THE MK12 (SPR) RIFLE
SYSTEM
Top to Bottom: USMC SAM-R, MK12 MOD1 and MK12MOD0
The MK12 rifle system was originally conceived by Mark Westrom of Armalite and developed by the Crane Naval Surface Warfare Center in Crane, Indiana. SOCOM wanted a drop-in upper receiver to fit standard M16 lowers that would fill the role of a light sniper rifle for use by Special Operations teams deployed far from the support of conventional forces. At that time (late 1990s) there was nothing commercially available that would meet their specifications. As prototypes were tested the MK12 or SPR as it is commonly known evolved as a scoped rifle with an 18. free-floated barrel designed for Black Hills 77 grain match ammunition designated MK262. The best description of MK12 development I am aware of can be found in Christopher Bartocci.s book BLACK RIFLE II published by Collector Grade Publications. Very little information is available in the public domain about the MK12 rifle system although some MK12 MOD1 rifles are currently being deployed with USMC units in Afghanistan so hopefully we will learn more in the near future.
I was told by CWO John Miller, one of the original assemblers of these rifles, that they were responsible for a significant number of enemy kills in the sand box and SOCOM was somewhat secretive about the weapon. To this day I have never been able to get my hands on a copy of an original manual.
MK12, MOD0
The original SPR adopted for military use was designated MK12 MOD0. This early rifle utilized readily available M16A1 lower receivers fitted with a Knight.s Armament match grade trigger which retained the select fire capability of earlier M16 series weapons. The upper receiver was a standard Colt M4 part cut for extended feed ramps. An 18. Douglas medium weight stainless steel 1/7 twist match grade barrel with M4 barrel extension was selected for use on production rifles. This barrel utilized a standard length (rifle) gas tube. The original barrels were supplied by Gene Barnett. Gene was a NCO assigned to the National Guard Marksmanship Training Unit who spent many years producing M14 match barrels for military rifle teams when NGMTU was located near Nashville, TN. Knowledgeable people have stated that Gene knows more about M14 and M1 barrels than anyone else currently alive. He is now retired.
The barrel was free-floated with a carbon fiber tube produced by Precision Reflex of New Bremen, Ohio. There were problems with these early production PRI forends. The threaded section at the rear of the tube which attached to the barrel nut was not always epoxied in place parallel to the forend itself and there were an unacceptably high number of rejects. I do not believe these original Gen. II tubes are still commercially available. Sections of 1913 rail are attached to the forward end of the tube with screws and retaining plates. A special top rail was produced by Atlantic Research Marketing Systems (A.R.M.S., Inc.) designated the #38 Swan Sleeve which clamped to the upper receiver and attached to the PRI tube with screws. This sleeve provided an uninterrupted mounting surface for optics and accessories which extended from the rear sight to the front sight. One has to keep in mind that there was not a plethora of railed forends for M16s on the market in 1999 like there is today and 1913 rails on free-floating M16 forends was a pretty advanced concept at that time. An ARMS #40 rear sight was integrated into a radius cut at the rear of the rail as a backup iron sight.
The unique front sight/gas block assembly was also produced by PRI. The folding front sight incorporated an elevation wheel. These assemblies were never offered to the public. Original gas blocks were designed to be attached with screws although I believe Crane later pinned them.
The MK12 was designed to be used in conjunction with a sound suppressor. A tapered sleeve is installed on the barrel prior to fitting the muzzle brake. This sleeve centers the rear of the OPS, Inc. 12th model suppressor. The muzzle brake, also produced by OPS, Inc., is externally threaded to accept the can. I have found the brake to be quite effective and point of impact shift when attaching the can is negligible. These 12th model cans are available on a limited basis from OPS, Inc. and some distributors of their products. The suppressor is supplied with the muzzle device.
MK12, MOD1
The MOD1 version of the SPR differs from the MOD0 only in the forend. MOD0s are supplied with a conventional aluminum free-floating RAS (Rail Adapter System) part number 99167. The full length ARMS #38 top rail is not installed on this model. Iron sights consist of a Knight.s rail mounted folding front sight and 600M folding rear sight. A conventional gas block is used on this model.
Optics for both models of the SPR were supplied by Leupold. The commercial versions of these scopes were marketed as the Mark 4 3-9x36mm MR/T with M3 knobs.
The scopes were mounted in ARMS #22 high throw-lever rings.
Further reading:
BLACK RIFLE II by Christopher Bartocci published by Collector Grade Publications
SHOTGUN NEWS February 10th 2005 edition. Article by David Fortier titled .Precision Rifle and Light Support Weapon: The Special Forces Deadly MK12 MOD0.
