembly
Figure C-10 — (M16A2) Rear sight assembly Windage knob, screw, aperture, flat spring, elevation knob and index, ball bearings and springs — which spring and ball goes where in the A2 rear sight. TM 9-1005-319-23&P (AF TO 11W3-5-5-42) Unit and Direct Support Maintenance Manual (Including Repair Parts and Special Tools List): Rifle, 5.56mm, M16A2; Carbine, 5.56mm, M4 and M4A1, p.277 — Departments of the Army and Air Force. Source. Public domain (US Government work).
Figure C-16 — (M16A2) Lower receiver and receiver extension assembly
Figure C-16 — (M16A2) Lower receiver and receiver extension assembly Receiver extension, buffer retainer and spring, trigger guard and its pin — the parts of the receiver-extension procedures (Figure C16A on pdfPage 294 is the carbine version with end plate and locking nut). TM 9-1005-319-23&P (AF TO 11W3-5-5-42) Unit and Direct Support Maintenance Manual (Including Repair Parts and Special Tools List): Rifle, 5.56mm, M16A2; Carbine, 5.56mm, M4 and M4A1, p.292 — Departments of the Army and Air Force. Source. Public domain (US Government work).

Torque specifications

Use a calibrated torque driverValues are the manufacturer's, shown in the unit it gives first; conversions are calculated and rounded. Tighten to the stated value — not "until it feels right" — and follow any sequence noted.
FastenerTorqueSequence, notes and the source's wordsWhere it comes from
Barrel nut — seating torque
Mil-spec pattern barrel nut (delta-ring type)		 30 ft-lb
40.7 N·m · 360 in-lb

Engage the barrel nut threads with the upper receiver. With the combination wrench's three drive pins fully engaged and the torque wrench read with both wrenches together, torque to 30 ft-lb, loosen, repeat, loosen again, then torque a third time to 30 ft-lb while keeping sight alignment. The TM: two-time torquing (three times total) gives a better thread fit and keeps barrel nuts from loosening. Never use the torque wrench to loosen.

“Using combination wrench (9) and torque wrench, torque barrel nut assembly (8) to 30 ft-lb.”

 TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1 — Headquarters, Department of the Army, p. 3-31 archive.org [4]
Barrel nut — ceiling when aligning for the gas tube
Mil-spec pattern barrel nut (delta-ring type)		 max. 80 ft-lb
108.5 N·m · 960 in-lb

After the third 30 ft-lb torque, the nut may be tightened beyond 30 ft-lb to bring the next serration in line with the gas tube hole. Never loosen the barrel nut to align it — tighten to the next hole instead, and not past this ceiling.

“Do not torque over 80 ft-lb while tightening the barrel nut to next hole, to allow for proper alignment.”

 TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1 — Headquarters, Department of the Army, p. 3-33 archive.org [4]
Flash suppressor
M16/M16A1 flash suppressor		 15–20 ft-lb
20.3–27.1 N·m · 180–240 in-lb

Torque is measured with both wrenches used together.

“Torque flash suppressor (15) to 15-20 ft-lb using combination wrench (9) and torque wrench.”

 TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1 — Headquarters, Department of the Army, p. 3-34 archive.org [4]
Carrier key screws (2) 35–40 in-lb
4–4.5 N·m · 2.9–3.3 ft-lb

Hold the carrier in a machinist's vise with jaw caps. Do not reuse old screws. The screws are staked afterwards; the TM also says not to retorque screws whose staking marks show no loosening.

“Use a socket head screw wrench attachment and torque wrench to torque the carrier and key screws (3) to 35 to 40 inch-pounds.”

 TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1 — Headquarters, Department of the Army, p. 3-20 archive.org [4]
Lower receiver extension (buffer tube)
Fixed rifle-stock receiver extension (M16/M16A1)		 35–39 ft-lb
47.5–52.9 N·m · 420–468 in-lb

Clamp the solid portion of the lower receiver and extension assembly in a vise, with wooden jaws if available. Torque is read with both wrenches used together.

“Using combination wrench 11010033 (6) and torque wrench, torque lower receiver extension to 35-39 ft-lb.”

 TM 9-1005-249-23&P — Unit and Direct Support Maintenance Manual, Rifle, 5.56mm, M16 and M16A1 — Headquarters, Department of the Army, p. 3-67 archive.org [4]
Receiver end plate locking nut (castle nut) on lower receiver extension
M4/M4A1 carbine (TM section headed 'CARBINE ONLY'); tolerance ±2 in-lb per source		 40 in-lb
4.5 N·m · 3.3 ft-lb

6A. Lubricate threads of lower receiver and extension with molybdenum disulfide grease. 6B. Screw locking nut onto the extension, three notches facing forward. 6C. Align receiver end plate lug forward. 6E. Screw extension in until it retains the buffer retainer. 6F. Screw the locking nut forward until it contacts the receiver end plate. 6G. Tighten the locking nut until snug with the special tool. 6H. Torque to 40 ±2 inch pounds. 6J. Stake the receiver end plate in 2 places across from the notches in the locking nut.

