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Mk 12 Special Purpose Rifle
SOPMOD Special Purpose Reciever

The Mk 12 Special Purpose Rifle, used by special operations forces units of both the US Army and US Navy, is a heavily modified derivative of the familiar AR-15/M16 type. Originally intended as just a replacement upper reciever as part of the SOPMOD program, it was initially known as the Special Purpose Reciever (SPR). A decision to standardize the system as a complete weapon led to a type classification by the US Navy and the term SPR being changed to mean Special Purpose Rifle.

The Special Operations Peculiar Modification (SOPMOD) Program Management Office at Naval Surface Warfare Center, Crane Division in Crane, Indiana, provided standardized, versatile weapons accessories to meet needs across special operations forces mission scenarios. These accessories were to increase operator survivability and lethality by enhanced weapon performance, target acquisition, signature suppression, and fire control. The SOPMOD PMO provided these accessories when they were operationally suitable, affordable, sustainable, and funded.

As of 2001, the SOPMOD Block II kit was expected to feature specialized upper receivers for both long range and close quarters battle (CQB) with matching optics and noise and flash signature reduction. The long range upper was referred to as the Special Purpose Reciever (SPR), while close quarters upper was referred to as the CQB Reciever (CQBR). Development of an Enhanced Carbine, readily configurable in all 3 configurations (standard, CQB, and light sniper/automatic rifle) was proposed for the FY05 time frame.

The Special Purpose Reciever program was an outgrowth of the desire by both US Army and Navy special operations forces for a rifle with greater effective range than an M4A1 carbine, but still shorter in length than a standard issue M16A2/A4. The events of 11 September 2001 led to Emergency Combat Mission Need Statement for Special Purpose Reciever and its associated ammo. This was based on reports from SOF operators of the standard M855 being ineffective, specifically in close quarters battle situations. Experiences of the US Navy SEALs using a AR-15/M16 type carbine with a 16 inch barrel and optics, referred to as the "SEAL Recon Rifle," which had also been built by NSWC Crane, also influenced the development of the SPR component.

The first variant of the upper reciever utilized upper receivers made by either Colt or Diemaco (which was purchased in 2005 by Colt to become Colt Canada) with the integral accessory rail (referred to generally as "flat tops"). 18 inch match grade stainless steel barrels were provided by Douglas Barrels with a countor specifically for the SPR. These barrels featured the 1 in 7 inch rifling twist of the standard M16A2/A4 and M4 carbines in US military service. However, a special purpose cartridge, utilizing a 77-grain bullet was subsequently developed for specifically for the SPR, later designated as the Mk 262. An OPS Incorporated muzzle device was used, which allowed the attachment of a sound suppressor made by the same company. The handguard was a carbon fiber tube that was free floating (not attached to the barrel). These were provided by Precision Reflex Incorporated (PRI), which supplied both their original design and a second generation design for the prototypes. They also provided an early variation of their folding front sight unit, as well as a folding rear sight unit. An accessory rail, manufacturered by Atlantic Research Marketing Systems, Incorporated (ARMS), that attached to the reciever's integral accessory rail and ran the entirely length of the handguard was then attached. Various optics were used, most notably the Leupold LR M3 scope. A Versa-Pod bipod, a Chinese copy of the Parker-Hale swivel bipod, was fitted to the reciever.

Two subvariants of upper receier were subsequently developed, sometimes referred as SPR/A and SPR/B or both simply as SPR Prototype 2. The types were differentiated by the type of optic used. The SPR/A used the Leupold LR M3, while the SPR/B used the Leupold TS-30. Both replaced the PRI handguard with a variant of the Knights Armament Company (KAC) M4 Rail Accessory System (RAS), which was a component of M16A2/A4s configured as Modular Weapon Systems (MWS) in the US Army. The new version was also free floating. Along with this, the PRI sights were replaced with KAC models. The ARMS accessory rail, known as the SWAN Sleeve, was not used. Otherwise the weapons were the same. As just an upper reciever, NSWC Crane assembled the weapons using lower recievers from other weapons, mostly M16A1s and M4A1s, to retain a fully-automatic capability. Buttstock types were highly variable as a result. The lower recievers were also all modified for use with the SPR in the replacement of the standard trigger components with a KAC 2-stage match trigger system.

In 2002, the SPR element was separated from the existing SOPMOD kit, though development remained the responsibility of the SOPMOD Program. The system, to be issued as a complete weapon became known as the Special Purpose Rifle (still SPR), and was eventually designated as the Mk 12. The reconfigurable "enhanced carbine" was also split off to become first the Special Operations Forces Combat Rifle (SCR) and then the Special Operations Forces Combat Assault Rifle (SCAR).

It was unclear whether a commercial contractor assembled the weapons or whether NSWC Crane continued to assemble the weapons, but to the standard configuration. Armalite and PRI were both referenced as having potentially assembled complete weapons. The Mk 12 Mod 0 Special Purpose Rifle was of a similar configuration to the initial SPR prototype. A third generation handguard was provided by PRI for the production weapons. Complete rifles using the KAC components found on the second SPR variations were designated as Mk 12 Mod 1. Both types used the Leupold TS-30A2 scope.

There were reports that SEAL teams were apparently disappointed with the performance of the Mk 12 Special Purpose Rifle and had apparently convinced the managers at NSWC Crane continue development of the original SEAL Recon Rifle.

Also, 2 existing universal need statements were fielded by Marine Corps Combat Development Command to provide an enhanced precision firing capability at the rifle squad level. This need was met by the rifle combat optic rapidly fielded to forces in Operation Iraqi Freedom in 2003, leading the Marines to recommend the fielding of the Mk 12 Special Purpose Rifle to the Scout Sniper Platoon, where it could be used by the observers to augment the existing 8 sniper rifles with its own sub-minute of angle accuracy.

In 2004, a weapon developed by FN Herstal of Belgium was selected as the winner of the SCAR trials. The SCAR family was expected to replace the M4A1 carbine, Mk 18 Mod 0 close quarter carbine, Mk 11 sniper security rifle, Mk 12 Mod 0/1 Special Purpose Rifle, and the M14 rifle.




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