On Target Review—Primary Weapons System MK114 Rifle

Primary Weapons System MK114 upper. Comes with Magpul BUIS.
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By Rob Kay and RN Price

Primary Weapons System MK114 upper. (Comes with Magpul BUIS). We added a Trijicon T31F, Blackhawk Sling and Blackhawk Rail Mount Sling Adapter for the review.

By now everyone has heard of the advantages of a Gas Piston system vs. Direct Impingement many times over.


With a piston gun you don’t have to run the bolt wet and you can adjust the gas setting, which comes in handy when running a suppressor. (Of course in Hawaii we can’t own a suppressor but I digress). Of course, cleaning a piston gun is a walk in the park compared with scraping carbon off the bolt carrier of a DI rifle.

When we showed up at the range a few weeks ago with our Primary Weapons Systems (aka PWS) MK114 upper, as if on cue, the guy at the station next to us had exactly the same gun laying on his bench. Of course we couldn’t help but ask how he liked it. The first thing to come out of his mouth was “It’s so easy clean!”. He said incredulously, as if this were too good to be true “It only takes a few minutes for me to clean this rifle!” Another happy camper and surely, a convert to the gas piston club.

Of course there’s always two sides to a story.

The rap on gas piston jobs is that they aren’t as accurate as DI guns, they aren’t as dependable (they break down more often), they are heavier, they’re not as well balanced and on average, they are more expensive. All of the above may have been true at one point but, based on what I experienced with PWS, the landscape is rapidly changing.

Of course is the part about piston guns being more expensive hasn’t changed. They are still more expensive. Sometimes by a factor of two.  Another point that DI enthusiasts bring up is that all gas piston guns are proprietary. If a part breaks, they may be hard to get. (Especially if the manufacturer goes out of business).

The MK114 has an understated air of quality.

That said, piston technology is surely getting better and PWS is a poster child for this evolving genre.

As with all gas jobs, the PWS has a proprietary technology. Designed in the spirit of the AK-47, it has a long stroke, fixed operating rod linked to the carrier and a floating head piston assembly.

PWS believes it marries the best of both worlds, the drop dead accuracy and ergonomics of an AR with the reliability of an AK 47. The MK114 also sports a 14.5”free-floated barrel barrel (chambered in Wylde) with a 1:8 twist, the obligatory adjustable gas block, a Magpul BUIS and a 13” hand guard. A QD swivel socket is available right in front of the receiver before the first keymod slot.

PWS states that all parts manufactured  on state of the art CNC Machines such as Okuma Multus B300 lathes, HAAS VF-4 mills and others. The guys that operate the machines are also shooters. 

The Wylde chambering aka “223 Wylde” is a hybrid meant to combine the accuracy of a .223 with the reliability of 5.56. In theory it allows you to shoot both .223 and 5.56 rounds accurately. It’s been showing up as an option on premium rifle manufacturers over the last couple of years.

Both the barrel and the BCG are “isonite” coated. The website for Trutec, a company that offers this product explains that isonite is a “thermo chemical diffusion process whereby nitrogen-bearing salts generate a controlled release of nitrogen at the interface of a ferrous part.” (If someone can translate this into English we would be quite happy). The website says the treatment is “better than chrome plating” and offers improved durability, corrosion resistance, low material distortion, greater resistance to abrasion and seizure, and is pleasing to the eye to boot. (We’ll have to assume that PWS did it’s homework in this department.)

The FSC556 compensator is top notch

Speaking of pleasing to the eye, one of the things we really liked about the PWS MK114 was its aesthetics. 

This is an adult gun with grownup sensibilities. There’s nothing fancy about the upper but it has a refined, almost understated appearance. There are no silly zombie logos or other middle school jimcrackery. It may need a scope or a sling but it’s not going to need a “makeover”.

All the components including the barrel (manufactured by Bergara in Spain) , the BCM Gunfighter Enhanced Charging Handle and the permanently attached FSC556 flash hider/compensator reek of quality. (The FSC556, btw extends the length of the barrel out to 16, legal inches). It does a good job of keeping the rifle steady and reduces muzzle flip which makes follow up shots easier to manage.

