Mk18 Mod 0 Clone Build Guide: The Original CQB Weapon System

On 28 January 2006, a boarding team sailor on USS Carter Hall drew a short carbine at a weapons issue in the Indian Ocean. The Navy caption called it an MK-18. The panel engraved on its magazine well read MK18 MOD0 CARBINE, beside an anchor.

That's the rifle you're cloning. Much of what's written about it, our first version included, fails a check against the records. So we rebuilt it from Crane's contract notices, federal stock records, Christopher R. Bartocci's April 2008 Small Arms Review article (SAR below) and dated Navy photos.

What is the Mk18 Mod 0?

The Mk18 Mod 0 is the Navy's designation for a complete 5.56mm carbine built around the Close Quarters Battle Receiver (CQBR), a short upper from Naval Surface Warfare Center Crane in Indiana. Naval Special Warfare wanted something as handy as a submachine gun for boarding ships that still fired rifle ammunition and took M4A1 rails, optics and lasers.

The upper got its stock number on 18 June 2002, as an M4A1 upper with a 10 inch barrel assembly for SPECWAR use only. The complete carbine, CARBINE 5.56MM MK18 MOD0, followed on 25 January 2005.

How Crane built it from surplus M16A1 rifles

SAR says Crane's hosts were obsolete Navy M16A1s. Crane converted their lowers, kept each rifle's bolt carrier group and cut Colt 14.5 inch M4 barrels down, with LMT's Karl Lewis helping develop the barrel.

In May 2004 Crane announced its intent to award Colt a sole source contract for up to 2,000 carbines and 5,000 CQBR receivers. We never found the award, but SAR confirms Colt delivered both, with its carbines on new M4A1 lowers. The same A1 conversion is reported on the Mk12 Mod 0, another Crane rifle on M16A1 lowers.

The Mk18 vs CQBR: clearing up the confusion

People use the names interchangeably. The records don't.

CQBR is the upper, Mk18 Mod 0 the whole carbine

The CQBR came first, with a 2002 stock record for an upper receiver. Crane's 2004 notice still asked for an "M4A1 Carbine with CQBR Upper Receiver," and GlobalSecurity says the CQB component left SOPMOD in 2003 to become the Mk 18. The 10.3 inch upper you build is a CQBR. The finished rifle is the Mk18 Mod 0.

Navy SEALs secure a mock U.S. Embassy during the Desert Rescue XI exercise at Naval Air Station Fallon, Nevada, on 7 August 2003, before the Mk18 Mod 0 had its own stock number. Both short carbines wear Knight's Armament quad rails over front sight bases, and the left one has a red blank firing adaptor. A 2006 AR15.COM post identifies them as Colt uppers with KAC RIS handguards. Photo: U.S. Air Force, Staff Sgt. Aaron D. Allmon II (VIRIN 030807-F-7823A-019), public domain, via Wikimedia Commons.

Mod 0 or CQBR Block I: the clone community split

Block I and Block II are SOPMOD accessory kits, not rifle names. One enthusiast parts list calls an A1 lower with a KAC RIS a Mod 0, and an A2 or UID lower with a KAC RAS a CQBR Block I, citing no sources. Even "Mk18 Mod 1" appears in no primary document we found.

You'll build to that list's split, so we use it too, and our CQBR Block I clone build draws the same line.

Why 10.3 inches?

The common explanation has no source.

Shortest length that still took the KAC suppressor

SAR says 10.3 inches was the shortest barrel that still let Crane fit Knight's Armament's quick detach suppressor. The KAC can in the Block I kit was the QDSS-NT4. It's one source, and we found no second.

Our first version said 10.3 was the shortest barrel that would reliably cycle carbine gas. We can't find a source for that, or for the length trials it described.

10.5 inches first, then 10.3

SAR reports that Crane first cut the barrels to 10.5 inches before moving to 10.3, and that LMT made some 10.5 inch barrels. M4Carbine.net posters and Charlie's Custom Clones say Crane cut straight to 10.3. If you want the earliest look, the LMT 10.5 inch barrel below matches SAR's LMT variant.