“6H. Using the special tool (item 12, app C), and torque wrench, torque locking nut (5.5) to 40 ±2 inch pounds.”

 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, p. 3-81.1, Change 3 (PDF p. 200) archive.org [5]
Compensator (muzzle device)
M16A2 rifle / M4-series (TM 9-1005-319-23&P), compensator with peel washer		 15–20 ft-lb
20.3–27.1 N·m · 180–240 in-lb

14. Install peel washer and compensator on rifle barrel assembly. 15. Torque compensator to 15-20 ft-lb using combination wrench and torque wrench (torque measured when both wrenches are used together). Some portion of the opening of the third or middle slot must be straight up (align with the front sight post) at proper torque level. Thin sections of the peel washer may be removed or added as required.

“Torque compensator (12) to 15-20 ft-lb (20-27 N-m) using combination wrench (10) and torque wrench. Torque is measured when both wrenches are used together.”

 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, p. 3-44, Change 4 (PDF p. 158) archive.org [5]

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.

Reported by other sources — not the manufacturer

Not a manufacturer specificationThese values come from the people and publications named beside each one, not from AR-15 Pattern (multiple manufacturers), and where they differ from the manufacturer's values above, the manufacturer wins. They are recorded with who said them and their exact words so you can judge them — not as a recommendation. Confirm any of them with the manufacturer or a licensed gunsmith before you put a wrench on your firearm; a wrong value can crack a stock, strip a thread or loosen a muzzle device.
FastenerTorqueWho says so, and their wordsWhere it comes from
Receiver extension lock (castle) nut
AR15/M4 carbine receiver extension, when fitting Magpul's ASAP end plate		 40 ft-lb
54.2 N·m · 480 in-lb

Reported by Magpul Industries
Secondary — a parts or tool maker, or a gunsmithing publisher

Screw the receiver extension in while holding the end plate and buffer retaining pin; install the locking key; hand tighten the locking nut, then torque. Source states a tolerance of ± 2 foot lbs.

Threadlocker: DO NOT USE LOCTITE® OR OTHER LOCKING COMPOUND ON RECEIVER EXTENSION THREADS.

“With the armorers/spanner wrench, tighten the locking nut down to 40 ± 2 foot lbs. torque per US Army TM 9-1005-319-23&P Unit and Direct Support Maintenance Manual (3-81.1).”

 ASAP (Ambidextrous Sling Attachment Point) Installation Instructions — Magpul Industries, PDF p. 1 magpul.com [6]
Barrel nut (Geissele aluminium barrel nut supplied with the SMR MK8 handguard)
AR-15/M4 mil-spec flat-top upper fitted with a Geissele SMR MK8 M-LOK handguard		 40 ft-lb
54.2 N·m · 480 in-lb

Reported by Geissele Automatics (document hosted by MidwayUSA)
Secondary — a parts or tool maker, or a gunsmithing publisher

Liberally coat the upper receiver threads and the outer face (torque shoulder) of the barrel extension with anti-seize or grease; hand tighten the Geissele barrel nut, then torque with the Geissele wrench.

“Use the Geissele barrel nut wrench to tighten the Geissele barrel nut to 40 ft-lbs by using the pin and corresponding hole in the OD of the barrel nut.”

 Installation Instructions — Geissele Super Modular Rail, MK8 Magpul M-LOK Rails — Geissele Automatics (document hosted by MidwayUSA), PDF p. 1 media.midwayusa.com [7]
Handguard (rail) mounting/clamp bolts (2)
Geissele SMR MK8 M-LOK handguard on AR-15/M4		 5 ft-lb
6.8 N·m · 60 in-lb

Reported by Geissele Automatics (document hosted by MidwayUSA)
Secondary — a parts or tool maker, or a gunsmithing publisher

Keep the scope mount installed during the tightening process. If a torque wrench is not available use a short arm allen key and tighten snug.

“Tighten the two rail mounting bolts to 5.0 ft-lbf.”

 Installation Instructions — Geissele Super Modular Rail, MK8 Magpul M-LOK Rails — Geissele Automatics (document hosted by MidwayUSA), PDF p. 1 media.midwayusa.com [7]
Barrel nut (Midwest Industries free-float handguard barrel nut)
AR-15 fitted with a Midwest Industries free-float M-LOK handguard		 40 ft-lb
54.2 N·m · 480 in-lb

Reported by Midwest Industries, Inc.
Secondary — a parts or tool maker, or a gunsmithing publisher

“Set your torque wrench to 40 ft/lbs. Hold the barrel nut wrench tightly against the barrel nut and torque to 40 ft/lbs.”

 Free Float Hand Guard Installation Instructions — Midwest Industries, Inc., PDF p. 1 midwestindustriesinc.com [8]
Handguard clamp screws, 10-32 x ½" socket head (with MI torque plate)
Midwest Industries free-float handguard on AR-15		 40 in-lb
4.5 N·m · 3.3 ft-lb

Reported by Midwest Industries, Inc.
Secondary — a parts or tool maker, or a gunsmithing publisher

Drop the torque plate into the slot, finger tighten the bolts, torque, then check receiver/handguard rail alignment.

“Torque the 10-32 x ½” socket head cap screw to 40 in/lbs.”

