MARK 12 MOD O SPR
By Tom Beckstrand
Tactical Operator (shootingtimes.com)
Where Crane, the Creator of the MK 12, should have left well enough alone.
When the Global War on Terror (GWOT) started after 9/11, our nation’s Special Operations Forces took to the field armed with M9 pistols, M4 carbines, M24 bolt-action sniper rifles and M249 and M240 machine guns.
Some units were carrying Knight’s Armament SR-25s and Accuracy International AWM .338 Lapua Magnum sniper rifles. We had a handle on sniper rifles and machine guns, but we had one hell of an operational seam laying between our M4 carbine and the sniper rifles.
A seam occurs when there‘s a gap in one’s capabilities, a place where we lack the appropriate tools to effectively engage the enemy. The M4 works well for general running-and-gunning duties out to about 200 meters. Generally equipped with a holographic or red dot sight, the M4 is a wise choice for every man on the team.
When we stretch the distance past 200 meters, our choices (at least in the fall of 2001) quickly became limited. We could either put a scope on an M4 and hope the approximately two-MOA rack- grade accuracy was up to the task, or we could grab and/or carry an additional sniper rifle for those times when we wanted to reach out and touch someone. Neither option is a great choice.
Our nation’s Special Operations Forces quickly identified this seam in our capabilities and moved to correct the problem. The Naval Special Warfare Center, Crane Division, led the charge. Crane, with the input of our special operations soldiers, determined that an accurized 5.56mm platform was in order and that such a rifle could cover the seam in our capabilities.
THE SPR’S GREATEST STRENGTH
The greatest improvement that the SPR has over a traditional M4 is the barrel. The barrel is made by Douglas Barrels and is an 18-inch, button-rifled 1:7 twist with a rifle-length gas system. Douglas also only uses its premium barrels for the Mk 12. No barrel is ever perfectly straight, but the premium barrels on the Mk 12 are the straightest ones Douglas has and are probably much straighter than anything on a factory-produced rifle.
Douglas is well known in the custom- barrel-maker industry, and it’s rare to see a true custom barrel used on an AR- pattern rifle. This is why we’ll probably never see the Mk 12 mass-produced; the barrels are just too few in number to ever produce them in great quantity. Douglas ranks with Broughton, Pac-Nor and Shilen as the most distinguished button-rifled barrel makers in the industry. Broughton, Douglas and Shilen have all been around long enough to have multiple benchrest and F-class titles under their belts, a sure indicator of the barrel’s potential.
The Douglas barrel on the SPR also has a rifle-length gas system. The long gas system offers a couple of substantial advantages over shorter- length systems. The first and greatest advantage is that it has substantially lower port pressure than carbine- or mid-length gas systems.
As a bullet passes down the bore, the pressure behind the projectile drops because the volume the gas has to fill is increasing. The closer the gas port is to the chamber of the barrel, the higher the pressure at the port will be. Pushing the gas port of the Mk 12 all the way down to a rifle-length system means it will have the lowest pressure possible for an AR-pattern rifle.
Port pressure matters because it determines how fast the bolt and bolt carrier cycle and operate. When we first started experimenting with carbine- length systems, we found that the extractor needed some modification to handle the increased cycling speed of the carbine system as a result of its much higher port pressure. The higher pressure made the bolt carrier and bolt move faster, and that increased speed caused the extractor to fail. Hence the birth of the SOPMOD kit that puts the little rubber donut around the extractor spring to give it the additional resilience against wear.
Fast bolt issues have largely been fixed with the carbine-length gas system, and they make for supremely reliable guns. However, I still think it’s a good idea to shoot the longest gas system possible. A slow bolt is a happy bolt. It will last longer and give you fewer problems in the long run. The SPR has the longest-length gas system possible, to give the shooter the least maintenance-intensive firearm that will run for the longest amount of time.
SHOULD HAVE QUIT WHILE THEY WERE AHEAD
Crane did an excellent job with the SPR program when it created the SPR Mod 0 variant. This is the variant that we had on my first Special Forces team, and it was a popular rifle among my teammates. The Mod 0 variant I received for review features PRI’s Gen III 121/2-inch free-float fore-end.
The PRI fore-end has plenty of length for positional shooting and still leaves enough space for the addition of sling swivel mounts, lasers and night-vision equipment. The SPR fore-end also has a continuous top rail that makes it possible to mount a scope in traditional rings forward enough to give the shooter proper eye relief. Made of carbon fiber, aluminum and steel, it is an excellent combination of light weight and strength.
