Gun Review: Primary Weapons Systems MK111 MOD 2 AR Pistol

Primary Weapons Systems (PWS) literature clearly lays out the thought process behind the development of its ARs — the appreciation of AK47 simplicity and reliability combined with deep-rooted experience with M4/M16 ergonomics. PWS is confident its long stroke piston operated AR is an improvement over not only the original gas impingement design, especially when incorporated into short barrel platforms, but also other piston AR designs featuring short stroke pistons. A look at a PWS MK111 AR pistol disassembled with the AK-like operating rod connected through the charging handle to the bolt carrier leaves little doubt of the AK inspired PWS design.

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The increasing use of suppressors for civilians, law enforcement, and military highlight another advantage of the piston-driven ARs — the ability to adjust the amount of gas siphoned to operate the action. Suppressor use increases operating pressures a considerable amount and ability to quickly turn a knob turning down the gas vented to the operating rod is a big advantage. Currently, piston driven ARs also enjoy a perception of better operating reliability in harsh environments, especially as barrel lengths shrink. The Primary Weapons Systems PWS MK1 series represents cutting-edge long-stroke AR pistol design.

Continued Evolution

With all of this stated, PWS continues to evolve its design. The latest PWS has to offer is their MK111 MOD 2 .300BLK upper mounted on PWS pistol lower. The MK111 weighs in at 6 lbs. An 11.85″ stainless Isonite treated barrel with threaded flash hider gives an overall length of 28.4″. The MK111 long stroke piston operation helps to smooth out recoil impulse especially when combined with other PWS features. PWS created a forward canted “dwell” chamber in front of the operating piston’s head. This compares favorably to more typical horizontal or rearward angles associated with gas vectoring. The forward cant also helps to minimize carbon build up on the operating rod.

A new feature on the MK111 MOD 2 is the PicMod rail. This allows you to use KeyMod attachments while still being able to mount most Picatinny accessories directly to the rail in the areas where the PicMod feature is present. The PWS rail system permits the barrel to be free floated.

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PWS uses forged upper and lower receivers allowing for a stronger and lighter product. PWS takes the stance that proper forging creates continuously aligned grains throughout the part creating a stronger, yet lighter, receiver. A “hidden” enhancing feature with the MOD 2 is the Enhanced Buffer Tube (EBT). The new PWS EBT is impact extruded from 7075 to enhance strength and rigidity, and mil-spec anodized. An extended lip on the buffer tube serves to eliminate carrier tilt. An extended BCM charging handle offers the user plenty of purchase to operate the MK111’s bolt group.

ar pistol, PWS, mk111, new guns, gun
PWS MK111 MOD 2 pistol chambered in 300BLK. Ammunition availability —both in terms of subsonic and supersonic loadings — has made the .300BLK one of the most popular AR15 chamberings.

A PWS provided tool stored in the pistol grip inserts into the adjustment holes in the gas knob and you simply rotate it to the next position/detent until the desired setting is selected for your specific suppressor set up. An adverse condition setting is not needed as the PWS system is designed to operate with enough back pressure at all times no matter how dirty or fouled — this is something to be appreciated in a fighting rifle. The .300BLK chambered PWS rifles are even simple — no adjustment needed. PWS research and product development with the .300BLK has shown it does not need the gas adjustment system as found on .223/5.56 rifles and pistols. The .300BLK MK111 AR pistol is meant to run with a can or without, with supersonic or subsonic ammunition with no gas adjustment required.

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The long stroke piston PWS AR has its operating rod connected directly to the bolt carrier group.

300 Blackout

What distinguishes the .300BLK is the ability to access standard supersonic rounds for typical longer-range engagements superior to 5.56mm while maintaining trump card of subsonic ammunition for more discrete specialized work. The .300BLK was created in response to a US special operation military forces’ request. Literature illuminates their goal with the .300BLK as being the ability to launch .30 caliber projectiles from the AR platform from existing 5.56 magazines without a reduction in magazine capacity or reliable functioning.

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.300BLK cartridge between two 5.56mm rounds.

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Another notable characteristic of the .300BLK is its compatibility with the AR standard bolt — making only a barrel change is necessary. At 300 meters, the .300BLK has approximately 17-percent more energy than the 7.62×39. The .300BLK from a 9″ barrel has the same energy at the muzzle as a 14.5″ barrel 5.56 M4 and surpasses it as ranges extend.

Hornady, SIG SAUER, and Black Hills .300BLK loads were chronographed. The supersonic loads clocked between 2,110 and 2,295 fps from the PWS 11.85” barrel with the subsonic loads measuring 890-925 fps. Accuracy from the .300BLK barrel was a pleasant surprise. No load tested, whether supersonic or subsonic, produced greater than 1.75″ average accuracy at 100 yards after firing three 5-round groups.

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SIG SAUER SRD 762 suppressor adapted easily to the PWS MK111 via SIG SAUER Taper-Lok Fast-Attach System.


A SIG SAUER Romeo 4T red dot enhanced with SIG SAUER Juliet 3x magnifier was used with the PWS MK111 AR pistol. The Juliet magnifier was on a tilt mount allowing for it to be swung out of the way until deployed. The Romeo 4T proved ideal in the Echo Valley Training Center’s (EVTC) Hesco Shoot House. The CQB format helped to highlight the potential of the .300BLK PWS MK111, especially when suppressed. For law enforcement, military, civilian or private security contractor the SIG Romeo red dot Juliet magnifier combination is worthy of consideration as it enhances rifle performance.

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SIG SAUER ROMEO 4T red dot and SIG SAUER Juliet 3X magnifier an ideal set up for an AR pistol. The Juliet magnifier tilts out of the way until needed.

Over 350 rounds of subsonic and supersonic ammunition were fired through the PWS MK111 pistol. The .300BLK subsonic loads had no issue cycling the rifle, even when firing without a suppressor attached. Not every .300BLK platform on the market shares this characteristic. The advantage of having a .300BLK weapon like the PWS MK111 functioning with subsonic loads unsuppressed means a user can be confident of a functioning weapon no matter ammunition in use.

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A compact weapon like the PWS MK111 AR pistol has its own advantages in terms of handling, ease of concealability and increased portability that is hard to resist. What does the AR pistol offer in terms of real utility in its pistol form?  The answer here is nebulous based on user expectations and method of use. The fact the AR pistol is classified legally as a handgun offers users who have a concealed carry license a certain amount of flexibility compared to a true rifle or NFA classified weapon. We are talking about carry options based on handgun label. Here is where the AR pistol’s true asset in one’s inventory becomes evident.


  • Weight – 5lb 13.4 oz
  • Barrel Length – 11.85″
  • Overall Length – 28.4″
  • Gas Piston System – Carbine
  • Barrel Twist – 1:8

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