 Free Float Hand Guard Installation Instructions — Midwest Industries, Inc., PDF p. 1 midwestindustriesinc.com [8]
Barrel nut — thread-conditioning passes (BCM KMR barrel nut)
Mil-spec direct-impingement AR-15 (.223/5.56) fitted with a BCM KMR-series handguard (KMR-A, MCMR, QRF)		 20–30 ft-lb
27.1–40.7 N·m · 240–360 in-lb

Reported by Bravo Company MFG (BCM)
Secondary — a parts or tool maker, or a gunsmithing publisher

Torque to 20-30 ft-lbs then loosen; repeat a minimum of 4 times for optimal thread engagement and fit. NEVER use the torque wrench for loosening the barrel nut. Then final-torque to 40-50 ft-lbs.

“properly align wrench and torque the KMR barrel nut to 20-30 ft-lbs while applying pressure to the wrench in the direction shown.”

 Installation Manual for BCM KMR Series Handguards (KMR-A, MCMR, QRF), Rev. 4/21 — Bravo Company MFG (BCM), p. 2 bravocompanymfg.com [9]
Barrel nut — final installation (BCM KMR barrel nut)
Mil-spec direct-impingement AR-15 (.223/5.56) fitted with a BCM KMR-series handguard (KMR-A, MCMR, QRF)		 40–50 ft-lb
54.2–67.8 N·m · 480–600 in-lb

Reported by Bravo Company MFG (BCM)
Secondary — a parts or tool maker, or a gunsmithing publisher

“Final installation of the KMR barrel nut should be 40-50 ft-lbs.”

 Installation Manual for BCM KMR Series Handguards (KMR-A, MCMR, QRF), Rev. 4/21 — Bravo Company MFG (BCM), p. 2 bravocompanymfg.com [9]
Handguard cross bolts (notched and locking)
BCM KMR-series handguard on AR-15		 30–40 in-lb
3.4–4.5 N·m · 2.5–3.3 ft-lb

Reported by Bravo Company MFG (BCM)
Secondary — a parts or tool maker, or a gunsmithing publisher

Degrease the threaded ends of the cross bolts and apply the supplied thread locker; tighten the notched cross bolt so its notch aligns with the adjacent screw hole, then tighten the locking cross bolt (30-40 in-lbs). NEVER over tighten.

Threadlocker: Apply the supplied thread locker to the threaded ends of the cross bolts.

“Continue to tighten the notched cross bolt to 30-40 in-lbs. so that the notch in the head aligns with the adjacent screw hole as shown in Figure 4.”

 Installation Manual for BCM KMR Series Handguards (KMR-A, MCMR, QRF), Rev. 4/21 — Bravo Company MFG (BCM), p. 2 bravocompanymfg.com [9]
Barrel nut (Aero Precision BAR barrel nut, for Enhanced/Quantum handguards on standard threaded uppers)
AR15 standard threaded upper receiver with Aero Precision BAR barrel nut		 30–45 ft-lb
40.7–61 N·m · 360–540 in-lb

Reported by Aero Precision
Secondary — a parts or tool maker, or a gunsmithing publisher

Apply anti-seize grease to the upper receiver threads. Torque to 30 ft. lbs, remove and re-torque; repeat three times to condition the threads. Use shims to time the gas-tube hole at 12 o'clock; 'Torqueing BAR Barrel Nut over 45 ft. lbs. can result in damage to your barrel nut.'

“*Recommended torgue 30-45 ft. lbs.”

 AR15 BAR Barrel Nut Installation — Aero Precision, PDF p. 1 aeroprecisionusa.com [10]
Barrel nut (Aero Precision ATLAS taper-lock handguard barrel nut)
AR-15 upper receiver with an Aero Precision ATLAS (Aero Taper Lock Attachment System) handguard		 35–60 ft-lb
47.5–81.3 N·m · 420–720 in-lb

Reported by Aero Precision
Secondary — a parts or tool maker, or a gunsmithing publisher

Coat the upper-receiver threads with anti-seize or grease first; align the nut with the receiver and use shims if needed to reach alignment inside the range.

“use the provided barrel nut wrench to torque to 35 – 60ftlbs. Use provided shims if necessary.”

 ATLAS (Aero Taper Lock Attachment System) Installation Instructions — Aero Precision, PDF p. 1, step 2 aeroprecisionusa.com [12]
Barrel nut (Aero Precision R-ONE / S-ONE handguard barrel nut)
AR15 / M4E1 upper receiver with an Aero Precision ATLAS R-ONE or S-ONE handguard		 35–65 ft-lb
47.5–88.1 N·m · 420–780 in-lb

Reported by Aero Precision
Secondary — a parts or tool maker, or a gunsmithing publisher

Apply non-graphite anti-seize to the receiver threads; torque with the supplied wrench extension and align a gas-tube notch with the receiver gas-tube hole; if alignment is not reached inside the range, add supplied shims.

“Next, you will need to tighten your barrel nut to 35-65 ft lbs. using the supplied wrench extension.”

