Mk18 Mod 0 Clone
A Brief History of the Mk18
The Mk18 is a compact variant of the M4A1 carbine developed for U.S. special operations forces. Its roots trace back to the early 2000s when Naval Special Warfare Command (WARCOM) sought a shorter-barreled rifle optimized for close quarters battle (CQB), maritime operations, and vehicle use. The solution was a 10.3-inch barrel upper receiver mated to a standard M4 lower, creating a shorter, more maneuverable weapon without sacrificing reliability.
The earliest iteration, CQBR (Close Quarters Battle Receiver), was a drop-in upper developed by Crane Division, Naval Surface Warfare Center (NSWC Crane). By 2003, the platform included a paired lower and became known officially in military inventory as the Mk18 Mod 0.
The Original Specs
The part that makes the Mk18 Mod 0 is the upper receiver.
Like many new weapon systems, the Mk12 Mod 0 was born out of spare parts. With the evolution of the M16 and M4, the military had lots of M16A1 and M4A1 lowers lying around. These were repurposed when a new upper was configured. As such, many of the Mk18 Mod 0 lower receiver specs are consistent with those of the M4A1 carbine (typical) or M16A1 rifle.
The Mk18 Mod 0 was not complete without some standard accessories.
"Really Close" Clone Bill of Materials (~$2,150)
Unless you have access to a registered M16A1 machine gun lower, you will not be building a true Mk18 Mod 0 clone. Without an M16A1 machine gun lower receiver (manufactured by Colt or Hydramatic), the following components will not be clone accurate:
- Lower Receiver: Even if the lower has the correct profile and markings, it will not be drilled for auto sear pin. Colt makes great stuff for the U.S. Military. The stuff they release to the consumer market is NOT the same quality. Its not that they have a different spec for the consumer market…they just release the stuff that doesn’t pass the government standards. If you buy a Colt part, you are probably buying a 3rd or 4th round reject. When it comes to the lower, you can try to find a Colt M4A1 or M16A1 lower, but it is not worth the $800-900 you will pay for a stripped non-NFA lower (in our opinion). If you are a die hard clone fanatic, happy hunting. Our Mk18 clones are geared toward the rational enthusiast.
- Trigger Group: Without a select fire receiver, you will not be building with a full auto fire control group and auto sear. If you (legally) acquire a machine gun lower, you can absolutely build with a full auto trigger group and auto sear. Our Mk18 clones assume that you are working with a semi-auto setup.
- Safety Selector: Without a select fire trigger, there is no point of having a select fire safety selector, even if your trigger functions with one.
"Improved" Clone Bill of Materials (~$2,300)
Our “Improved” clone includes clone-appropriate upgrades to the following components:
- Bolt Carrier Group: We upgrade to our PBA Enhanced Phosphate BCG, which is built from Microbest components, is meticulously gauged to ensure efficiency, is built with Michiguns O.C.K.S., and includes Sprinco springs and rings (5-coil extractor spring, ejector spring, O-ring, and gas rings). The result is a super-efficient and robust BCG that will outperform the Mil-Spec Colt BCG.
- Trigger Group: We upgrade the Mil-Spec Colt trigger to a Geissele SSA-E. The 2-stage design and unparalleled quality results in far superior performance and feel. It is this reason that Geissele triggers (SSA, SSF, and SD-C) made their way into issued carbines. We chose the SSA-E for a lighter pull, though the SSA is more clone-appropriate for a combat carbine.
- Charging Handle: We move up to the PRI Gas Buster Big Military Latch charging handle, which was an upgrade on some issued mk18 Mod 0 guns. This charging handle is much better for suppressed shooters and the larger latch offers more confident engagement.
- H2 Buffer: The original spec called for an H1 buffer, but was often swapped out by armorers for an H2 buffer. This is more appropriate for the carbine length gas system (especially if shooting suppressed). The heavier mass contributes to a longer locked bolt time and better recoil management.
- Buffer Spring: Sprinco springs are superior to Mil-Spec buffer springs. The springs are chrome silicon wire stock, heat treated, stress relieved, dual stage shot-peened (post winding), and impregnated with a re-micronized molybdenum disulfide formulation. The result is a spring that will outperform and outlast (by far) your typical Mil-Spec spring.
