July 16, 2015
By David Fortier
The 7.62x39 is not just a cartridge. It is one of the most significant military rounds of the 20th century. Mated to the RPD, SKS-45 and AK-47, it redrew boundaries around the globe, toppling old empires and creating new ones. However, as important as it has been to combatants from the days when the United States fought in the jungles of Vietnam to today's battles in the Middle East and elsewhere, the 7.62x39 excels at nothing in particular. It was specifically designed as a compromise, and no one has ever raved about its sterling accuracy or long-range capabilities.
So I felt a bit silly trying to judge the wind with a round of 7.62x39 full metal jacket sitting in the chamber. But the planets had aligned, and on this February day in Kansas, I had nearly perfect conditions. It was a sunny 50 degrees with almost no wind, and 730 yards away stood a single Action Target silhouette. Resting on the railing of my shooting tower was CMMG's new Mk47 Mutant in 7.62x39. I was getting ready to call it a day when I decided to give this distant steel plate a go. Sheer folly, right?
The rifle in question is a new design from CMMG that blends East and West. In simplest terms, it is an AR-pattern rifle in 7.62x39 that feeds from standard Kalashnikov AK-47/AK-M magazines. It's not built on a straight-up AR-15 platform but rather one larger than an AR-15 but smaller than an AR-10. Hence the "Mutant" moniker; it is in between the two traditional AR sizes.
Why would anyone want to do this? Why not stick with, say, a standard AR-15 in .300 BLK? Good question. One reason would be economy. Imported steel-case 7.62x39 ammunition is both plentiful and reasonably priced. It is dirt cheap compared to brass-case .300 BLK or 6.8mm SPC. There are certain things the Russians do well, and one of them is churning out economical ammunition by the shipping container.
Performance-wise the 7.62x39 has a slight advantage over the .300 BLK when it comes to case capacity and velocity. When loaded with modern expanding bullets, the terminal ballistics of the 7.62x39 is vastly improved over the old M43 steel-core ball load American troops encountered in Vietnam. Modern bullets really wake up this cartridge, and it works well on deer and hogs inside 200 yards. It also penetrates intermediate barriers well. Today there are a number of excellent loads available for this old Soviet cartridge. Plus, like the Blackout, it even works well when loaded to subsonic levels for suppressor use.
However, when it comes to AR-pattern rifles, the 7.62x39 has a problem. It has a pronounced case taper, which aids extraction but also dictates an equally pronounced curve in the magazine. This was not an issue for the AK-47, where the magazine well, bolt and magazine were all designed to work together. But if you try to drop the 7.62x39 into an AR-15, you run into problems with the standard AR-15 magazine well. The 7.62x39 cartridge stack wants to curve before the straight AR-15 magazine well will allow it. Yes, 7.62x39 magazines are available to fit standard AR-15 lower receivers, but this solution is hardly ideal. Reliability is always suspect. Some guns run them all the time, some most of the time and others are problem children. Plus, the quality of these magazines often leaves a bit to be desired, especially when it comes to durability.
The obvious solution, then, is to simply use AK-pattern magazines in your AR-15, right? This is not a new concept. Even the U.S. military took a great interest in the possibilities. While it has been done — I own an MGI Hydra that ticks along nicely — all is not roses. While AR-15 magazines are thin, light and made to be disposable, AK magazines are thick, durable and capable of being used as an improvised impact weapon. So their sheer size, namely width, pre-sents a problem for both the AR lower and upper receiver. Plus, the AR-15 bolt was not designed to strip rounds from such a beefy magazine. The bolt has to be able to reach far enough down inside the magazine to reliably strip a cartridge from the feed lips and chamber it. The AR-15 bolt's design is not optimum for this.
Then there is the issue of the bolt itself. An AR-15 bolt needs to be opened up to accommodate the larger diameter case head. This in turn weakens it, and it is not unheard of for bargain-basement 7.62x39 AR-15s to break bolts.
CMMG looked at the different issues various manufacturers had encountered with building a 7.62x39 AR-15 and decided to do something different. Rather than trying to cram an AK-47/AK-M magazine into an AR-15-size upper and lower, the company decided to give itself some room. At first glance it appears engineers simply built the Mk47 Mutant on an AR-10-size platform, but they did not. The Mk47 is noticeably larger than an AR-15 but quite a bit smaller than an AR-10. The size relationship became clear to me when I laid out a stripped Mk47 next to a 7.62x39 MGI Hydra AR-15 and a Les Baer .308.
The rifle's heavy-walled upper receiver is machined from 7075 T-6 and is based on CMMG's own .308 Win. MK3 series. This flattop design features a dust cover and brass deflector but no forward assist. Inside of this rides an AR-10-type bolt designed for this application. It dwarfs a standard AR-15 bolt when placed alongside. As such, it is overbuilt with strength to spare.
The machined bolt carrier is noticeably bigger and heavier than an AR-15's but smaller and lighter than a standard AR-10 carrier. The CMMG Mk47's bolt carrier weighs 17.2 ounces, compared to carriers from the aforementioned MGI and Les Baer rifles, which weigh 11.2 and 18.75 ounces respectively. The Mk47's heavy bolt carrier assembly works in conjunction with a specially marked buffer that weighs 3.9 ounces, about the same as an AR-15 H1 buffer.
