CLONING THE M4 CARBINE AND ITS VARIANTS
A hundred ways to replicate a mil-spec M4 carbine from scratch
In recent years, replicating service rifles has become one of the hottest trends for both military collectors and firearms enthusiasts alike. Some wish to recreate the weapon that they were issued while serving in the military while others simply want to clone a favorite rifle variation that they’ve seen used by our nation’s armed forces. Regardless of the reason, choosing which rifle to replicate is the first step.
Fans of the AR-15 platform have more than a few choices as far as which direction to go. Being America’s frontline weapon for going on five decades, the Ar-type rifle has been modified by the military every which way to serve a variety of purposes. From the lengthened and accurized Navy Mk12 to the compact and agile CQBR, each different type of Ar-style weapon has a fascinating history.
One of the most widely used carbines in the U.S. military is the M4. Developed over years but finally officially adopted by the U.S. military in 1994, the M4 is essentially a shortened version of the M16. Treading the middle ground between the performance of a longer rifle and the agile compactness of a close-quarters battle sub gun, the M4, with its 14.5-inch barrel and collapsible stock, became the do-all carbine of choice. Since it first went into service, the M4 itself has itself given birth to many a variant.
Before we delve any deeper, let us clarify that when we use the term “clone,” what we mean is to replicate, within reason, the details, attachments, accessories and components of a service weapon that was used by the military at a particular point in time. Just how accurate you want to get is up to your budget and parts procurement skills.
Some clone builders are sticklers for the fine details, and to them we tip our hats. We, on the other hand, are more forgiving and will make do with what we can get that’s within
our budget and capability. However, there’s a certain satisfaction about getting the details just right or lucking out and finding an old out-of-production part to complete your build.
M4 and Variants
The M4 is chambered to accept 5.56x45mm NATO caliber rounds and features a 14.5-inch barrel with a 1/7 twist rate. The most common round it employs is the 62-grain M855. Originally developed and manufactured by Colt for the military, it is has a collapsible buttstock and its most basic versions feature a flat-top, Picatinny-railed receiver and a detachable carry handle as well as a plastic handguard. Nearly a decade into the 2000s, the U.S. Army finally took over ownership of the design and embraced other companies such as FN Herstal to supply the M4 as well. The M4 features a semi-auto firing mechanism that can also be switched to fire threeround bursts. An M4A1 variant has also been used since 1994, initially mainly with special operation units. Instead of a three-round burst option, it has a full-auto-capable trigger. Other differences over the original M4 compared to an updated M4A1 include a heavier profile barrel and a heavier H2 buffer. Other M4 variants exist, but for the purpose of this article, we’ll focus on these two.
Accessories found on an M4 may vary widely and depend on factors such as the time period in which it was issued, the military branch and unit it was issued by, and the individual end user’s personal setup. For these reasons, M4s can differ from one another, even those issued at the same time and in the same unit. That said, M4 clones and their accessories would naturally differ as well. That fact might drive some purists nuts, but for others, it’s this leeway that makes building an M4 more engaging. Being able to set up an M4 how you want it within the confines of what was issued is an interesting prospect.
U.S. Special Operations Command added more M4 variants when they developed an enhanced kit for use with Special Forces units. Commonly called SOPMOD, which stands for Special Operations Peculiar Modification, the kit is based on an M4A1 carbine and adds to it a selection of accessories that includes a Knights Armament Company (KAC) Rail Interface System (RIS) railed forearm, an M68 Close Combat Optic (which is military speak for an Aimpoint Compm2 red dot optic commonly seen mounted in a Wilcox M68 30mm optic mount), a KAC 300m back-up iron sight, KAC NT4 sound suppressor, a Trijicon ACOG TA-01NSN 4x optic, an Insight Technologies AN/PEQ-2A laser designator, and an optional 9-inch-barrel M203 grenade launcher.
The SOPMOD program was developed to allow Special Operations warfighters to configure their weapons to suit their individual needs as well as particular mission requirements. The aforementioned kit has since been updated and is now known as the SOPMOD Block I kit.
