The 7.62x39mm PWS Diablo upper receiver worked well with the author’s registered SBR lower, providing compact yet capable firepower. Note the small size of the SBR with its short 7” barrel and collapsed stock.

I am always on the lookout for weapons chambered in the 7.62x39mm round. As much as the ergonomics of the AR-15 suit me, the 5.56mm cartridge has never been a preference, but getting AR platform rifles to work well has been a bit problematic. Given a military application the preference would be the 7.62x51mm, but in the law enforcement world, especially for entry, it has not caught on because of liabilities and perception issues. Any weapon a police officer uses will be scrutinized heavily and changes have to be made carefully. Quite often it is less about the weapon or the cartridge, but how it looks. It is one of the reasons the AK47, especially in its standard form, has not been widely adopted. Fortunately that is changing to a degree, mostly because the firearms world is doing all it can to make the AK47 look like an AR-15.

The 7.62x39mm offers a number of advantages, especially since it has much less of an image problem than the the AK47. The 7.62x39mm is a bigger bullet with a solid velocity, and the proper projectile has proven to be a good manstopper. There are no surprises with the round, and it has proven itself for decades in every corner of the world.  Until the recent paranoia, it was prevalent and very economical, manufactured in huge quantities all over the world with mil-surplus ammunition plentiful. Although certainly not a bargain anymore, it is still less money than many of the NATO cartridges.

AR-15 Solution

pws-diablo-762x39mm-bThe CQB compensator, made by PWS, is intended to make the system run more efficiently and provide sufficient backpressure.

The solution is the manufacture of an AR-platform rifle that uses the 7.62x39mm cartridge. It was simpler to envision than to make it reality, especially with the gas impingement systems. There have certainly been more than a few out there starting with Colt many years ago, which still has following to this day. Several other companies are making and have made uppers in that caliber as well. Most of these worked pretty well with the primary issue being the magazines. With a good magazine these rifles worked pretty well, at least as well as any AR-15 did at the time.

The next step in the evolution was to build one in a piston driven platform. It only seems fitting, since most of the piston driven guns out there are some variation of an AK47 action. There have been a few over the years, but the market was just not there and they were never widespread. There was also the ever-recurring issue with the magazine. Even with the problems there were always a few out there clamoring for an AR-15 in 7.62x39mm that worked.

That clamoring has grown as of late and become a more popular idea. Some were asking for a short-barreled upper. The cartridge lends itself to close-up work and seems to lose far less velocity when the barrel is shortened when compared to the 5.56mm. You are still right at 2,000 fps (feet per second) with a 120-grain bullet in a 7-inch barrel. It is just about a perfect weapon for entry, or executive protection. Well, it seems that Primary Weapons Systems has listened, as they now have an SBR Diablo in 7.62x39mm.

Upper Details
pws-2The Picatinny rail forend of the Diablo extends to the muzzle device, offering the longest sight radius possible for the folding iron sights.

Having tested several of their uppers, PWS builds some of the best quality receivers available. The workmanship is first rate, the quality control is solid, and quite frankly I have never had one that did not work. When the Diablo arrived there was no disappointment. The receiver is a VLTOR MUR-1 and mated to the PWS forend nicely. It uses the CQB compensator seen on all Diablo’s receivers. The barrels are stainless steel with a polygonal bore. The bolt is also stainless and a billet machined charging handle is used. To ensure trouble free operation the internals are all coated with QPQ, a super hard coating that not only makes the parts last longer, but has a natural lubricity making them resistant to operational issues due to fouling. The bottom line here is — it is quality and often at a retail price point at or lower than the competition. It is one of the things I really like about this company. The upper comes with one 10-shot C-magazine and enough rail panels to cover the rail as you see fit.

For this test a new buffer tube, tungsten buffer and spring was provided. This was something PWS introduced recently and has become quite the hit. More than just another buffer tube, there is quite a bit of innovation here. It is machined from a solid piece of 7075 aluminum and has six positions. This eliminates the castle nut and places QD sling swivels on the tube. Out of the box, it allows a single-point on either side without anything hanging out to catch your knuckles on. It has the added bonus of allowing the stock to close all the way, something other systems prevented. The tube extends over the retaining pin, making it impossible for it to come loose.