 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, p. article body support.aeroprecisionusa.com [13]
Barrel nut (Aero Precision MOD 4 steel barrel nut)
AR15 (M4E1 threaded or mil-spec AR-15 upper) with an Aero Precision MOD 4 M-LOK handguard		 55 ft-lb
74.6 N·m · 660 in-lb

Reported by Aero Precision
Secondary — a parts or tool maker, or a gunsmithing publisher

Stated as 55 +/- 5 ft-lb; the MOD 4 nut needs no gas-tube timing. The maker gives 55 ± 5.

“Barrel Nut Torque: 55 +/-5 FT LBS”

 MOD 4: 7 Sided M-LOK Handguard — Aero Precision product page — Aero Precision, p. Details > Features aeroprecisionusa.com [14]
Handguard screws (Aero Precision MOD 4)
AR15 with an Aero Precision MOD 4 M-LOK handguard		 55 in-lb
6.2 N·m · 4.6 ft-lb

Reported by Aero Precision
Secondary — a parts or tool maker, or a gunsmithing publisher

Stated as 55 +/- 5 in-lb. The maker gives 55 ± 5.

“Handguard Screw Torque - 55+/-5 in-lbs”

 MOD 4: 7 Sided M-LOK Handguard — Aero Precision product page — Aero Precision, p. Specifications > Other aeroprecisionusa.com [14]
Receiver extension castle nut
Aero Precision M4E1 lower receiver (AR15) build		 40 ft-lb
54.2 N·m · 480 in-lb

Reported by Aero Precision
Secondary — a parts or tool maker, or a gunsmithing publisher

Seat the receiver end plate against the receiver before torquing.

“Seat the receiver extension end plate against the upper receiver and tighten your castle nut to 40 ft-lbs”

 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, p. article body (buffer/stock section) support.aeroprecisionusa.com [15]
Barrel nut (Aero Precision C.O.P. barrel nut into the C.O.P. upper receiver)
AR-15 carbine / mid-length converted with the Aero Precision AR15 C.O.P. Kit (discontinued 2013 kit with its own upper receiver)		 55 ft-lb
74.6 N·m · 660 in-lb

Reported by Aero Precision
Secondary — a parts or tool maker, or a gunsmithing publisher

Grease the C.O.P. upper threads lightly; the barrel wrench must be fully seated on the nut lugs. The nut does not need indexing for the gas tube.

“Torque the barrel nut onto the upper receiver to 55 ft-lb.”

 Aero Precision C.O.P. Kit Manual (Proof 6, 09/03/2013) — AR15 C.O.P. Kit Assembly Manual — Aero Precision, PDF p. 6 (carbine) and p. 11 (mid-length aeroprecisionusa.com [16]
Handguard panel / rail-insert screws (C.O.P. kit, T-25 Torx)
AR-15 with the Aero Precision AR15 C.O.P. Kit		 25 in-lb
2.8 N·m · 2.1 ft-lb

Reported by Aero Precision
Secondary — a parts or tool maker, or a gunsmithing publisher

Lightly tighten all screws, then torque in an alternating pattern. Caution on the same page: do not exceed 40 in-lb (strips the screw holes).

“Then torque all screws in an alternating pattern to 25 in-lbs.”

 Aero Precision C.O.P. Kit Manual (Proof 6, 09/03/2013) — AR15 C.O.P. Kit Assembly Manual — Aero Precision, PDF p. 6 and p. 11, Kit Construction ste aeroprecisionusa.com [16]
Polymer Picatinny rail-section / accessory fasteners on the handguard
AR-15 with a BCM MCMR (M-LOK) handguard		 max. 20 in-lb
2.3 N·m · 1.7 ft-lb

Reported by Bravo Company MFG (BCM)
Secondary — a parts or tool maker, or a gunsmithing publisher

“Do NOT exceed 20 in/lbs. when securing fasteners on Polymer accessories.”

 BCM MCMR-13 (M-LOK Compatible Modular Rail) — product page — Bravo Company MFG (BCM), p. Description, 'Please note' bravocompanyusa.com [17]
Aluminum Picatinny rail-section fasteners on the handguard
AR-15 with a BCM MCMR (M-LOK) handguard		 30 in-lb
3.4 N·m · 2.5 ft-lb

Reported by Bravo Company MFG (BCM)
Secondary — a parts or tool maker, or a gunsmithing publisher

“Aluminum Picatinny rail sections may be torqued to 30 in/lbs.”

 BCM MCMR-13 (M-LOK Compatible Modular Rail) — product page — Bravo Company MFG (BCM), p. Description, 'Please note' bravocompanyusa.com [17]
M-LOK rail-section screws on the handguard
AR-15 with a Midwest Industries one-piece free-float handguard (same text in MI's CRM-HD instructions)		 15 in-lb
1.7 N·m · 1.2 ft-lb

Reported by Midwest Industries, Inc.
Secondary — a parts or tool maker, or a gunsmithing publisher

“Install M-Lok rails to the outside of the handguard, torque M-Lok screws to 15 in/lbs.”

