How we built our own Mk12 Mod 0 SPR military rifle replica
Amovement in the firearms world that’s been rapidly gaining momentum with collectors and enthusiasts over the past few years is the replication of military spec firearms. Whether you are seeking to recreate the carbine you were issued while in the service, or want to clone the rifle of a hero, recreating a particular model or variation of a rifle or pistol to the exact specifications of a military-used weapon can be both a challenging and rewarding experience. When selecting a project to tackle, AR-15 enthusiasts in particular have many rifle variants to choose from, thanks to its use as America’s primary military-issued rifle for more than half a century. From the Vietnam-era M16A1 to today’s front-line M4A1, there are many AR-15 variants one can base a build on.
Building a Clone
“The Mk12 is a current issue M16 based rifle that is fielded by U.S. Army, Navy and Marines special operations units.”
We should mention that when we say clone, we mean to replicate, within reason, the components, attachments, accessories of a particular type of weapon used by the military at a particular point in time. How detailed it gets is up to the builder and his budget. The sky’s the limit!
We believe that some near-impossible items to procure such as receivers or accessories that are no longer made or attributes that are difficult or not possible to attain, such as select fire capability, may be replaced with alternatives. (Then again, we’re more forgiving than some of the dedicated die-hards out there.) But scoring long out of production and hard-to-find items on the secondary market is also a part of the fun of building a clone. The search goes on!
U.S. Navy Mark 12 SPR
Outfitted with an accurized barrel, using a telescopic sight and match ammunition, the Navy’s Mark 12 Special Purpose Rifle (SPR) is currently one of the most popular rifles for enthusiasts to replicate. Originally developed by United States Special Operations Command as an upper receiver kit to help supplement its carbines, the program eventually evolved into a complete weapon system. The Naval Special Warfare Center, Crane Division, helped develop the Mk12 into its final form.
Without getting deeper into its history (which can be quite convoluted and far more detailed than we have space for in this article), we’ll go over its basic specs. There are several Mk12 variants, with the Mod 0 and Mod 1 versions being the most common. The Mk12 is a current-issue M16-based rifle that is fielded by U.S. Army, Navy and Marines special operations units. You might recognize the Mk12 as the rifle used by Navy SEALS Chris Kyle and Marcus Luttrell as portrayed in the books and movies American Sniper and Lone Survivor, respectively.
At its heart, the Mk12 has an 18-inch
416R stainless steel barrel that features a rifle-length gas system. The barrel has a special “SPR” profile that allows for an OPS Inc. collar to be installed on it. An OPS Inc.
“There are several Mk12 variants, with the Mod 0 and Mod 1 versions being the most common.”
muzzle brake is also installed on the barrel so that it can fit the company’s 12th Model Suppressor. The Mk12’s barrel was designed to fire the Mk262 cartridge, which uses a match-grade 77-grain bullet.
True military Mk12s are commonly found with M16A1 or M4A1 full-auto lower receivers. Most people replicating the Mk12 choose to go with commonly found forged semi-auto AR-15 lowers instead. For those looking for an even more authentic look, Brownells, in conjunction with Nodak Spud, offers an M16a1-contoured lower receiver that they call the BRN-16A1 that closely resembles the M16A1 but with semi-auto capability.
Accessories found on Mk12s vary widely depending on the individual end user and in which time period it was used. For these reasons, Mk12 clones can differ from one another, even ones that are built to be as period-correct as possible.
Focus on Mod 0
Remember we mentioned that the history of the Mk12 can be convoluted? That’s because the rifle wasn’t developed all at one time. Using parts of used M16A1S along with other supplemented parts, the Mk12 was developed over a span of a few years. This makes tracking exactly how Mk12s were configured a bit muddled to say the least.
“Accessories found on the Mk12 vary depending on the end user and the time period in which it was used.”
Depending on which variant Mk12 you wish to build, its accessories—such as handguard, grip, trigger and even back-up iron sights— will differ. In this article, we focus our build on the Mk12 Mod 0, which is currently out of service and has been replaced by the Mod 1. There are plenty of online sources that can help you delve deeper into the exacting details of what qualifies a Mk12 as a Mk12 and the details of its different variants.
We built two Mk12 Mod 0 clones by going with two different methods and ended up with two slightly differently configured rifles.
The flat dark earth (FDE) rifle pictured here was built using a complete upper we acquired from Precision Reflex, Inc. (PRI). PRI has been supplying parts to the Mk12 program since the beginning and has staff that helped with its development.
The PRI 18-inch Mark 12 Mod 0 SPR Gen II upper comes factory-built to Mk12 specifications and includes an 18-inch, 5.56x45mm caliber Douglas 416R stainless steel barrel with a 1/7 twist rate. It comes with PRI flipup front gas block front sight and rear flip sight, rifle-length gas tube, a PRI Gas Buster charging handle with big latch, and an OPS Inc. brake and collar. The upper is completed with a PRI Gen III rifle-length carbon fiber free-float forearm that is Cerakoted in FDE finish. It is topped with a PRI full-length top rail with PEQII removable rail section.