The round shape of the fore-end is definitely the way to go for a rifle destined for combat use. Round fore- ends tend to be much slimmer than the traditional quad rail, even before we slap rail covers all over the quad rail to keep it from biting into the support hand when using a sling or carrying the rifle for extended periods of time. The PRI fore-end has comfort, light weight and strength; it’s a winning combination for the Mod 0.
Then Crane screwed up with Mod 1. Sigh (I wish you could see me rolling my eyes as I write this). The big problem with the Mod 1 is the hand-guard. Crane went to the Knight’s Armament Rail Adaptor System (RAS) and lost the continuous top rail that came with the Mod 0 (one of its many strengths) and the slim and comfortable round fore-end. The PRI fore-end was greatly superior.
I don’t know why Crane went to the KAC fore-end, other than Crane must have some kind of special relationship with KAC. If you look at pictures of soldiers carrying the Mk 12 in combat, pay attention to how they mount their scopes on the Mod 0 versus the Mod 1. (You can find a lot of sweet action photos on mk12.net.)
Most of the scopes that soldiers mount on their rifles are in traditional scope rings because that’s what they’re issued. Scopes mounted on the Mod 0 take advantage of the continuous top rail and place the scope well forward of the seam that exists where the upper receiver and fore-end meet. The Mod 0 has a continuous top rail, so this is no problem. The continuous top rail will let a soldier do whatever he wants, optics-wise.
Now look at the pics of guys carrying the Mod 1. In those photos you’ll see the forward ring mounted all the way forward on the upper receiver and the turrets of the scope mashed all the way forward into the back of that ring. This is because the traditional quad rail will not allow the proper eye relief without a cantilevered mount. A good cantilevered mount will run about $200. That’s a lot of money to a soldier, so they make do with what they are issued and put up with the improper eye relief.
The Mk 12 Mod 0 represents the pinnacle of the SPR design as it was fielded. The great barrel, superb fore-end and continuous top rail all combine to make for an exceptionally user-friendly rifle.
The Mod 1 took a huge leap backward, but it still held on to the Douglas barrel and all of its goodness. While less than optimal, the Mod 1 is still relevant on today’s battlefield.
AN SPR WAR STORY
When I was deployed to Afghanistan, my first exposure to the SPR was my most memorable. It was an early- morning raid on a suspected Taliban hideout where we expected to find five to eight Taliban members.
Our plan required a member of the assault force, our senior weapons sergeant, to move through the target compounds with the assault element, then up onto some high ground behind the target where he could provide over- watch during the detailed search that would follow the assault. The weapons sergeant selected the SPR Mod 0 as his gun of choice.
The reason the SPR is a valuable firearm to our soldiers is that it is small and light enough to be used as a traditional carbine for house-to-house action, yet still allows the shooter to reach out to 400 to 500 meters should the need arise. Our early- morning raid was just one of many such times the SPR was called upon to perform as it was envisioned and designed.
The raid went very well. We stumbled upon many more Taliban than we initially expected (we came across between 40 and 60), but the darkness and other factors played to our advantage. Chris, the weapons sergeant, had his hands full that morning (as we all did), but at the end of the three-hour battle he was unharmed and smiling contentedly with his SPR. He engaged multiple Taliban both within and without the target structures at distances ranging from a few feet to 300 meters. That’s what the SPR was designed for, and it performed magnificently.
TIME ON THE GUN
I enjoyed the SPR Mod 0 upper that I received from PRI to review for this article; shooting the upper brought back a lot of good memories. The SPR is one of the softest-shooting ARs out there, due mostly to the excellent muzzle brake and the rifle-length gas system. The SPR makes rapidly engaging multiple targets at long distance possible, thanks in large part to the almost nonexistent recoil.
The PRI SPR I fired exhibited exceptional accuracy, and I felt like I was the limiting factor, not the rifle. The SPR’s best five-shot groups at 100 yards came from Hornady’s 55-grain A-Max, at .58 inch. Hornady 75-grain TAP came in at .7 inch, and the Black Hills 77-grain BTHP grouped at .91 inch.
I’m sure that the rifle is capable of much more—some days at the range are just better than others.
While the military occasionally makes some bone-headed decisions with its firearms, it delivered an exceptional product with the SPR, thanks in large part to the folks at PRI. If you’re looking for a premium upper capable of handling trouble from the muzzle out to whatever range you’re comfortable with, in terms of terminal ballistics, look no further than an SPR Mod 0.