• Manufacturer: Naval Surface Warfare Center - Crane Division
  • Model: Mk12 Mod 0/1 SPR
  • Caliber: 223 rem / 5.56x45mm NATO
  • Barrel: Douglas Premium Air Gauged - SPR Profile
  • Barrel Length: 18" (457mm)
  • Twist: 1:7"
  • Magazine: 20 or 30 Round Detachable Box (M16)
  • Trigger: Knight Armament Corp. Selective Fire Trigger Group (Early), Geissele SSA-E (Late)
  • Stock: M16A1, A2 Fixed, M4 Collapsible, or Crane Enhanced telescoping
  • Weight: About 10lbs with optics and fully loaded magazine

When the USA entered the global war on terror in 2001, the various special operations branches of the US military soon discovered that they needed a weapon that would slot between the M4 and the M24 Sniper rifles in order to give the groups a bit more reach without having to resort to the heavier and slower bolt action sniper rifles. The decommissioning of the M21 and failure to adopt the XM25 on a wide scale basis plus their larger size, partially lead to the gap in capability with the available weapons systems at the time. The M24 was great for delivering long range precision fire, but the special operations teams needed to be able to deliver a lot of precision fire at ranges beyond the capabilities of the M4 and M16 rifles, and at a much faster rate than the M24 could deliver. The size and weight were also a factor as the rifles needed to be more portable for use in the dynamic war zone the teams found themselves in.

The envisioned role for this rifle would be something similar to a Designated Marksman, but tailored for special operations. The SEAL teams were the ones that were the most proactive in moving this initiative forward. The SEAL team armorers started coming up with their own accurized M4s that fit their needs. The teams were calling these the SEAL Recon or Recce Rifles. Each armorer had their own little tweaks and mods that they preferred so the Recce Rifle was a bit different between each of the teams. The basic concept was an M4 with optics and some parts to improve accuracy to allow more precise shot placement at longer ranges than their M4s were capable of. As the concept gained acceptance, the Naval Surface Warfare Center used their Crane Division to begin working on a formalized version of the Recce Rifle. The resulting concept that they came up with was what they called the Special Purpose Rifle, or SPR.

Initially the SPR was to be a Special Purpose Receiver that would replace the upper receiver on a standard M-16 rifle. As Crane continued with the development, the “receiver” concept was eventually discarded and a complete rifle was developed specifically for U.S. Special Operation Command (SOCOM). The SPR went through several developmental iterations before the specifics were settled on and the initial batch of Mk 12 Mod 0 rifles were fielded in 2002. (Pronounced ‘Mark Twelve’). The SEAL Recon Rifle, and subsequently the SPR, was always intended to be used with the new enhanced and longer range M262 77gr 5.56x45mm NATO ammo that was being loaded by Blackhills for the special operations branches.

Sniper Central Ballistic Cards

The Mk262 ammunition was developed to enhance both the lethality of the 5.56 NATO round as well as its effective range. The 77gr OTM (Open Tipped Match) bullet does much better at longer ranges than the standard 62gr M855 ammo, but it also requires a fast 1:7″ twist barrel and the barrel is where Crane started with the SPR rifle. The barrel is a Douglas Premium Air Gauged match barrel with a twist of 1:7″ and 18″ long. Different barrel lengths were tested and finally it was settled on 18″ to provide a good compromise between portability and performance. The barrel also uses the longer rifle length gas system that reduces gas pressures and slows down the bolt cycle for longer life and improved reliability. The length of the barrel is somewhat lengthened by the addition of the Ops Inc. muzzlebrake and collar for use with the Ops Inc. suppressor. The contour of the barrel is unique and is designed to reduce weight while maintaining rigidity for accuracy and is now known as an ‘SPR contour’.

Upper receivers were all flattop M4 uppers made by Colt with some others used from Diemaco and Armalite. They used standard M-16 bolt carrier groups and a rifle length Precision Reflex (PRI) Gen I carbon fiber handguard. The lower receivers were also Colt made with some others labeled GM Hydramatic. One of the interesting things about the lower receiver is that they used old M-16A1 lowers on all of the SPR rifles so the original rifles had the M-16A1 or A2 fixed buttstocks and standard A1 or A2 grips. Over time as the different versions of the SPR rifles were introduced, the buttstocks and grips changed a bit, but the receivers were all still M-16A1 receivers. The trigger group was changed out to a Knights Armament 2-Stage full auto match trigger to improve accuracy. This too was changed out in later versions to the Geissele SSF trigger which proved more reliable.