 Free Float Hand Guard Installation Instructions — Midwest Industries, Inc., PDF p. 1, step 18 midwestindustriesinc.com [8]
Barrel nut (Midwest Industries SP Series barrel nut)
AR-15 with a Midwest Industries SP Series handguard		 20 ft-lb
27.1 N·m · 240 in-lb

Reported by Midwest Industries, Inc.
Secondary — a parts or tool maker, or a gunsmithing publisher

Grease the receiver threads; tighten with the MI wrench to 20 ft-lb 'or until the next gas tube hole aligns'. MI notes the SP nut spec is below the usual AR-15 barrel-nut value. Or until the next gas tube hole aligns with the upper receiver, as the maker says.

“Using the provided MI barrel nut wrench, tighten the barrel nut to 20 ft lbs or until the next gas tube hole aligns with the upper receiver.”

 Midwest Industries — SP Series Installation Instructions (AR15) — Midwest Industries, Inc., PDF p. 1, step 8 midwestindustriesinc.com [18]
Handguard screws (two-piece extended free-float M-LOK handguard)
AR-15 (delta-ring/standard barrel nut) with a Midwest Industries Two Piece Extended Free Float M-Lok Handguard		 25 in-lb
2.8 N·m · 2.1 ft-lb

Reported by Midwest Industries, Inc.
Secondary — a parts or tool maker, or a gunsmithing publisher

Align the handguard rail with the upper's rail before final torque.

“Align the rail on the upper and tighten the screws. Torque the screws to 25 inch lbs.”

 Midwest Industries — Two Piece Extended Free Float M-Lok Handguard Installation Instructions (AR15) — Midwest Industries, Inc., PDF p. 1, step 8 midwestindustriesinc.com [19]
Barrel nut (Daniel Defense Bolt-Up System barrel nut)
AR-15 (mil-spec flat-top upper) with a Daniel Defense MFR / MFR XL rail (same 55 ft/lbs in DD's DDM4 Rail, SLiM Rail 2019 Rev 1.0 and RIS II instructions)		 55 ft-lb
74.6 N·m · 660 in-lb

Reported by Daniel Defense, Inc.
Secondary — a parts or tool maker, or a gunsmithing publisher

Bolt-Up Plate first (counter-bored side to the muzzle), then the barrel nut; the plate stays loose after torquing. Install the low-profile gas block and tube before the rail.

“Tighten the Bolt-Up System Barrel Nut and torque to 55 ft/lbs using the supplied Daniel Defense Bolt-Up System Barrel Nut Wrench.”

 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., PDF p. 1, step 2 danieldefense.com [20]
Barrel nut (Daniel Defense Bolt-Up System barrel nut, MFR XS)
AR-15 with a Daniel Defense MFR XS rail		 50 ft-lb
67.8 N·m · 600 in-lb

Reported by Daniel Defense, Inc.
Secondary — a parts or tool maker, or a gunsmithing publisher

The Bolt-Up Plate remains loose after the nut is torqued.

“Tighten the Bolt-Up System Barrel Nut and torque to 50 ft/lbs using the supplied Daniel Defense Bolt-Up System Barrel Nut Wrench.”

 Daniel Defense MFR XS Rail — Installation Instructions (served from www.danieldefense.com) — Daniel Defense, Inc., PDF p. 1, step 2 danieldefense.com [21]
Rail screws (4) through the Bolt-Up Collar
AR-15 with a Daniel Defense MFR, MFR XL (M-LOK or KeyMod) or MFR XS rail		 25–28 in-lb
2.8–3.2 N·m · 2.1–2.3 ft-lb

Reported by Daniel Defense, Inc.
Secondary — a parts or tool maker, or a gunsmithing publisher

Insert all four screws from the receiver toward the muzzle and tighten in an alternating pattern; without a wrench, a quarter to half turn past first resistance.

“If you have an inch/pound torque wrench, the torque specification is 25-28 in/lbs.”

 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., PDF p. 1, step 5 danieldefense.com [20]
Rail screws (4) through the Bolt-Up Plate
AR-15 with a Daniel Defense DDM4 Rail or SLiM Rail		 32 in-lb
3.6 N·m · 2.7 ft-lb

Reported by Daniel Defense, Inc.
Secondary — a parts or tool maker, or a gunsmithing publisher

Tighten all four screws in an alternating pattern; without a wrench, a quarter to half turn past first resistance.

“If you have an inch/pound torque wrench, the torque specification is 32 in/lbs.”

 Daniel Defense DDM4 Rail — Installation Instructions, Rev 1.0 (served from www.danieldefense.com) — Daniel Defense, Inc., PDF p. 1, step 4 danieldefense.com [22]
RIS II rail screws (six) through the Bolt-Up Plate
AR-15 with a Daniel Defense RIS II rail		 29–32 in-lb
3.3–3.6 N·m · 2.4–2.7 ft-lb

Reported by Daniel Defense, Inc.
Secondary — a parts or tool maker, or a gunsmithing publisher

Centre screws first, then the bottom screws, then the top screws.

“tighten all six screws to 29-32 in/lbs using the supplied allen wrench in the following pattern: the center screws first, the bottom screws next, and the top screws last.”

