Primary Weapons Systems builds some of the most reliable AR rifles you can buy in my opinion. Using a modified gas piston system, the company’s rifles are softer shooting, cooler to run and simpler to maintain. Having previously tested PWS’ rifles in both 5.56mm and 7.62mm, I thought it was time for 300 BLK. The 300 BLK round is low pressure by comparison, making gas tappet piston guns problematic. Pistol-length direct impingement versions are the norm and work great with short barrels, but I wanted something in the middle and the PWS MK112 with a 12.75-inch barrel seemed just about perfect.

After years of using and testing ARs, a 12.5- to 13-inch barrel has proven the most versatile. While short enough for entry work, this barrel length retains ballistic efficiency. While shorter barrels are common, it limits the range in a caliber well suited to 300-meter distances. My hunch was that a 13-inch barrel would keep it handy with little velocity loss. I ordered a PWS MK112 to mate to my registered PWS MK1 lower and see if my theory was correct.

Hard Charger

My registered MK1 lower uses a Geissele Super Dynamic Combat trigger and an ambidextrous, 60-degree safety from Battle Arms Development. The grip is from Bravo Company and the stock is from Vltor. The addition of Law Tactical’s Gen 3 folding stock makes for a truly compact rifle; PWS bolt carriers just need a different extension and Law Tactical has them. Installation is simple, allowing this rifle to fit my Eberelestock packs along with several other covert carry systems.

The upper uses a forged receiver and features a slim, KeyMod-equipped rail. A QPQ-coated, 12.75-inch barrel with a profile designed to lose weight, not accuracy, is installed. Chambered in 300 BLK and featuring a 1-in-8-inch twist, it is button rifled using M4 cuts for proper feeding. Isonite coating is becoming the standard for any hard-use AR. Set up for use outside the range, a Triad flash suppressor was also installed.

PWS bolt carriers and bolts are made from tool steel, which exceeds military specifications, and are then nickel Teflon coated for reliability and ease of maintenance. Designed specifically to work with PWS rifles, these units are some of the most advanced on the market and as strong as can be made.

Trijicon’s VCOG 1-6×24-power scope has proven to be a favorite of mine when simple and rugged reliability is needed. Its segmented circle reticle configured for the 300 BLK makes it about perfect for any distance. Trijicon’s RMR was added at the 1 o’clock position. The VCOG performs well or better than any scope up close, but my personal preference remains offset irons and/or an MRDS when close-quarters distances are in order.

First Hits

Early testing revolved around my existing inventory of ammunition along with Barnes’ new 120-grain TAC-X bullet. While the 110 grain has been popular, the 120 grain should prove a better choice if you are going to longer distances. Terminal ballistics on this bullet have become almost legendary, and this new version looks to be about perfect for my needs.

Accuracy with the PWS MK112 was excellent with the Barnes load, producing a 0.75-inch group at 100 yards. Fired from prone using my pack as a rest, this is about as accurate as it gets for me. Everything else tested under 1.5 inches. Shooting off-hand at 25 yards, the 120-grain Barnes stayed inside 2 inches, making it more than precise enough for the real world. Compared to 16-inch barrels, the measured velocity proved to be almost identical, with the largest difference being less than 25 feet per second (fps). My hunch was confirmed.

Testing at this point was confined to unsuppressed fire, and the PWS performed incredibly well. Ammunition ranged from a 147-grain practice load to a 125-grain match, along with some of my hand-loaded practice rounds using once-fired and converted .223 brass and short projectiles. With a Sprinco Blue extended- power buffer spring, it ran it all but failed to lock open on the handloads on occasion. Switching to the standard Sprinco White spring eliminated that with no further malfunctions. Primary Weapon Systems’ H2 buffer was also used during. Currently, the company’s enhanced buffer tube will not work with the Law Tactical folder, so
it was replaced with a mil-spec tube.

After Action Report

Moving out to longer ranges is where the VCOG really shines. After zeroing at 100 yards, 6-inch steel was engaged at 200, 300 and 400 meters. Accounting for wind, it was dead on and yielded consistent hits on steel. This reticle includes aiming points for 220-grain subsonic that will be tested a bit down the road, but for now it has proven to be accurate with 110- to 125-grain bullets with little change in holds out to 350 meters.

This rifle will see some more testing in the next few months, but preliminary results proved to be excellent. The MK112 is one of the softest shooting 300 BLK rifles I’ve used to date. Accuracy was excellent and reliability was superb, keeping it in line with every other PWS rifle I’ve tested so far.

Primary Weapons Systems is well known for thinking outside the box. The entire company is built around the concept of doing what works, and this is reflected in most everything it makes. Built with reliability, function and purpose in mind, PWS rifles remain simple, easy to maintain and reliable. The company brings that process to everything it makes, including its Glock slides, precision rifles and components. In a sea of choices for an AR rifle, the PWS MK112 stands out as one of the most reliable and useful piston-driven rifles you can buy.

Primary Weapons Systems MK112 300 BLK Specs

Caliber: .300 BLK
Barrel: 12.75 inches
OA Length: 29.5 inches
Weight: 6.37 pounds (empty)
Stock: Magpul MOE
Sights: Magpul MBUS
Action: Piston-driven semi-auto
Finish: Matte black
Capacity: 30+1
MSRP: $1,950

Primary Weapons Systems MK112 300 BLK Performance

Load Velocity Accuracy
Barnes Vortex 120 TAC-XP 2,100 0.75
PNW 125 Match 2,200 1.00
PNW 147 Practice 1,900 1.60
Remington 125 OTM 2,250 0.80

*Bullet weight measured in grains, velocity in fps by chronograph and accuracy in inches for best 5-shot groups at 100 yards.

For more information, visit

This article was originally published in the 2016 issue of “Black Guns.” To order a copy, visit

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