M16A4 clone build: the USMC rifle, part by part

The M16A4 is an M16A2 with a new top half. It kept the 20 inch barrel, fixed A2 stock and three round burst, and traded the fixed carry handle for a flat top with a detachable one.

The Marines picked it over the M4 in late 2002 and carried it through Iraq and Afghanistan until the M4 took over in 2016. Here's how you build one.

What an M16A4 clone copies

Your clone copies a general issue rifle: a 20 inch chrome lined barrel, rifle length gas, A2 furniture and a flat top. The early rifle wears a carry handle, the Iraq era Marine rifle an RCO and a KAC M5 rail.

An M16A4 with the KAC M5 RAS at a National Museum of the Marine Corps storage facility, Quantico, July 1, 2025. U.S. Marine Corps photo illustration by Sgt. James Stanfield, public domain, via Wikimedia Commons.

M16A4 specs at a glance

The barrel is 20 inches, government profile, 1 in 7 and chrome lined, with M4 feed ramps on production rifles. The selector reads SAFE, SEMI and BURST.

FN lists 39.63 inches and 8.79 pounds with a 30 round magazine. The Army manual says 9.87 pounds with a sling and loaded magazine.

M16A4 parts list: the issued part and what to buy

Here's every slot, what you'd buy and its in stock price on September 27, 2026. Exact is the issued part or its commercial twin, equivalent the same pattern from another maker, and budget looks right for less.

Product photography is supplied by the listed merchants through their affiliate feeds.

The lower receiver group

Every issued lower is a machine gun, so your clone turns civilian here.

Lower receiver: M16A4 marked, semi auto only

Small Arms Review says FN built most issued M16A4s and Colt built others. Every one is a post 1986 machine gun, so you'll use a semi auto lower with M16A4 style markings.

FN's and Aero's M16A4 lowers were out of stock when we checked, and PSA's was $79.99. All three are equivalents, not issued parts.

Trigger: a semi auto group in place of burst

The issued group has a burst cam, a machine gun part under federal law, so you'll use a mil spec semi auto trigger. MCRP 3-01A notes ambi selectors for left handed Marines, and CMMG's matches.

We won't recommend a forced reset trigger; see FRT legality by state. The CMMG and FN parts are equivalents, though FN's had no offers, and LBE's group is the budget pick.

Stock, buffer and grip: fixed A2 pattern

You need a fixed A2 stock with a trap door, a rifle receiver extension, buffer and spring, plus an A2 grip. Luth-AR sells the stock with its rifle buffer kit, or on its own. The Brownells stock and TacFire tube kit are the budget pair.

The upper receiver group

The top half makes it an A4.

Upper receiver: A4 flat top with M4 feed ramps

The issued upper is a flat top with M4 feed ramps, though owners say 1997 to 1999 uppers lacked them. FN's FN15 M16A4 upper is exact but was out of stock.

BCM's 20 inch upper group was in stock with a chrome lined barrel, F marked base, M4 feed ramps and an A2 flash hider, per BCM. It has no handguard or charging handle, and BCM's free bolt carrier was a limited time offer on its own site. BCM and LMT are equivalents, though LMT's listing doesn't state its feed ramps. Del-Ton and PSA are budget picks, and PSA's had no offers.

Barrel: 20 inch government profile, 1 in 7, chrome lined

FN and Colt made the issued barrels. The 1 in 7 twist was chosen for SS109/M855 ball and the long L110/M856 tracer, not heavy match bullets. Our M193 vs M855 vs M855A1 guide compares the loads, and our AR-15 barrel length guide covers the length.

FN's barrel, an equivalent, was out of stock and LMT's had no offers. Ballistic Advantage's budget barrel is in stock, but its listing doesn't say chrome lined.

Gas block: the F marked front sight base

The gas system is rifle length, with an A2 front sight base, bayonet lug, rifle gas tube and delta ring. Flat top barrels take the taller F marked base, which lifts the post for the carry handle and BUIS.