 Daniel Defense RIS II — Installation Instructions (served from www.danieldefense.com) — Daniel Defense, Inc., PDF p. 3, step 3 danieldefense.com [23]
Barrel nut (BATTLEARMS WORKHORSE handguard)
Mil-spec AR-15 carbine with a BATTLEARMS WORKHORSE free-float M-LOK handguard w/ ASAL lock		 30–45 ft-lb
40.7–61 N·m · 360–540 in-lb

Reported by Battle Arms Development, Inc. (BAD / BATTLEARMS)
Secondary — a parts or tool maker, or a gunsmithing publisher

“Barrel Nut 30-45 ft-lbs”

 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), p. Installation Torque Recommendations battlearmsdevelopment.com [24]
Handguard screws (BATTLEARMS WORKHORSE)
Mil-spec AR-15 carbine with a BATTLEARMS WORKHORSE free-float M-LOK handguard w/ ASAL lock		 10–15 in-lb
1.1–1.7 N·m · 0.83–1.2 ft-lb

Reported by Battle Arms Development, Inc. (BAD / BATTLEARMS)
Secondary — a parts or tool maker, or a gunsmithing publisher

“Screws 10-15 in-lbs”

 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), p. Installation Torque Recommendations battlearmsdevelopment.com [24]
Barrel nut — final torque (BATTLEARMS RIGIDRAIL)
M16 / M4 / AR-15 with a BATTLEARMS RIGIDRAIL free-float handguard		 45 ft-lb
61 N·m · 540 in-lb

Reported by Battle Arms Development, Inc. (BAD / BATTLEARMS)
Secondary — a parts or tool maker, or a gunsmithing publisher

After the 40 ft-lb seating pass and loosening one-half turn; ceiling 50 ft-lb.

“Loosen the barrel nut one-half turn and re-torque to 45 ft-lbs. (Do not exceed 50 ft-lbs.”

 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), PDF p. 2, step 8 opticsplanet.com [25]
Rail retention clamp hex bolts (2) (BATTLEARMS RIGIDRAIL)
M16 / M4 / AR-15 with a BATTLEARMS RIGIDRAIL free-float handguard		 30 in-lb
3.4 N·m · 2.5 ft-lb

Reported by Battle Arms Development, Inc. (BAD / BATTLEARMS)
Secondary — a parts or tool maker, or a gunsmithing publisher

Alternate between the two bolts until both stop rotating at the set torque.

Threadlocker: Blue Loctite recommended on the hex bolts.

“Insert the rail retention clamp into the the RIGIDRAIL™ and tighten the hex bolts to 30 in-lbs.”

 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), PDF p. 3, step 13 opticsplanet.com [25]
Barrel nut (ODIN Works O2 Lite forend, into the forend adapter)
AR-15 with an ODIN Works O2 Lite M-LOK forend		 50 ft-lb
67.8 N·m · 600 in-lb

Reported by ODIN Works
Secondary — a parts or tool maker, or a gunsmithing publisher

Screw the forend adapter onto the receiver, align its gas-tube hole with the alignment pin, then torque the barrel nut into the adapter.

Threadlocker: Vibra-Tite on the barrel nut, per Vibra-Tite instructions.

“Torque the barrel nut to 50 ft. lbs.”

 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, p. Forend Installation Instructions odinworks.com [26]
Barrel nut (ODIN Works 223/5.56 forend barrel nut)
AR-15 with an ODIN Works 223/5.56 forend (installed with the 1 1/4" jumbo crowfoot)		 40–50 ft-lb
54.2–67.8 N·m · 480–600 in-lb

Reported by ODIN Works
Secondary — a parts or tool maker, or a gunsmithing publisher

“Use this crowfoot wrench to torque the barrel nut to 40-50 ft lbs”

 ODIN Works 1 1/4" Jumbo Crowfoot Wrench (for ODIN Works 223/5.56 Forend installation) — product page — ODIN Works, p. Features odinworks.com [27]
Muzzle device / suppressor mount (ODIN Works OSM 5, 1/2-28)
AR15 and variants with 1/2-28 muzzle threads, ODIN Works Suppressor Mount (OSM) 5		 35 ft-lb
47.5 N·m · 420 in-lb

Reported by ODIN Works
Secondary — a parts or tool maker, or a gunsmithing publisher

Hand-screw onto the barrel until snug, then torque; no shims or washers.

“Tighten down to 35 foot-pounds with a torque wrench”

 ODIN Works Suppressor Mount (OSM) 5 — product page, 'OSM Installation' — ODIN Works, p. OSM Installation odinworks.com [28]
Barrel nut (Faxon G3 Streamline handguard)
AR15 with a Faxon G3 Streamline Aluminum M-LOK handguard		 35–60 ft-lb
47.5–81.3 N·m · 420–720 in-lb

Reported by Faxon Firearms
Secondary — a parts or tool maker, or a gunsmithing publisher

1-3/16" wrench. Faxon: 'DO NOT OVER-TIGHTEN.'

“Torque barrel nut to industry specs using 1-3/16” wrench to at least 35ft/lbs but no more than 60ft/lbs.”