Who carried the Mk18

SAR lists SEALs, fleet boarding teams, Navy EOD, boat security and search and rescue units. It says the rifle may be seen with Rangers, Special Forces and Delta, but no document we found names those units.

Naval Special Warfare, VBSS and EOD crews

The best fleet evidence is Navy photography. In January 2006 a Navy photographer caught a USS Carter Hall boarding team sailor drawing an MK-18, then the crew qualifying with them in the Persian Gulf.

Crew members of the dock landing ship USS Carter Hall (LSD 50) fire MK-18 rifles during a live fire weapons qualification in the Persian Gulf, 9 February 2006. Quad rails, vertical grips and red dot sights are visible. Photo: U.S. Navy, Photographer's Mate 2nd Class Michael J. Sandberg, public domain, via Wikimedia Commons.

How to spot a Mod 0 in Navy photos

Look for a front sight base on the short barrel, a KAC quad rail and a SOPMOD pattern stock. Clone threads read odd numbered rail slots as a RIS and even numbered ones as a RAS.

Some lowers carry an engraved MK18 MOD0 CARBINE panel with an anchor on the right of the magazine well, as in this January 2006 Carter Hall photo. Don't count on it. A 2006 poster who zeroed hundreds of Mk18s saw none marked.

The visit, board, search and seizure team of the destroyer USS Bulkeley (DDG 84) practices gun handling with the MK-18 in the Mediterranean Sea, 19 June 2008. The carbines show front sight bases, quad rails and Aimpoint type red dots, and no suppressors. Photo: U.S. Navy, Mass Communication Specialist 3rd Class David Wyscaver, public domain, via Wikimedia Commons.

The complete parts list

Here's the full Mk18 Mod 0 parts list: the issued part, how well it's documented and what we stock. We cross checked every slot against that enthusiast parts list, and where it disagrees with the records, we go with the records.

The Mk18 Mod 0 clone parts we stock, laid out overhead. Product photography is supplied by the listed merchants through their affiliate feeds.

Evidence runs from strong (contract notices, stock records, or SAR plus a second source) to weak (forums or enthusiast lists).

The lower receiver group

Only the stock here has a real paper trail.

Lower receiver: M16A1 profile with the Mk18 engraving

Crane used converted M16A1 lowers, and Colt's carbines came on new M4A1 lowers, so either is right. No source we read ties the GM Hydramatic lowers clone sites name to the Mk18, and H&R turns up only on a Mk12 Mod 1.

The issued lower is select fire, so you need a semi auto one. H&R's retro M16A1 lower is our equivalent, without the Mk18 engraving, and PSA's A2 pattern lower is a budget lookalike, not an A1. We don't stock an engraved replica. For the host rifle, see our M16A1 clone build.

Trigger, trigger guard and grip: GI or Geissele SSA

The issued fire control was the host lower's SAFE, SEMI, AUTO set, and one owner reports Geissele SSF select fire triggers in SOCOM Mod 0s by 2014. You can't use either. The enthusiast list gives Colt or Geissele's semi auto SSA and SSA-E, so Geissele's SSA is here as the equivalent, plus a budget mil spec kit if you want the GI look.

The A2 grip and GI trigger guard come from enthusiast lists only, and the A2 grip card is a pattern match.

Stock: LMT SOPMOD, the L7LA2B Crane bought

On 12 December 2005 Crane posted a sole source buy of LMT's cheekweld buttstock, P/N L7LA2B. SAR says the Crane conversions used it, and the carbine's stock record lists a sloping cheekweld buttstock.

LMT's L7LA2BA in black, or L7LA2BAT in tan, is your exact part today, and B5's Government Issue SOPMOD is the budget pick. Our first version said B5 wasn't military issue, but Wikipedia's SOPMOD list names both makers.

Receiver extension, buffer and one point sling plate

SAR says Crane used a six position carbine receiver extension. Nobody documents the buffer, so any weight you read, Wikipedia's uncited H and H2 included, is your call. Our tube and buffer cards are pattern matches, and the Luth-AR assembly is the budget route.

SAR also says the end plate became a one point sling adapter. Clone lists call it a CQD, and one forum poster names Dieter, but we don't stock a Dieter mount, so the single point end plate here is an equivalent.