"Close Enough" Clone Bill of Materials (~1,800)
Our “Close Enough” BOM is visually equivalent to the “Really Close” Mk18 Mod 0 clone, but includes less expensive but spec-equivalent (or better) components, where possible. Nobody will look at this gun and be able to tell that it is not spec-perfect without full disassembly and a keen eye. The following components deviate from the true specs:
- Trigger Group: We move to the ALG (manufactured by Geissele) Quality Mil Spec (QMS) trigger. In our opinion, this trigger is far superior to the issued Colt trigger, but doesn’t come with a premium price tag; win-win.
- Barrel: We move to the Ballistic Advantage 10.3″ Crane-spec barrel with a pinned FSB. This barrel is functionally equivalent to the Colt barrel, but comes in about $70 cheaper.
- Bolt Carrier Group: Despite the lower cost, our change to the BCG is a significant upgrade. We upgrade to our PBA Enhanced Phosphate BCG, which is built from Microbest components, is meticulously gauged to ensure efficiency, is built with Michiguns O.C.K.S., and includes Sprinco springs and rings (5-coil extractor spring, ejector spring, O-ring, and gas rings). The result is a super-efficient and robust BCG that will outperform the Mil-Spec Colt BCG.
- Charging Handle: We move from the overpriced Colt to a Brownell’s Mil-Spec. This is still a forged 7075-T6 charging handle, but comes in at less than half the price.
- Non-Colt Parts: We shift away from Colt branded parts to less-overpriced components for the receiver extension (still 7075-T6), castle nut, buffer, buffer spring, pistol grip, and LPK.
"Budget" Clone Bill of Materials (~$1,000)
Our “Budget” clone BOM shaves over $1,000 off the “Really Close” price tag. We won’t always throw together a budget version, because a budget clone will often look completely different. But for the Mk18 Mod 0, we can get you close enough that someone 15 feet away won’t be able to tell. We start with our “Close Enough” clone and swap out the following components:
- Upper Receiver: We shift from Colt to a BKF upper. Functionally, this is equivalent, but will lack the C mark. BKF makes superb low-cost components, so you are not sacrificing quality (in fact, you may find that BKF receivers have better fit and finish than the consumer grade Colt receivers). This swap saves you over $110.
- Handguard: We swap the KAC RAS for a Troy Industries quad rail drop-in handguard. Visually, these are hard to distinguish from a distance (especially once you add rail covers). The Troy handguard is an excellent alternative. This change saves us $125,
- Muzzle Device: We switch to a standard A2 birdcage flash hider. This saves about $100 without much of a functional change. If you are expecting to use this with the KAC QDSS-NT4 suppressor, this is not compatible and is the only functional difference.
- Rear Sight: The LMT sight is amazing. But it is also $250. That’s a lot to spend on a BUIS (back-up iron sight). For the budget build, we switch to a UTG fixed rear sight. This has the approximate look and has the same functionality as the LMT, but rings in about $200 cheaper.
- Lower Receiver: We move from the H&R M16A1 lower to a BKF M16A1 marked lower. Note that the profile of the lower is NOT technically M16A1 correct; only the markings are correct. The most obvious differences (i.e. visible from an assembled gun) are in the milling contours. The M16A1 differs from the M16A2 (and later) profile at the pivot pin lugs and the reinforcement of the buffer tube boss. It is worth noting that the milling contours were changed for a reason (increase strength); so going clone-accurate is more for bragging rights than for performance or durability. For a savings of over $70, these are subtleties that only a clone snob will scoff at. And out of all of the clone deviations in this build, this is probably not the one someone will linger on.
- Buttstock: We swap the LMT stock for a standard M4 buttstock. This change saves us about $150.
Accessories and Attachments
If you are building a clone and are taking the time to research the gun itself, you probably don’t want to throw random crap on it. If you want to stay clone-appropriate (i.e. what was issued in the battlefield), there are specific options to choose from. Note that you don’t need all of these to have a clone-appropriate build. The core accessories for the Mk18 Mod 0 include:
- Vertical Foregrip (required)
- Sling (required)
- Red Dot Sight and Mount (optional)
- Tactical Light (optional)
* Discontinued items (Aimpoint CompM2 and SureFire M951) can be purchased used on auction sites.
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