 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, p. Installation Instructions faxonfirearms.com [29]
Handguard locking-plate bolts (2) (Faxon G3 Streamline)
AR15 with a Faxon G3 Streamline Aluminum M-LOK handguard		 32 in-lb
3.6 N·m · 2.7 ft-lb

Reported by Faxon Firearms
Secondary — a parts or tool maker, or a gunsmithing publisher

Re-check that the bolts are tight after the first live-fire test.

“Install locking plate into the recess on the handguard and thread both bolts through the handguard and into the locking plate. Torque bolts to 32 in/lbs.”

 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, p. Installation Instructions faxonfirearms.com [29]
Muzzle brake (Faxon MuzzLok Gunner 3-Port 5.56, 1/2x28, MuzzLok timing nut — no crush washer)
5.56/.223 AR barrels threaded 1/2x28 with a Faxon MuzzLok Gunner 3-Port muzzle brake		 20–25 ft-lb
27.1–33.9 N·m · 240–300 in-lb

Reported by Faxon Firearms
Secondary — a parts or tool maker, or a gunsmithing publisher

Time with the MuzzLok extension nut; no crush washer or shims.

“Recommended torque: 20–25 ft-lbs”

 Faxon MuzzLok Gunner 3-Port 5.56 Muzzle Brake – Nitride | 1/2x28 — product page — Faxon Firearms, p. MuzzLok Timing System faxonfirearms.com [30]
Ambidextrous safety-selector lever screws (KAK ambi selector)
AR-15 lower built with the KAK Basic Ambi Build lower parts kit		 5–7 in-lb
0.56–0.79 N·m · 0.42–0.58 ft-lb

Reported by KAK Industry
Secondary — a parts or tool maker, or a gunsmithing publisher

De-grease the selector screw threads before assembly; KAK alternatively allows 'hand-tight'.

Threadlocker: Blue Loctite on the selector screws.

“De-grease ambi selector screw threads and apply blue loctite when assemblying, Tq selector screws to 5-7 in/lbs or hand-tight”

 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, p. Description kakindustry.com [31]
Barrel nut (AT3 Tactical handguard barrel nut)
AR15 with an AT3 Tactical SPEAR M-LOK handguard (identical step in the AT3 Pro Quad Rail instructions, INSTR-QR-01)		 30–60 ft-lb
40.7–81.3 N·m · 360–720 in-lb

Reported by AT3 Tactical
Secondary — a parts or tool maker, or a gunsmithing publisher

Reinstall gas block and tube after the nut is torqued.

“Install the barrel nut and apply 30-60 ft lbs of torque using the provided barrel nut wrench and a torque wrench.”

 AT3 Tactical SPEAR M-LOK Handguard — Installation Instructions (INSTR-SPEAR-03, Rev 3 Oct 18 2021) — AT3 Tactical, PDF p. 1, step 2 media.at3tactical.com [32]
Handguard socket-head screws (5/32 hex) (AT3 Tactical)
AR15 with an AT3 Tactical SPEAR M-LOK handguard or Pro Quad Rail		 40 in-lb
4.5 N·m · 3.3 ft-lb

Reported by AT3 Tactical
Secondary — a parts or tool maker, or a gunsmithing publisher

Insert from the left side; AT3's no-wrench alternative is 1/2 turn past hand tight. Then tighten the bottom set screws until they bottom on the barrel nut (no value).

“Torque to 40 inch-lbs, or 1/2 turn past hand tight.”

 AT3 Tactical SPEAR M-LOK Handguard — Installation Instructions (INSTR-SPEAR-03, Rev 3 Oct 18 2021) — AT3 Tactical, PDF p. 1, step 4 media.at3tactical.com [32]
Stock front QD screw (Magpul PRS GEN3 on a carbine receiver extension)
Mil-Spec AR15/M4 carbine receiver extension with a Magpul PRS GEN3 stock		 40 in-lb
4.5 N·m · 3.3 ft-lb

Reported by Magpul Industries Corp.
Secondary — a parts or tool maker, or a gunsmithing publisher

Front Body Screw only hand tight (1/8" hex).

“Torque front QD screw to 40 [in-lb] and front Body Screw until hand tight using 1/8” Hex Wrench.”

 Magpul MAG672 PRS GEN3 Stock — Installation Instructions (072-0115-A) — Magpul Industries Corp., PDF p. 1, Carbine Receiver Extension, st magpul.com [33]
Stock front QD screw (Magpul PRS GEN3 on a rifle receiver extension)
AR15 rifle-length receiver extension with a Magpul PRS GEN3 stock (rifle adapter cap)		 20 in-lb
2.3 N·m · 1.7 ft-lb

Reported by Magpul Industries Corp.
Secondary — a parts or tool maker, or a gunsmithing publisher

Front body screw hand tight.

“Torque front QD Screw to 20 [in-lb] and front body screw until hand tight using 1/8” Hex Wrench.”

 Magpul MAG672 PRS GEN3 Stock — Installation Instructions (072-0115-A) — Magpul Industries Corp., PDF p. 2, Rifle Receiver Extension, step magpul.com [33]
Stock rear body screws (2) when moving the QD footman's loop (Magpul PRS GEN3)
AR15 with a Magpul PRS GEN3 stock		 20 in-lb
2.3 N·m · 1.7 ft-lb

Reported by Magpul Industries Corp.
Secondary — a parts or tool maker, or a gunsmithing publisher

Over-tightening may impede the length-of-pull adjustment knob.

