The AR-10 is nothing new. It is where the AR-15 and the whole American-made black rifle market began. The AR-10, chambered in .308, is a clear descendent of the heavy battle rifles that dominated early 20th century wars. The prevailing wisdom decided that soldiers needed heavy rounds that offered reliable stopping power at long ranges. These were considered opinions that wanted a rifle platformed that mirrored the abilities of the Garand and M-14. Yet they also knew that speed and capacity and modularity were important.
At the other end of the table were those who wanted smaller, faster rounds, and more of them. These dudes eventually won the debate. But the AR-10 platform didn’t go away. The draw of the .308 is still strong, and the desire for the perfect delivery system has driven companies like CMMG to continue to develop the basic AR-10 premise. Their Mk3 is a big-ass .308 that delivers on the promise of the AR-10: the stopping power of a heavy round, the fighting versatility of a lighter, faster rifle.
Those descriptions are relative. Most .308 bullets weigh three times what a .223 bullet weighs–sometimes more. From some bolt guns, the .308 is capable of reliable 1,000 yard accuracy–sometimes more. Yet that’s not the task of the Mk3. This is a battle rifle, not a sniper rifle. It is meant for engagements in that point-blank to 300 yard range, with the certain understanding that it could be called on for longer shots if needed. It is light enough to actually carry. Its capacity is limited only by the capacity of its magazine, which is easy to change. While it is more suited to a shooter with a robust frame, there is a place for the Mk3 along side an AR-15 and a bolt action with incredible range.
- Caliber: 308 WIN
- Barrel: 16.1” 1:10 twist, medium tapered, 416SS, SBN
- Muzzle: CMMG SV brake, threaded 5/8-24
- Hand Guard: CMMG RKM15
- Furniture: Magpul MOE pistol grip, ACS-L butt stock
- Receivers: Billet 6061-T6 AL LR308 type
- Trigger: Geissele Automatics SSA
- Weight: 8.7 lbs (unloaded)
- Length: 36” (stock collapsed)
- Gas Port Location: Rifle
- MSRP $1,999.95
Fit and Finish
The build on the CMMG is predictably good. These are solid guns, made well. This is the second CMMG I’ve reviewed, and I’ve seen numerous other examples. All seem to have the build quality that’s commensurate with what one would expect from a modular rifle in this price range. There are tool marks. Look at the photos above, you can see what I’m talking about. But all of the pieces fit and function well.
They have to. When companies build guns from component parts, like Magpul’s furniture, everything has to fit. And there’s no reason why there should be a higher level of finish detail. The stamps are clear, the edges of the upper and lower fit flush, there’s no creep in the Geissele trigger…. In short, everything that you expect to work does, reliably. It isn’t the most highly polished build you will see, but it is miles away from the worst build you can find out there.
How does it shoot?
I can clearly remember the first time I shot an AR-15. Hell, I remember the first time I held an AR. It was a formative experience. I blew through hundreds of rounds of .223, marveling at the responsiveness of the gun and the speed at which I could empty the magazines. Nothing after has come as close to that moment.
Taking it to the next level, ballistics wise (as the Mk3 clearly does), is also a heady experience. And it is tiring. The speed is clearly there. Yet the recoil is more intense. The gun is heavier. Rapid fire knocks you off balance a bit faster. At the end of a range day with the Mk 3, I haven’t shot as many rounds, but I feel like I’ve shot hundreds more than I have.
At short distances this gun would be devastating. With the 16 inch barrel, the Mk3 remains maneuverable. The collapsible stock allows the Mk3 to be even more compact. It clearly isn’t as small as a similarly sized AR-15, but it is comparable, and that’s what’s important. Run head to head, the AR-15 would be only slightly more maneuverable, and slightly faster. But the .308 is going to hit a lot harder. If you were attempting to disable a vehicle, this would be your logical choice. If you were shooting through cover, this would be more effective. If you wanted a rifle that would hit hard at 25 yards, and then hit hard at 300 yards–the Mk3 is a great choice.
And that’s how I’ve been thinking about the Mk3. I’m not manning a checkpoint. But I do hunt. The Mk3 would be a solid hunting gun for where I live (where most practical ranges extend to 200 yards at most). The Mk3 would also be good for some elk, moose, or bear hunts. The speed and higher capacity of the Mk3 would make it very effective as a brush gun. I guided up in the Boundary Waters Canoe Area for a while, and flushed moose more than once ( and some at terrifyingly close distances). The Mk3 would have been ideal for some of those situations.