Muzzle device: the A2 flash suppressor

It's the A2 closed bottom flash suppressor, which the Army manual calls a compensator. A 20 inch barrel doesn't need it pinned. The Wilson and CMMG parts are A2 pattern, and KAK's is the budget pick.

Handguard: KAC M5 RAS and ribbed rail covers

The signature part is the Knight's Armament M5 RAS, KAC part 98065. It clamps to the barrel nut, isn't free floating, and needs rifle length gas, a delta ring and a fixed front sight base.

Nobody in our feeds had one, and KAC's own listing, at $346.61, was out of stock. KAC's 11 rib panel was out of stock too. Luth-AR's round A2 handguards suit the early rifle, the Midwest Industries rail is an equivalent, not a KAC copy, and Magpul's ladder covers are a budget stand in for the ribbed panels.

Bolt carrier group and charging handle

No source we found names the issued carrier's profile. Clone builders use M16 profile carriers sold for semi auto rifles. The handle is the standard M16A2 pattern, and MCRP 3-01A allowed an optional extended latch. Treat the Wilson and BCM carriers as equivalents; PSA's is the budget pick.

Iron sights and the Rifle Combat Optic

The sights changed over the years, so match yours to one.

PFC David Lindsay zeroes a newly mounted ACOG on his M16A4 aboard USS Essex, May 10, 2006. U.S. Marine Corps photo by Lance Cpl. Kamran Sadaghiani, public domain, via Wikimedia Commons.

Rear sight: the 6/3 detachable carry handle

The A4's handle carries the 6/3 sight, 300 to 600 meters in 100 meter steps, like the M4's. The A2's fixed 8/3 sight reads to 800.

Check the drum before you buy. Only the UTG listing in our feeds states 6/3, and owners warn that handles come in two heights. The LBE and Luth-AR handles are equivalents, and the UTG and NcStar handles are budget picks.

BUIS: Matech or KAC 600 meter flip up

Owners date Matech sights on new rifles to about late 2007 and USMC marked KAC 600 meter sights to late 2009, though usmcweaponry gives earlier dates.

We don't list the USMC marked KAC yet. KAC's commercial 600 meter micro sights are equivalents, since which KAC model the Marines fielded rests on owner reports. Matech's USGI listing had no offers, and its commercial flip up is an equivalent.

Optic: Trijicon TA31RCO-A4 on a TA51 mount

The Marine optic is the TA31RCO-A4, or AN/PVQ-31A, a 4x32 Trijicon ACOG. Its red chevron is calibrated for M855 from a 20 inch barrel, from 100 to 800 meters. MCRP 3-01A says the M4's AN/PVQ-31B can't be swapped onto an A4.

The commercial TA31RCO-A4CP includes the TA51 mount, and it was $1,331.50 at the one merchant with stock. Trijicon also sells the TA51 on its own.

Light, laser, foregrip, sling and bayonet

Once the M5 arrived, units hung lights, lasers and grips on it.

Light and laser: SureFire and PEQ stand ins

No manual we found names the issued light. Owners report SureFire M951, M952, M961 and M962 lights, then the M952V and M600 Scout.

MCRP 3-01A lists the AN/PEQ-15 and PEQ-16, both military items. The M600DF fits the later owner reports but was out of stock. The M640U and the laser are commercial stand ins, and our IR laser buyers guide covers your options.

Vertical foregrip and Grip Pod

MCRP 3-01A lists the vertical fore grip, or broomstick, and the Grip Pod. Owners call the Army's forward pistol grip a KAC part, which we don't carry. The Grip Pod LE was out of stock, the Daniel Defense grip is an equivalent and UTG's is the budget pick.

Sling, bayonet and magazines

The Army manual lists a web sling and MCRP 3-01A a three point sling, and owners remember Blue Force Gear Vickers slings from about 2006. Marines used the OKC-3S bayonet from 2003, the Army the M7 or M9.

We card the coyote Vickers, but no bayonet or GI web sling yet. The PMAG MOE is a budget stand in for the 30 round aluminum magazine.

M203 and the 37 mm flare launcher look alike

Some rifles in each squad carried the M203. A 40 mm launcher is a destructive device, so civilians use 37 mm flare launchers as look alikes, subject to state law. The Havoc below is a flare launcher, not an M203 copy.