As SOPMOD kits further developed over time and newer accessories were included, Block I
“how accurate you want to get is up to your budget and parts procurement skills.”
kits were updated on the fly, resulting in what some people call “Block 1.5” kits. This running update phased in Daniel Defense M4A1 RIS II and RIS II FSP, full-length railed handguards, a low-profile gas block, an Eotech 553 HWS optic, and more. A finalized SOPMOD Block II kit was eventually developed and gives users the option of using an Elcan Specterdr 1-4x Scope, AN/PEQ-15 Advanced Target Pointer Illuminator Aiming Laser (ATPIAL), and other accessories.
“the M4 became the do-all carbine of choice.”
Colt, being the original manufacturer of the M4, has an advantage over other companies that also offer M4-style rifles or upper receiver assemblies. It is said that Colt’s LE6921 Law Enforcement Carbine is as close as you can get to buying an M4 direct from the company—the major difference being that it has a semi-auto trigger group and that its barrel isn’t the exact same profile as that of the M4.
FN Herstal also offers a complete M4-style rifle under their Military Collector series. If you’re looking to build your own M4gery from the ground up, companies such as BCM and Midway USA’S AR Stoner also offer M4-style uppers at a considerable savings. Just use a forged lower of your choosing and get building. Issued M4s commonly use a full-auto bolt carrier group, standard A2 pistol grip, Milspec buffer tube extension and M4 collapsible stock. The rest is up to your interpretation.
A quick word about barrel selection: To many, M4 clones must be assembled with 14.5-inch barrels. To others, it doesn’t matter much and a 16-inch barrel will suffice. That’s a call you’ll need to make when you build your carbine. When possible, we recommend choosing a quality M4-profile barrel with a 1/7 twist that’s
It’s also good to remember that 14.5-inch length barrels like the one that comes with the LE6921 should be pinned and welded with a muzzle device that’s long enough to bring it to an overall length of at least 16 inches to be in compliance with the National Firearms Act (Nfa)—unless you plan to SBR it, that is.
We took the liberty of building several different M4 replica builds based on our research of military-issued versions. As you can see, they each differ from one another. The parts for these builds were sourced both from what is currently available at stores as well as what we found online from scouring the second-hand market.
As you may have noticed, many M4s are fitted with Kac-railed handguards. It’s worth noting that although these rails mostly look the same, there are two different versions: the RIS and the Rail Adapter System (RAS). The RIS is the older version of the two and due to how it is mounted is known to rotate ever so slightly when torqued is applied. Unlike the newer RAS, it can fit heavy profile barrels. The RAS on the other hand, also due to how it’s mounted, is much more sturdy and will not rotate. It cannot accommodate heavy barrels however. We went with the RAS versions. The equipment exchange on online forums such as Ar15.com and M4carbine.net, as well as auctions on Gunbroker.com, were great resources for us to find parts for our builds. But as with all secondary market purchases, remember that it’s a buyer beware situation. Our two cents is be careful of “too good to be true” deals.
Worth the Effort
Soon after we completed our M4gery builds, we headed to the range to have some fun with them. The process took plenty of research and parts gathering, but we feel that it was well worth the time and effort. The only problem we have now is that since completing our M4geries, the clone-building bug has really bit us hard. Lucky for us, there are plenty more variants out there… which one’s next?
M4 clones come in many different variations. The two M4 look-a-likes shown above actually use 16-inch AR Stoner barrels, which are technically incorrect since real M4s use 14.5-inch barrels.
Above: This M4 clone reflects many of the modifications implemented with SOPMOD Block I kits.
Right: A collapsible M4 stock and Matech rear flip-up back up iron sight are common to find on real M4s and their replicas.
The SOPMOD program calls this red dot the M68 Close Combat Optic. The M68 is an Aimpoint Compm2 red dot that is commonly mounted in a Wilcox M68 30mm optic mount.
An M4 profile barrel has a recessed contour that fits the mount for an M203 grenade launcher. Note the extended A2-style flash hider permanently attached to the 14.5-inch barrel to keep the gun NFA compliant.
The LMT M203 launcher seen below features a 37mm, 12-inch barrel. Authentic M203-equipped M4s commonly utilized a shorter 9-inch barrel instead.
been magnetic particle tested and chrome lined for best performance results. Mission adaptable accessories for SOPMOD kit M4s include multiple choices of optics, lights, lasers and grenade launchers. This allows clone builders a wide variety of accessories to choose from.