The upper receiver group

The upper is the best documented half, and most of it is still sold.

Upper receiver: Colt M4 flat top

Crane's 2004 notice named Colt as sole source, and SAR says Colt made the complete uppers. Forge mark details are forum readings.

Colt's M4 upper assembly is exact, but it was out of stock on 27 September 2026. LMT's upper is the in stock equivalent, though LMT uppers on the Mk18 are only a forum claim. Wilson Combat's forged upper is the budget pick.

Barrel, gas block and front sight: Colt 10.3 inch

SAR describes a Colt barrel with a light M4 contour, a chrome lined bore and chamber and a 1 in 7 twist, built to the GI M4 spec. It runs carbine gas through an F marked front sight base. Crane reworked the port, but nobody documents its size.

Colt's M4CQB 10.3 inch assembly is your exact pick, though a match to the military port, lug and markings is unconfirmed. LMT's 10.5 inch matches SAR's LMT variant. A bare barrel needs an F marked base and a post, and the nitrided Rosco 10.5 is the budget barrel.

Muzzle device: KAC M4QD, the NT4 flash hider

Clone lists call it the NT4 flash hider. KAC sells it as the M4QD Flash Hider Kit, P/N 93048, the mount for its QDSS-NT4, and the government NT4 kit record lists the same part. It's the exact part.

A poster signing CD says the 2005 and 2008 repair standards show an A2 birdcage, the budget card here. A fleet boarding team veteran says their rifles had no NT4s.

Handguard: KAC M4 RIS vs RAS, and how each mounts

Neither KAC rail free floats. KAC says its M4 RAS, P/N 98064, locks to the standard barrel nut with a clamp and screw and needs the delta ring, front sight base and round handguard cap. Forum members describe the older RIS clamping at the front cap instead.

Both went on Mod 0s. SAR says Crane fitted the RIS and pictures Colt configured uppers with the RAS, and a 2006 photo analysis on AR15.COM found the RIS. The rail NSN clone sites quote predates KAC's first RAS sale, and sources disagree on which rail it covers.

The RIS is out of production and gone from KAC's catalog. Our RAS card is the Colt configuration, not Crane's RIS, and it was out of stock on 27 September. The UTG drop in rail is a budget lookalike.

Bolt carrier group and charging handle

SAR says Crane kept each host's M16A1 carrier and Colt uppers got Colt bolts, all with the gold heavy extractor spring, black insert and O-ring. An M16 profile carrier is your pick, and it isn't an NFA item. The Colt carrier is exact but was out of stock, so BCM's is the in stock equivalent and Phase 5's the budget one.

The charging handle is disputed. CD reads the repair standards as a GI handle, while Split66 on M4Carbine.net and a 2019 reply say PRI's M84 Gas Buster. We default to GI and card the Gas Buster too.

Rear sight: LMT L8A fixed, not a KAC flip up

Crane bought LMT L8A fixed rear sights sole source in April 2004 and again in April 2005, the second time as "Rear Sight for CQBR Upper Receiver." SAR calls it standard. A 2006 poster says his older photos show KAC's 300 meter Block I sight instead.

We don't stock the L8A and couldn't confirm LMT still sells it. SAR says the Matech sight was also used, so the Matech card is a documented alternative. It ties A.R.M.S. #40 sights to EOD rifles, but none was in stock on 27 September. The out of stock KAC 300 meter fits earlier rifles. If you want the fixed look, Daniel Defense's A1.5 is the closest stand in, and Samson's is the budget pick.

Mk18 Mod 0 optic, laser, light and suppressor

These came from SOPMOD Block I, which our M4A1 guide covers as the SOPMOD Block I kit on the M4A1. The enthusiast list gives light, laser and suppressor as None, but all three were Block I items.

Optic: Aimpoint CompM2 in a Wilcox mount, or an ACOG

SAR says optics weren't standard and names the ACOG and the M68, the Army's name for the CompM2, as most common. The Navy's ECOS-N is a CompM2 in a Wilcox mount, and period photos show Aimpoint type dots, so that's your clone pick.