Typical of building a clone of a rifle that has since been out of use, we had to use a newer model of an item that has gone out of production. Sitting atop the upper is a Leupold Mark 4 2.5-8x36 MR/T M2 (112633) scope, which according to our research is the closest current production optic to the original Leupold TS-30 or TS-30 A2 scopes that were originally used on the Mod 0. The scope sits in A.R.M.S. #22 Medium rings that are equipped with a #22 Tactical Ring Cap and a #22 Tactical Ring Rail. It also sports a Harris HBRMS Bipod in A.R.M.S. #32 throw lever bipod adapter.
Completing our FDE clone is the aforementioned custom Cerakoted Brownells BRN-16A1 lower that closely resembles an M16A1 lower’s contours. We finished it off with a Brownells AR-15 lower parts kit, an Ergo Surgrip, PRI A2 stock assembly and Geissele SSA-E two-stage trigger.
For the black-colored clone, we took a different build approach. We decided to assemble the Mk12 Mod 0 upper from the ground up, sourcing what parts we could from what is currently in production. Again, we looked toward PRI for some of the major parts including the 18-inch Douglas 416R stainless barrel in a black finish. We also got other PRI Mk12 Mod 0 staples such as their Gen II Retro Carbon Fiber rifle-length forearm, G2 flip-up front gas block front sight and M84 Gas Buster big latch charging handle.
Completing the upper receiver assembly is a BCM M4 upper receiver, Allen Engineering AEMB brake and SPR collar (word on the street is that Allen makes them for OPS Inc.), Strike Industries rifle-length gas tube
“We decided to assemble the Mk12 Mod 0 upper from ground up, sourcing what parts we could from what is currently in production.”
and Brownells M16 nitride-coated bolt carrier group.
Accessorizing the upper, we opted for an A.R.M.S. #38 S-EX Swan Sleeve and #40L low-profile rear sight, which are what many original Mod 0 rifles were outfitted with. Again, instead of scouring the secondary market for an original scope, we opted for a current day contemporary. The Leupold Mark 4 LR/T 3.5-10x40mm (67945) has an illuminated Mil Dot reticle and is outfitted with their M3 turrets. It sits in the same A.R.M.S. ring setup as our FDE Mk12. A Harris Bipod with A.R.M.S. #32 bipod adapter rounds out the upper assembly.
For the lower half, we went with an Andersen Machine forged lower receiver complete with Brownells lower parts kit. To stay true to the Mod 0 build theme, we installed a Knights Armament 4.5-pound 2-stage match trigger, the same trigger that many original Mod 0 rifles used. We also sourced an Ergo grip and an A2 stock assembly by UTG to complete the build.
Difference in the Details
Minus the color, at a glance the two Mk12 Mod 0 clones look just about identical. But
to the discerning eye, you’ll notice some visual cues that set the two apart. The main difference becomes obvious when you study the top rails and rear sights on the upper receivers. The FDE rifle features a PRI top rail and rear sight while the black rifle uses ones by A.R.M.S. For those keeping score, the A.R.M.S. version is more correct for a Mod 0 clone according to our research.
You’ll also notice that the collar on the FDE rifle is a bit shorter than the black version and that its setscrew faces 12 o’clock while the black one has its setscrew facing 6 o’clock. Which one is correct? Perhaps both. More research will be required. As you can see, building a clone requires plenty of research and dedication if you want to get every detail right.
“With our clones complete, we admired their beauty and promptly headed off to the range to really enjoy them.”
There are many AR-15 variants one can choose to clone. The Mk12 Mod 0 is a popular choice.
The Mk12 Mod 0 utilizes an 18-inch, 5.56 caliber Douglas 416R stainless steel barrel and a PRI Gen II Retro Carbon Fiber rifle-length forearm.
Right: Allen Engineering’s AEM5 silencer is a popular equivalent used on many clones.
Far Right: A proper Mk12 clone uses A.R.M.S. #22 scope rings, ring cap and ring rail for its scope mount.
Far Right: Pri’s M84 Gas Buster charging handle is correct for Mk12 builds.
Right: Mk12s were originally issued with OPS Inc. 12th Model Suppressors.
Right: Our clones use different top rail sleeves. The FDE uses a PRI full-length top rail while the black one uses the A.R.M.S. #38 S-EX.
Sourcing all the parts to assemble the Mk12 Mod 0 upper from the ground up can be a challenge, but is definitely worth the effort.
Although both of our Mk12 Mod 0 clones look similar, to the discerning eye, you’ll notice some visual cues that set the two apart.
Original Mk12’s use Colt M16 A1 select-fire lower receivers similar to this Colt M16 A2. Note the full-auto fire trigger group.