Lance Cpl. Frederick P. Shearon shows Gambian soldiers his M16A4 with an M203 in Senegal, July 10, 2012. U.S. Marine Corps photo by Sgt. Tatum Vayavananda, public domain, via Wikimedia Commons.

M16A4 variants: USMC and Army rifles by era

Pick a year, then buy every part from it.

The early rifle: carry handle and round handguards

From 1997, rifles came with round A2 handguards and a carry handle, and owners report A2 barrel assemblies with non F bases on the first ones. Colt's AR15A4 is close, and our Black Hawk Down CAR-15 build covers an older carry handle rifle.

The 2004 Fallujah rifle

A Marine photo from Fallujah on November 26, 2004 shows a fixed A2 stock, an ACOG and a railed handguard. Owners report TA01NSN and TA31F ACOGs before the RCO, and by 2005 carry handles stowed and many rifles without a BUIS.

Later Marine rifles: RCO, BUIS and PEQ laser

Most people mean this rifle when they say USMC M16A4 clone. MCRP 3-01A, from 2012, lists the RCO on a TA51, a BUIS behind it, a vertical grip or Grip Pod, a three point or web sling, and an AN/PEQ-15 or PEQ-16.

The Army M16A4 with an M150 or M68

PEO Soldier lists the M150 RCO, Trijicon's TA31RCO-M150CP, for the M16A4, and owners report Aimpoint M68 red dots on many Army rifles. The CompM4 is an equivalent. For 20 inch marksman rifles, see the SAM-R clone build and SDM-R clone build.

How to build an M16A4 clone: factory rifles and uppers

You don't have to start from a stripped lower. FN, Colt and PSA sell M16A4 style rifles, all commercial equivalents.

FN 15 Military Collector M16

FN lists a 20 inch, 1 in 7, button broached, chrome lined barrel, the KAC M5 RAS with covers, a fixed A2 stock and an ambi selector. It was $1,774.89 when we checked, the only in stock way we found to get a real M5.

Colt AR15A4

Colt's AR15A4 is the carry handle rifle, with A2 handguards and no rail. It was $1,175.99 to $1,191.68 at the two dealers with stock when we checked. Colt's CR6700A4 listing, another 20 inch carry handle rifle, was out of stock.

PSA M16A4 and other 20 inch complete uppers

PSA's "M16A4" upper and rifle use a quad rail, not a KAC M5, and the rifle's name says the barrel is nitrided. Neither had a live offer when we checked, and neither did Brownells' BRN-16A4 20 inch upper.

What an M16A4 clone costs today

The iron sight rifle came to $1,120.25, from the table's rifle parts and carry handle plus Luth-AR's $19.49 A2 handguards. The RCO rifle drops the handle and handguards for the optic, BUIS, vertical grip and a $178.95 Midwest Industries rail, for $2,740.20. Neither includes the small lower parts you'll still need.

BCM's own site listed that upper out of stock the same day, so check before you order.

What you can buy today and what is unobtainable

Stock is the real limit, and some parts can't be sold to you at all.

Out of stock when we checked

On September 27, 2026 we found no in stock offer for the KAC M5 or its panels, FN's barrel, lower and upper, or Aero's lower. LMT's barrel, BCM's F marked base, the Matech USGI BUIS, the Grip Pod LE, the M600DF and Colt's CR6700A4 were out too.

Parts no retailer can sell you

The issued select fire lower and burst group are post 1986 machine gun parts, the AN/PEQ lasers are military items and the M203 is a destructive device. The old SureFire lights aren't restricted, but no feed we track lists them.

The civilian legal path to an M16A4 clone

The 20 inch barrel makes this an easy clone to build legally. Only the fire control changes.

The NFA: why no issued M16A4 is transferable

Burst fire makes the issued rifle a machine gun under the NFA. You can only own a machine gun registered before May 19, 1986, and issued M16A4 lowers postdate that, so none can be transferred to you. A burst capable look alike would need a pre 1986 registered receiver.