Mated to the front of the upper receiver is a fairly light 16.1-inch barrel with a 1:10 twist. This is free-floated to enhance accuracy and features a traditional AR carbine-length gas system with a low-profile gas block. Surrounding the barrel and Stoner gas tube is a CMMG RKM15 Key Mod handguard system. This extends almost to the muzzle and features a 1913 rail at 12 o'clock and Key Mod slots at three, six and nine o'clock for easy mounting of accessories. An SV muzzle brake is fitted to reduce recoil and muzzle movement.
The lower receiver is where things really get interesting. Gone is the conventional AR-15 magazine well and in its place is a piece redesigned to accept AK-47/AK-M magazines. This features a replaceable steel front engagement point and an oversize paddle release. The release has been designed to allow manipulation conventionally or using your trigger finger. There is no bolt catch, and the bolt does not lock back on the last shot. The rifle sports standard AR-15 firing components and an AR-15 carbine receiver extension. A Magpul CTR stock and MOE pistol grip came on my review rifle.
One of the downsides to my 7.62x39 MGI is it is picky when it comes to magazines. Only steel AK-47/AK-M magazines work, and not all of them. The magazine well is too tight for polymer and Bakelite magazines. So I was interested to see if the Mk47 would accept a variety of military and commercial magazines, as these vary in dimension.
Sifting through what I had kicking around the shop, I found the Mk47 easily accepted European- and Chinese-pattern steel AK-47/AK-M magazines and Soviet Bakelite magazines, along with a 75-round Chinese-pattern drum. Soviet, Polish and Bulgarian pattern polymer mil-spec magazines were tighter but locked into place with some effort — as did commercial I.O. Inc. polymer magazines. The only magazine that would not fit was a European-pattern 75-round drum.
The Mk47 ships with Magpul magazines, and these worked fine. I did most of my bench testing using Hungarian 20-round steel magazines.
Next, I assembled six different 7.62x39 loads to see just how well CMMG's Mk47 Mutant performed. Included were both economical imported steel case and high-end domestic loads. For accuracy testing from the bench, I mounted a Hi-Lux 4-20x50mm PentaLux tactical scope I had in for a different project. I figured the higher magnification would be an aid.
Using Hungarian 20-round steel magazines, I proceeded to fire four five-shot groups with each load from a rest at 100 yards. While rounds fed smoothly and chambered without issue, I immediately noticed an oversized charging handle would be an asset on this piece. My review gun had a standard AR-15 trigger group, and it was heavy but usable. Ejection was to three o'clock, and recoil was mild. All in all, it was a pleasant rifle to shoot from the bench.
Accuracy was quite acceptable. Results are shown in the accompanying table. Best individual groups went to Wolf and Winchester Hog ammo at 1.7 inches, and the Mk47 Mutant shot respectably well across the board.
The bad news is functioning was not 100 percent with two loads. The Hornady 123-grain SST load posted an average velocity of just 2,262 fps, which is about 70 fps slower than I'd expect and which led to occasional short-
stroking. The Magsafe load's pressure curve was all wrong for the Mk47 and would not cycle. The rest of the loads ran flawlessly, and there were no magazine problems of any kind.
Moving from the bench, I shot all six loads from various field positions on steel plates at 100 yards. Running drills here showed the Mk47 to handle well, but reloads are slower than a standard AR. The magazine release works well enough, and its length provides plenty of leverage, but the lack of a bolt hold-open is a bit of a hindrance. Next I tried my hand at hitting 11x20-inch LaRues placed from 200 out to 330 yards. Here the CMMG Mk47/Hi-Lux combo performed well. The rifle was comfortable to shoot, and no issues were encountered. Practical accuracy shooting from the prone position was quite acceptable at the distances where one would use this cartridge. In my opinion, the 7.62x39 is at its best inside 300 yards.
As I wrote at the outset, I also shot the rifle at a full-size silhouette at 730 yards. This is well beyond the distance one would normally use a 7.62x39, but I was having fun and had some ammunition left. I had no spotter, but the dirt was dry enough to spot hits. It took me five rounds to figure out elevation and windage, and then I fired another 15 rounds at a leisurely pace. I was surprised by the amount of paint I could see being removed from the target, and when I drove down to the target I found 11 fresh impacts. It's certainly no match gun, but you can do quite a bit with an honest two-minute rifle.
CMMG's Mk47 Mutant is an interesting solution to an old problem. Kalashnikov magazines actually fit, and the bolt is overbuilt for the application and should live to a ripe old age. Practical accuracy proved acceptable and consistent. I'd prefer a slightly shorter handguard, a better trigger (which is available as an option) and an extended charging handle. All in all, though, the Mk47 Mutant would make a great plinker and short-range deer or hog gun. Currently, CMMG offers three models with retail prices starting at $1,500. The Mk47 Mutant AKM seen here is the middle model, which retails for $1,650.