No new CompM2 shows up in our feeds. TNVC's ECOS-N reproduction kit puts an Aimpoint PRO in a Wilcox mount, the closest card here, but it was out of stock on 27 September. The CompM4, sold as the Army M68 CCO, is our in stock equivalent: a 30mm tube like the CompM2, in an AD-68H mount that isn't a Wilcox. If you're building an ACOG rifle, a TA01 4x32 in flat dark earth is a close match rather than a documented issued model. The Aimpoint PRO is the budget dot.

Suppressor: KAC QDSS-NT4

The NT4 is KAC P/N 96062-1, NSN 1005-01-437-0324, recorded in 1996 as a kit that includes the 93048 mount. Wikipedia's SOPMOD list puts two in every Block I kit, though the boarding team veteran says fleet rifles went without. KAC still lists it in black and flat dark earth, and we card the black one, though both were out of stock on 27 September. The newer NT4 PRG is in stock, but it isn't the issued can, and we couldn't confirm it fits the M4QD hider.

Laser and light: AN/PEQ-2 and the Insight VLI

Wikipedia's SOPMOD list puts two AN/PEQ-2 IR pointer illuminators and two Insight Visible Light Illuminators in each Block I kit, plus one AN/PEQ-5 visible laser. The LA-5C/PEQ, a high power PEQ-15 variant, and the M3X came later with SOPMOD Block II accessories.

The issued lasers are military only, but civilian legal IR lasers exist. Your DBAL-A3 card is an equivalent in a PEQ-15 style housing, and the SureFire Scout is a modern stand in for the VLI.

Foregrip and front sling mount: KAC and CQD

The KAC vertical grip was a Block I item, and EOD rifles often wore a GripPod instead. The front sling mount is a CQD on enthusiast lists, maker unconfirmed, and no sling is documented for the Mod 0. SAR calls Mk 262 Mod 1, a 77 grain open tip match load, SOCOM's choice for this rifle.

KAC's forward grip is the exact card, but it was out of stock on 27 September, so the generic grip is your budget pick. The Grip Pod GPS-02 is an equivalent for EOD rifles, since we couldn't confirm it's the issued GP502. We still don't stock a CQD mount. A single point bungee suits the one point plate: Blue Force Gear's UDC is the equivalent and AIM Sports' the budget pick.

Colt's USGI aluminum magazine is the pattern match. Brownells, DuraMag and D&H aluminum mags are equivalents, and the polymer PMAG is the budget pick. A 77 grain load is the ammunition equivalent, and Sig's is the cheaper one.

Mk18 Mod 0 variants over its service life

What a Mod 0 wore depended on who built it and who carried it.

The Mod 1 and its Daniel Defense RIS II rail

The next Mk18 moved to Daniel Defense's RIS II. The stock number Wikipedia gives for that rail was assigned on 9 February 2007, and a clone thread called it the Mod 1 rail by 1 January 2009. That rifle is the CQBR Block II with the Daniel Defense RIS II. For what followed, see the later M4A1 URGI upper.

What the internet gets wrong about the Mk18 Mod 0

Most of these trace to uncited Wikipedia lines and retailer pages. A few were ours.

The Mk18 name came after the CQBR, not before

Our old subtitle had the order backwards: the CQBR upper was recorded in 2002, the Mk18 Mod 0 carbine in 2005. Wikipedia's infobox also names Colt and Daniel Defense as designers, with a 1999 date cited to SAR, but SAR credits Crane and gives no year.

Neither KAC rail is a free float rail

Our first version had the RIS free floating and the RAS clamping the delta ring, yet KAC and The Full 9 say neither free floats. Grey Dynamics' RAS answer fits Colt supplied rifles only, and Charlie's Custom Clones' dated rail windows cite nothing.

Numbers with no source: the 0.070 port and 10,000 built

The 0.070 inch gas port comes from Wikipedia, an enthusiast parts list and Charlie's Custom Clones, uncited, and they disagree on when. SAR says only that the port was modified. Wet Worx and Wikipedia say more than 10,000 were built, also uncited, while Crane's 2004 solicitation capped orders at 2,000 carbines.

What our earlier version of this guide got wrong

The first version went live in September 2026. Here's what we corrected.

