PWS MK107 Diablo ar pistol, drum magazine
(Photo by Mitch Hardin)

So, who doesn’t love a fire-breathing demon at your fingertips, really? Especially when it’s a demon that you can grab by the horns, and take for a ride. Primary Weapons Systems calls its PWS MK107 MOD 2-M Pistol the “Diablo” for a reason. More on that in just a bit.

PWS is the American Dream. It started in a garage by owner and designer Dean Sylvester. At the time, Sylvester designed and made brakes and other related AK-47 parts. Then he had a revolutionary idea: Adapt the gas piston system of the ultra-reliable, battle proven AKM (AK-47) so it works on the AR-15. Thus, we now have an AR-15 with a three-position long-stroke gas piston operated system.

If you get lazy, you can even clean it about as often as you clean an AK … seriously. I’ve heard of a PWS MK116 with just more than 5,000 rounds down range with no cleaning, for endurance testing. Sounds about right, as I personally know of an AK with a higher round count and no cleaning, and it’s still going strong. I really don’t suggest it, but it is doable. The Paratrooper in me won’t allow any weapon I own to stay dirty for long. Proper weapons maintenance was beaten into us early on.

The Demonically Wonderful PWS MK107 Diablo

PWS originally designed the MK107 MOD 2-M “Diablo” AR Pistol as an alternative to the 9mm H&K MP5. The Diablo offers 5.56mm solutions out of a 7.75-inch nitrided barrel, while producing unquestionable reliability. One cannot ask for much more than that.

Taming the demon is the CQB Compensator, also designed and made by PWS. It literally makes follow-up shots that easy, even from a barrel this short. To help with accuracy, PWS uses a .223 Wylde barrel with a 1:8 twist; this allows the user to shoot both 5.56 and .223 Rem. with greater accuracy potential.

ar pistol 5.56/223, right, Primary Weapons Systems Diablo
(Photo by Mitch Hardin)

Both the upper and lower receivers are T6 7075 Forged aluminum. The MOD 2-M lowers are fully ambidextrous as well, which is great for us southpaws. Having an ambi lower for this project was a must. You can shoot strong and weak handed, as well as if you are wounded and only have one hand in the fight.

PWS chose a 6.9-inch handguard for the MK107 MOD 2-M. A very cool feature unique to PWS is the way it attach accessories. PWS came up with its own system called PicLok. It incorporates MLOK with a Picatinny rail, so one can utilize both.

Also, factory is the Radian Raptor ambidextrous charging handle. It’s my personal favorite charging handle, as it works great, doesn’t snag on equipment, and is easy to manipulate with either hand.

Other Additions

While the MK107 comes with a nice enough mil-spec trigger, I like to make things truly “mine.” Plus, I have come to really like some of the triggers offered from RISE Armament. This Diablo got the newer RISE “Blitz” single-stage drop-in trigger. It comes with anti-walk pins and a 3- to 3.5-pound pull. When RISE Armament says that it’s got an “icicle like” break, it isn’t kidding. It’s got a very crisp break.

The other addition to the MK107 was the Law Tactical Folding Brace Adapter. By adding a folder, the storage options just increased. One can stow it under a seat, in-between seats, or in some cases, even behind the seat. Think about it though, now you have the perfect “truck gun” that is your own personal fire-breathing pet demon. I’ve used Law’s folders on several builds and haven’t had an issue yet. They are the best thing going for a folding brace/stock option in my opinion.

PWS MK107 Diablo ar pistol, folding stock
(Photo by Mitch Hardin)

SB Tactical sure needs no introduction, as they are the leaders in pistol braces that actually work as advertised. No modifications needed—imagine that! The SBA3 Pistol Brace is right at home on this little beast.

Optic Upgrade

While ordering another scope mount from American Defense Manufacturing, I noticed that it got into the red dot business. ADM now offers its very own dot called the SPEK. It has 10 daytime settings and three night vision settings. It also uses a commonly available AAA battery for power. I’ve been playing with it for a few months now and really like it. The battery is rated at five years, which is really nice. The SPEK comes with an ADM Titanium QD Mount that will grip a rail like a vice.

Interestingly enough, ADM also offers a 3X and 5X magnifiers called the FLIK. It pairs right up with the SPEK, but just wasn’t applicable for a build like this. If you can’t hit your target within 50 yards with a 7.75-inch barrel and a 1x power red dot, then you just might want to make peace with God, because you’re probably about to be sent on your way to meet him.

Range Time With the PWS MK107 Diablo

Good times! The PWS MK107 MOD 2-M is so much fun! Thanks to the soft-shooting PWS long stroke gas piston system, and its CQB Compensator, follow-up shots were easy enough to obtain. It’s a very accurate AR Pistol as well. At 50 yards I netted a 0.9-inch group using Hornady Critical Defense .223 Rem. 73gr. FTX. It also came screaming out of the business end of the barrel at 2,137 FPS.

I used a variety of magazines to check fit and function. There are no issues to report; everything worked exactly as intended. Out of approximately 500 rounds fired, I also had zero stoppages. Another surprising tidbit: The chamber wasn’t even that dirty. That’s hard to imagine for a barrel this short, so chalk it up to the long-stroke gas piston system that is the heart of every PWS AR.

PWS MK107 Diablo ar pistol, left
(Photo by Mitch Hardin)

It’s hard to find fault in a PWS AR. Then again, I was blessed to be given a tour of Primary Weapons Systems and saw firsthand how it designs and manufactures its products. If I had to say something negative, I’d say that it should have incorporated a sling swivel socket on each side of the Diablo’s handguard. That’s about all the negative I can find with this AR Pistol, if you could even call it a negative.

Final Thoughts

The PWS MK107 Mod 2-M is an exceptional truck gun, or personal defense gun in general. For home defense though, I’d invest in a sound suppressor so the whole family isn’t learning sign language after a burglary “attempt.”

Overall, it’s a great little AR Pistol. If you had one placed into your hands, you would probably want to take it home. Every trigger pull brought a smile, as the recoil impulse is very minimal. Couple that with the legendary reliability of Primary Weapons Systems, and you have a winner for sure. For even more info, please visit

PWS MK107 MOD 2-M “Diablo” Specs

  • Caliber: .223 Wylde
  • Barrel Length: 7.75 inches
  • Barrel Twist 1:8
  • Weight: 7.2 pounds (as equipped in article)
  • Optic and Mount: American Defense Machining SPEK with Aluminum QD mount ($369.99)
  • Trigger: Rise Armament BLITZ Drop-In Trigger ($199)
  • MSRP: $2,099.95
  • Complete Package: $2,668.94

PWS MK107 MOD 2-M “Diablo” Performance

Federal American Eagle .223 Rem. 55gr. FMJBT2,1771.1 / 3.2 inches
Federal American Eagle .223 Rem. 62gr. FMJBT2,1591.6 / 3.7 inches
American Eagle .223 Rem. 75gr. TMJ 1,8831.1 / 2 inches
Speer LE Gold Dot Soft Point.223 75gr. GDSP1,9461.4 / 1.8 inches
Frontier (Hornady) .223 Rem. 55gr. HP Match2,2912 / 2.1 inches
Hornady Critical Defense .223 Rem. 73gr. FTX 2,1370.9 / 1.3 inches

Bullet weight measured in grains, velocity in FPS by Caldwell G2 Ballistic Precision Chronograph at 5 feet, and accuracy in inches for best five-shot groupings at 36 and 75 yards from standing modified support, using a Kopfjager K800 CF with Reaper Grip .

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