“Reinstall in desired location and tighten Screws to 20 [in-lb].”

 Magpul MAG672 PRS GEN3 Stock — Installation Instructions (072-0115-A) — Magpul Industries Corp., PDF p. 2, Reversible QD Footman's Loop magpul.com [33]
Receiver extension (Magpul UBR GEN2 buffer tube) into the lower receiver
AR15/M4 lower with a Magpul UBR GEN2 stock		 35–39 ft-lb
47.5–52.9 N·m · 420–468 in-lb

Reported by Magpul Industries Corp.
Secondary — a parts or tool maker, or a gunsmithing publisher

Hold the buffer retaining pin depressed while threading the tube in; use the square recess on the back of the tube with a 1/2" torque driver. Magpul cites US Army TM 9-1005-319-23&P for the value.

Threadlocker: None — 'DO NOT USE LOCTITE OR OTHER LOCKING COMPOUND ON RECEIVER EXTENSION THREADS.'

“tighten with a ½” torque driver and torque to 35-39 ft-lb.”

 Magpul UBR GEN2 Collapsible Stock — Installation & Usage Instructions for the AR15/M4 & SR25/M110 (072-0105-B) — Magpul Industries Corp., PDF p. 4 magpul.com [34]
UBR GEN2 Main Tube Nut
AR15/M4 with a Magpul UBR GEN2 stock		 20–25 ft-lb
27.1–33.9 N·m · 240–300 in-lb

Reported by Magpul Industries Corp.
Secondary — a parts or tool maker, or a gunsmithing publisher

Use the included adapter tool with an armorer's (castle-nut) wrench.

“tighten the Main Tube Nut to 20-25 ft-lb.”

 Magpul UBR GEN2 Collapsible Stock — Installation & Usage Instructions for the AR15/M4 & SR25/M110 (072-0105-B) — Magpul Industries Corp., PDF p. 5, step 7 magpul.com [34]

Function check

After every reassemblyPerform these checks on a verified-unloaded firearm. If any check fails, the firearm is not safe to fire — stop and see a licensed gunsmith.

Maintenance

Lubrication points

Cleaning notes

A direct-impingement AR runs better wet than dry. Carbon on the bolt tail and inside the carrier is normal and does not all need to be removed — focus on the locking lugs, the gas rings, the chamber, and the bore. Do not scrape carbon off the bolt tail with steel, which can remove material.

Suggested inspection interval: roughly every 1000 rounds. This is a general guideline, not a manufacturer specification.

Wear parts to inspect

Gas rings · Extractor and extractor spring insert · Bolt (inspect the cam pin hole and lugs for cracks) · Buffer spring · Ejector spring · Gas tube alignment

Common issues

SymptomLikely causeWhat to do
Firing pin retaining pin will not installCam pin missing or not rotated 90 degreesRemove the firing pin, install and rotate the cam pin, then reinstall. Never force the retaining pin.
Charging handle will not come outTrying to remove it before the bolt carrier groupRemove the carrier first, then pull the charging handle down and out.
Short-stroking or failure to lock back on an empty magazineWorn gas rings, gas leak at the gas block, undersized gas port, or a fouled gas keyCheck gas rings first, then gas block alignment and gas key staking. see a gunsmith
Bolt will not close fully into batteryFouled chamber, out-of-spec ammunition, or a dirty boltDo not force it with the forward assist on a round you suspect is out of spec. Clear the rifle and inspect the chamber.

Also covers

The procedures above are reported to apply to: M16A2/A4 · M4 Carbine · Most AR-15 pattern rifles from any manufacturer · AR-pattern pistols and SBRs. Verify against the manual for your specific model.

Similar manual of arms

Legal notes

Not legal adviceThe lower receiver is the serialized firearm in the United States. Barrel length, overall length, and stock configuration determine legal classification, and assembling certain combinations can create a regulated configuration. Verify the law where you are before changing any of those.

Sourcing

Confidence
high — Cross-checked against a primary source such as the manufacturer's manual or an issuing military technical manual.
Verification
Checked against an armorer/technical manual
Last updated
2026-10-29

References

Every source this page draws on, with its web address so you can read it yourself. Numbers in brackets elsewhere on the page point here.

Notes: Illustrated on 2026-09-14 with figures from TM 9-1005-249-23&P, the US Army maintenance manual for the M16 and M16A1. These are US Government works and therefore public domain, which is why they can be reproduced here. They depict the military rifles; the AR-15's fire control group differs, but the upper receiver, barrel, bolt carrier and bolt are the same parts in the same arrangement. The AR-15 platform spans hundreds of manufacturers. Piston-driven variants, side-charging uppers, and non-standard buffer systems deviate from this procedure — consult the manual for your specific rifle. Buffer removal: the TM note that the hammer must be cocked was added on 2026-10-03.

Found something wrong? Corrections are the most valuable contribution to this project. Open an issue with the model, the step, and a source.