And if there was ever some sort of end-of-the-world sort of kerfuffle, I’d want something like this in my available arsenal.
And close range accuracy is spot on. We zeroed the Mk3 at 50 yards, then stretched it out to 100, 200, and 300. Predictably, the farther out we got, the less likely we were to score exacting hits. But look at what the gun is capable of up close.
The heavier rounds were tripping the chronograph around 2,400 FPS, give or take. Lighter 150 grain rounds were approaching 2,600. These are respectable speeds for heavy rounds that carry a lot of speed, even at long distances.
Some of the variation we saw came from grain weights. I’ve shot lots of .308s, and some of them will eat just about anything you feed them. The Mk 3 has a distinct preference for heavier rounds. And it doesn’t like the soft tipped bullets at all. As the bolt rockets back into position, it breaks the soft tips of the Nosler pictured below clean off (which doesn’t improve accuracy, at all). I stone cold wasted a box of Nosler before I figured this out. “What are all of these whit things?”
What kind of accuracy can you expect?
I’d say the Mk3 is capable of 1 MOA–to a point. We got 1 MOA at 100 yards, and at 50 yards–though that accuracy didn’t hold at longer distances. We’ve had this gun in for review now for several months, and have worked it out slowly, and here’s what we’ve found.
First, it gets hot quickly. That heat translates into wider spreads. In order to achieve anything close to MOA accuracy, we had to let the gun cool down between shots. This made the review process take a bit longer, but we eventually worked out a schedule that allowed us to shoot a round out of the Mk 3, then move to other guns–only returning after the gun had cooled.
The heat is one issue, but the basic design is another. Loading may be rough on rounds–we covered that. Any deformation in bullet shape is going to result in erratic flight. But there’s more. The placement of the gas block on the rail has long been a problem that plagues the AR platforms, both AR-15s and AR-10s. This system isn’t as inherently accurate as free-floated bolt guns in similar calibers. It can be, but it usually isn’t.
And when you look at the way the Mk3 stabilizes rounds, you’ll begin to see a pattern. Or I did. The heavier rounds held course and were much more likely to hit where you want. The same 155 grain bullets that shot close to 1 MOA at 100, were all over the target at 300.
I happened to have a really wide variety of .308 during the various shoots with the Mk3. I had 10 different varieties of Hornady, alone. While some of the light recoil rounds at the lower end of the grain weight spectrum worked fine, they were useless at any real distance. Moving up, though, from 125 to 150, to 155, to 165, 168, and finally 178, we saw better groups. But even using the word “group” is generous for our 300 yard attempts. We got hits that would have been effective kill shots from that distance, but not groups.
A 1 MOA group, at 300 yards, measures just over 3 inches. Despite all of our efforts at control, we couldn’t make that happen. I’ve read up on Mk3 accuracy. The forums all have dedicated CMMG conversations. Some folks are reporting less accuracy at even closer ranges, but they are almost all relying on light ammo. Others seem to be getting marginally better accuracy after pairing specific ammo brands and grain weights. There’s a growing group that sees the CMMG Mk3 as a great platform on which to build a super accurate rifle. They’re replacing the gas blocks and fine tuning the guns and getting stellar results.
If this were my gun, and not one I had to return, I’d put on an adjustable gas system that would allow me to run wide open or suppressed. The Mk3 with some night vision would make a vicious hog hunting gun.
I’m a fan of this gun, as is. Other than a couple of Nosler rounds with broken tips getting jammed up while feeding, we had no reliability problems. We’ve put several hundred rounds through this–every flavor of .308 we could literally get our hands on–and more than one can of steel-cased Tula (because we do so like the super-hero like thrill that comes from banging steel with lead, and the throbbing shoulder pain that comes from such run-and-gun fun). No failures to eject. No light primer strikes. Ejection was consistent and reliable. Brass wasn’t mangled.
If anything, I’d say this is a gun that is ideal for someone my size. Once you take advantage of all of the key-mod space on the rail, you will end up with a heavier rifle. This gun starts at 8.5 pounds. After a forward hand stop, a light, a scope, a full magazine, a strap-this is going to get heavier. But it is a heavier rifle. It is meant to bridge a gap that exists between the featherweight carbines and the slow precision of the sniper. It is a designated marksman’s rifle. And it would put meat on the table. It may be heavy, but it is one hell of a versatile gun.