Another innovation is the dead blow buffer installed in the rear of tube to reduce carrier speed. This is critical for a rifle that is suppressed or has a short barrel. The buffer is a Spike’s Tactical machined from solid bar stock and filled with Tungsten instead of weights. It is designed to smooth out the recoil. Coupled with the buffer tube the difference was rather striking.

Range Time
For testing purposes the upper was placed on two lowers. One is an M16A2 lower the other an SBR (short barreled rifle) lower. For the purposes of the test of the buffer, it was tested both before and after the buffer tube was installed. Both of these lowers have proven reliable with numerous different uppers attached.
The first thing you notice is how compact it is. The entire rifle with sling and magazine fit nicely in a 5.11 Select Carry Sling Pack. It was a tight fit but drew easily and did not imprint. The Pack was comfortable and pretty inconspicuous; it looks like the bags cyclists use. This would be about perfect for a covert operation or recon for a SWAT team. That is a ton of firepower to bring to the fight in a covert package. Although the 10-shot magazines were used just for kicks, a 30-shot AR magazine was inserted and it still fit. Even better would be a solid and reliable 20-shot magazine. That would mean less extension and plenty of ammo for most.

The testing began with the AR lower without the buffer tube installed. Given the caliber and barrel length some recoil was expected. There really was very little, less than any AK47 I have fired and no more than a standard piston driven 5.56mm rifle. It was very comfortable to shoot and that CQB flash hider/ brake really does its job. Expecting a huge fireball even in daylight, it was no worse than a standard flash hider.

Muzzle rise was minimal and it was very easy to keep on target. It was loud however, as anyone would expect with a 7-inch barrel. Flashbacks of my days fielding a Micro-Galil with a short barrel were creeping in. In a gunfight you would hope for auditory exclusion or if you can, a suppressor would be nice. That was another surprise. Unlike the short-barreled 5.56mm rifles, my .30 caliber Jet suppressor worked flawlessly. I am guessing any quality suppressor would work as well. This weapon suppressed is a riot to shoot.

The next test was after the installation of the buffer tube and buffer. The installation was incredibly simple and fast. The tube is bulletproof and will not come loose after installation. It is the most solid and well thought out tube that has come along.

Since the PWS uppers come with a means to attach a QD sling to the forend, it allowed me to simply switch my sling from the other guns. The position allows for very solid and secure carry, and you can even use a single-point if you prefer.

After the first couple of rounds, I had to make sure it was firing. The thing just sits there spitting out ammunition as fast as you can pull the trigger. Shooting on the move was incredibly stable, as the dot just stays put. Any movement is from you, not the recoil of the gun.

The tube is Mil-Spec, not the commercial spec, so remember that if you change out the stock. All mil-spec stocks should go right on. I would recommend the tube and buffer conversion regardless of the upper you have, especially if you use a suppressor. When the suppressor was placed on this configuration, it was like shooting an MP5 SD only with a real bullet.

The next move was to the M16A2 lower. This is a bone stock lower and has served for many years. This Diablo is quite controllable on full-auto. Doubles and triples were a cinch. It would be very easy to dial up full-auto and place doubles where needed in a CQB environment. It emptied the 10-shot magazines rather quickly and without a hitch. Luckily they threw in a few of them for the test. Bottom line here, it works well, and would serve any operator on an entry or protection team.

The rifle simply never missed a beat at all — it was flawless. Not one single malfunction over a couple days of shooting. It is pretty accurate as well. Just for kicks I fired from prone at 100 yards from a bag using an Aimpoint. I fired a couple of 3-inch groups using Wolf Military ammunition. I was whacking 8-inch steel at will at that range. Up close and personal, it was as accurate as you get. Keeping shots on the head during CQB was a cinch. It truly reminded me of using an MP5 SD on entry. No recoil, fast reset, and accurate as all get out.

As to the gun, well it is a riot to shoot, works flawlessly, and is very practical for entry or protection work. With this cartridge you do not give up a ton of knockdown power even with a 7-inch barrel. With solid magazines it is a screamer — I would not hesitate a second to put this SBR to work.

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The 7.62x39mm PWS Diablo upper receiver worked well with the author’s registered SBR lower,…