Accuracy with the Mk262Mod1 ammo was very good with accuracy well under MOA. The heavier 77gr bullet allowed for the rifles to maintain that accuracy to ranges reaching beyond 600 yards. The combination of rifle, suppressor, ammo, and skilled operator made for a lethal package for many engagement scenarios.

Because these rifles were developed for, and extensively used by the Special Operations units, these units freely made their own changes and requested their own specific optics and other parts be used on their rifles. Typical scopes found on the SPR included Leupold Mk4 10x40mm, Leupold 3.5-10x40mm (illum), Leupold 3-9x36mm (illum), Nightforce 2.5-10x24mm, and some others. Once in the rifles were in the field, many other scopes were also used including Red Dots, Premier Reticle scopes, Schmidt & Bender ShortDots, etc. The field modifications were not limited to just the optics either.

From Crane, the rifles came in a Pelican 1700 hard rifle case with cutouts for all of the accessories including the rifle, optics, suppressor, magazines, cleaning kits and other odds and ends.

The official SPR versions changed over the next decade with the biggest change happening from the Mod 0 to Mod 1 versions which included a change from the PRI handguard to a Knights Armament Match FF RAS setup which removed the monolithic rail all the way across the top. This change was one which many operators complained about. There were several other changes included in the Mod 1 as well. A Mod H , or Holland, version was also rolled out for one specific SF team and it included a 16″ barrel and went back to a PRI handguard.

The SPR, especially the Mod 0, was loved by the operators from all branches of Special Operations, especially when it was compared with the M110SASS rifles. The SPR was reported to have been made to very high tolerances and was much more reliable than the more mass produced M110 rifles. The SPR was often times preferred over the SASS even when considering the smaller and less capable 5.56 cartridge versus the 7.62 used in the M110SASS. The Mk12 SPR has since been replaced by the Mk16, Mk17 and M110 rifles, but the SPR is still used by a few of the SEAL teams and it still maintains almost a cult like following among the special operations groups. It had even gotten to the point where the teams horded them like gold for as along as possible.

The SPR even found use among the USMC with it being utilized as a Designated Marksman rifle among normal line units.

The history of the SPR is fascinating and they were used extensively in combat so they come with a proven combat record as well. Some people may even go so far as to say the SPR was the pinnacle of the Ar15 development over the last 50 years. What ever your personal feelings are about the SPR, they were a very effective DM style rifle with confirmed kills out to and beyond 800 yards. All from a light and compact M16 based rifle. That rates as pretty high in our book.

Note: If you are interested in owning one of these for yourself, check out the Sniper Central Heritage Mk12 SPR.

Sniper Central



An 18-inch (457 mm) threaded-muzzle match-grade free floating stainless steel heavy barrel with a 1:7 (178 mm) rifling twist ratio is standard for the SPR. The barrels are manufactured by Douglas Barrels with a unique contour that reduced weight but maintained rigidity for accuracy.


In 2014, Ops, Inc stopped manufacturing this model of suppressors. The equivalent product is currently manufactured by Allen Engineering Co. as the AEM5. It is substantially the same suppressor design and actually built by the same individual, Ron Allen, who previously fabricated the h model suppressor for Ops, Inc. Due to the limits in terminal performance and relatively poor accuracy of the 62-grain (4 g) M855 ball, the Mk 262 Open Tip Match (OTM) round was developed as a more accurate round for the SPR, and manufactured by Black Hills Ammunition. The first production batches were designated Mk 262 Mod 0 and used a Sierra Bullets MatchKing 77-grain (5 g) Hollow Point Boat Tail bullet without a cannelure (crimping groove).


Sorry if I’m resurrecting a zombie thread, but the Ops/Allen can is now being made by Otter Creek. The king is dead, long live the king!


Very good history on the Mk12 that I followed closely but had long forgotten about until recently! The reason I started back into the info on this is MSGT Steve Holland of 5th Group (Apologies Steve if I’m off on your rank) – Steve worked not just on the
“mod Holland” version but also the original Mod 0 for US Army Special Forces. He was in it from the beggining, whether at the same time as Navy was OK, but I trust what he as said in his word of mouth talking about the Mk12 developement that he was a part of the project and lead in many respects, including the work on the SPC line that was finalized as 6.8 mm projectile, even if never adopted the effect on shaking up the system to look at something intermediate between 7.62nato and 556 was very important.


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