A 20 inch barrel needs no SBR paperwork

A barrel under 16 inches means short barreled rifle paperwork unless a pinned and welded muzzle device brings it to 16. Your 20 inch barrel needs neither, and no suppressor was in the issued kit. If you add one, our suppressor guide covers the paperwork.

State limits on bayonet lugs, flash hiders and magazines

Some states restrict the bayonet lug, the flash suppressor and 30 round magazines, so check yours. The lower and any complete rifle ship to a licensed dealer.

M16A4 history: from the M16A2 to the M4 switch

The M16A4 replaced the M16A2 on July 29, 1997, after testing as the M16A2E4. Our M16A1 clone build covers the Vietnam era rifle.

Why the Marines chose it over the M4 in 2002

In late 2002 the Marines chose the M16A4 over the M4, citing reliability. Wikipedia describes a 2002 Marine test in which the M4 failed 186 times in 69,000 rounds to the M16A4's 61. Small Arms Review reports Marine orders to FN for 4,264 and then 27,000 rifles, unconfirmed elsewhere.

Iraq and Afghanistan with the Marines

The rifle carried Marine infantry through Fallujah in 2004, the Anbar years and Helmand from 2008. Trijicon dates the RCO's selection to 2004 and 2005.

Replaced by the M4 in 2015 and 2016

Length was the complaint: a fixed stock, body armor and a short eye relief optic made it awkward in vehicles and buildings. On October 26, 2015, Marine Corps Times reported that Gen. Robert Neller had approved the M4 for infantry, with the swap due by the end of September 2016.

The A4 moved to support and non infantry Marines. A 2026 caption lists M16A4s at a range in Sweden, but every stock pictured is collapsible, so we treat it as disputed.

M16A4 vs M16A2, M16A3 and M4

The M4 took the A4's job with a shorter barrel and an adjustable stock. The two share the 6/3 carry handle but not the RCO. For a carbine of the same years, see our M4A1 Block I clone build and M4A1 Block II clone build.

How the A4 differs from the A2 and A3

The A2 has a fixed carry handle with the 8/3 sight. The A4 moved to a flat top and a detachable 6/3 handle and kept burst. The A3 fires SAFE, SEMI and AUTO, and the Army manual describes it with rails, though Wikipedia says the original looked like an A2.

The M16A5 that never existed

M16A5 was never an official designation. RECOIL and Everyday Marksman describe a proposed A4 update with an adjustable stock, and RECOIL says it lost out to the M4 and the M27.

M16A4 builds on GPP: what they show

Of every GunPartPicker cart saved from December 10, 2025 to September 27, 2026, one is named M16A4: a BCM 20 inch upper and KAC M5 on a PSA M16A2 lower.

A wider net finds 52 carts with an M16A4 marked lower, an M16A4 upper or the M5, created December 13, 2025 to September 17, 2026. Of the 46 with more than one part, 27 hold a barrel or upper of 16 inches or shorter, and only 5 pair a 20 inch barrel or upper with the M5 or a carry handle.

Aero's M16A4 lower is in 25 of those 52 carts from December 2025 to September 2026, so people mostly want the roll mark on a carbine. See barrel length trends in GPP builds.

What the internet gets wrong about the M16A4

Most M16A4 myths come down to a sight, a maker or a caption.

Semi and three round burst, never full auto

The M16A4 fires SAFE, SEMI and three round BURST, per the Army manual, FN and MCRP 3-01A. The M16A3 is the full auto one.

The RCO chevron reads to 800 meters, not 600

Trijicon and MCRP 3-01A put the RCO's drop compensation at 100 to 800 meters. The 600 meter figure belongs to the carry handle and BUIS, and not every TA31 is an RCO.

FN M16A4 or Colt M16A4: who built them

Both. Small Arms Review says FN built most and Colt delivered just over 32,000 rifles in 2001, and Defense Industry Daily lists December 2007 orders to both.

The BUIS does not work with the RCO mounted

MCRP 3-01A puts the BUIS behind the RCO and says the RCO must come off before you use it. You won't get a co witness.

Sources and photo credits