What you can buy today and what is unobtainable

On 27 September 2026, the closest in stock card in each lower and upper slot above, iron sights included, came to $1,514. That leaves out a handguard, since the KAC RAS was out of stock, plus a lower parts kit, optics, laser and light. The cards show today's prices.

Exact Mod 0 parts still sold new

The LMT SOPMOD stock, KAC M4QD and Colt M4CQB barrel were in stock that day. KAC still lists the M4 RAS and the NT4, but both were out of stock.

Secondhand only: KAC RIS, CompM2 and Wilcox mount

The RIS is out of production, and no new CompM2 or standalone Wilcox Aimpoint mount appears in our feeds, so you'll be shopping secondhand.

Parts no retailer can sell you

Select fire lowers and auto fire control parts are machine guns, off limits unless you buy a transferable one registered before 1986, and we don't card the Geissele SSF. The AN/PEQ-2, PEQ-5 and military Mk 262 lots aren't sold to civilians.

Mk18 builds on GPP: what they show

We looked for Mod 0 builds in our own data and found none. Searching saved build names for Mk18, Mark 18, CQBR or close quarters battle turned up seven, created 21 January to 29 June 2026, and three of them pass our filter of a lower, upper, barrel and five or more slots. None is flagged as a bot, though two predate our bot check.

Seven builds named Mk18, none of them a Mod 0

None holds a KAC rail, an M16A1 style lower, a Colt 10.3 inch barrel, an LMT SOPMOD stock, an Aimpoint or an ACOG. Across those seven builds, saved 21 January to 29 June 2026, three run 10.3 inch barrels, two run 11.5 and one runs 18, and EOTech took three of the four optic picks. They're Mod 1 or modern builds.

In the 90 days to 27 September 2026, 114 searches on our site contained Mk18, and 39 named Daniel Defense. Nobody has searched "mk18 mod 0" since our search log began on 23 April 2026. Period parts do get added, just not to Mk18 builds. Adds to any GPP build, 31 January to 27 September 2026:

The bot filter covers adds from 22 April onward.

Should you build a Mk18 Mod 0 clone?

Build one if you want the rifle Crane made, and expect the defining parts to be the hardest to buy.

Clone correct means hunting secondhand KAC parts

A clone correct Mod 0 needs a KAC RIS, an LMT L8A, a CompM2 in a Wilcox mount and a KAC vertical grip, and none of them was in stock on GPP on 27 September. A near clone uses the KAC RAS that Colt's own rifles wore, plus parts sold new: the LMT SOPMOD, KAC M4QD, Colt 10.3 inch barrel and an H&R A1 lower.

When a CQBR Block II makes more sense

If you want a modern short Mk18, you're in good company: all seven builds named Mk18 on GPP, saved 21 January to 29 June 2026, are Mod 1 or modern style. Build the CQBR Block II with the Daniel Defense RIS II. For the same idea without the history, see the Sicario task force build or the Act of Valor carbine.

The civilian legal path to a Mk18 Mod 0 clone

Your clone will be semi automatic, because the issued rifle is a machine gun.

The SBR question

A 10.3 inch barrel with a stock is a short barreled rifle under the NFA. Since October 9, 2026, ATF no longer enforces Form 1 or Form 4 registration for SBRs, so federally you can assemble it today. Filing a Form 1 is optional and costs $0. A Form 1 has always meant engraving your own maker markings, and a clone Mk18 engraving doesn't replace them. ATF has stopped enforcing the NFA marking rule for SBRs, but it hasn't said whether that covers a voluntary filing. Some states ban SBRs outright.

Pistol or pinned to 16 inches: the alternatives

Pistol and brace rules have changed federal status more than once, so check them before you rely on one. Otherwise you need a permanently attached device about 5.7 inches long, like a pinned and welded dummy can, to reach 16 inches. It changes the look, and it's rarely done.

Suppressors, state bans and crossing state lines

An NT4 or any other can is an NFA item, but since October 9, 2026 a Form 4 is optional, and some states ban them. You'll still need ATF approval on Form 5320.20 before taking an SBR across state lines. Our guide to what changed for NFA paperwork in 2026 covers the current process.

Sources and photo credits

Every claim above traces to one of these.

Sources

Photo credits