We can’t speak for other gas piston guns but we can categorically state that the MK 114 was dead on accurate right out of the box.

The upper was well balanced, light and a joy to shoot. We we able to manage approximately 1 inch groups from the get-go at 100 yards with mediocre ammo. It was hardly a scientific accuracy test but it did suggest that this was a a consistently accurate upper. We suspect with a bit more discipline at the bench and some decent hand loads tweaked for this rifle, we could have done much better. PWS says the barrel is match grade and I don’t doubt it.

Long range accuracy is a big deal for us and we wanted to push this upper as far downrange as we possibly could. At Koko Head that means 455 yards. The second time out we were hitting the 455 yard plate. Not as consistently as we would have liked but given that it was windy (of course it’s always windy at Koko Head!) and we had off the shelf (cheap) ammo hitting that gong was a minor feat. PWS recommends going to the heavier bullets to take advantage of the 1:8 twist.

We used 55 gn American Eagle for this group. With a better load we could have tightened things up.  Manufacturer recommends 77 gn Blackhills ammo.

Stacey Nagy, a spokesman for PWS, says that ballistic performance wise, there is “very little difference” between the 14.5”, 16” and even 18” barrels. He is partial to the MK114 which he calls a “do everything” barrel. “It is short enough”, says Nagy, “for many scenarios that might require a SBR but does not limit the user to a 0 to 300 yrd max effective range as a 10.5 inch barrel length can.”

Operating the upper was dependable. There was a jam or two the first time out but given that the upper was really tight, this is was reasonable to expect.  After the initial break in, there were no jams.

Cleaning the upper, as our range-mate alluded to at the beginning of this article, was indeed really easy. (PWS put together a nice little video that demonstrates the cleaning process and is worth watching). Essentially you just drop the BCG/charging handle out of the back end of the receiver and clean out the barrel, wipe down the piston and swab out the gas cylinder. That’s pretty much it. After a session we found the BCG spotless. For those used to going through the drudgery of a DI gun, at the end of the day owning a MK114 will definitely be a breath of fresh air.

Idaho, where PWS is located, is a far cry from Moililili where you’ll find Gun Source, the local dealer who sells the brand here in Hawaii. Tony Lee, the owner of Gun Source, said he heard about PWS from a returning Iraq veteran who walked into his store and sung its praises. Tony ordered one and after seeing up close and personal, decided to become the dealer. In about two and a half years he has sold over 400 rifles.

Out of all those sales Lee says only two rifles had “issues”. One kept on jamming, but that problem was resolved after the customer stopped using junk ammo from South Africa.  (For the best groups, PWS recommends 77 gn Blackhills match ammo brand ammo, which is fine if you can get it).The other issue that Lee reported on the PWS gun was a broken link that connected the piston and the piston rod. (This was on an earlier model, not the current series). He said the part was quickly replaced and that ended the story.

Like all piston guns, PWS guns don’t come cheap. As the adage goes, you get what you pay for.

The BCG assembly (at foreground), which includes the piston rod,  and charging handle is easy to remove and a dream to clean.
You’ll pay $1949 for the rifle and can buy the upper for around $1300 for the upper. I would seriously consider their version with the 16″ barrel which provides a bit more velocity.  (PWS also manufactures a “MK2” series in .308).
In addition to the MK114, with the aforementioned 14.5” barrel, you can get the “MK 1” series in a 16” or 18” barrel (MK116 amd MK118). 
After spending a great deal of time with this piston gun, we’re sold on the whole concept. I don’t think there’s any doubt that the era of the gas piston AR is upon us and it’s time to embrace it. If you’re ready to try, you won’t go wrong with a PWS.

All photos by On Target Hawaii Staff. 

Questions?  Comments?  Contact us at ontargethawaii@gmail.com

Rob Kay writes about firearms for Hawaii Reporter and is the author of How to Buy an AK-47.
Read more of Rob’s articles on OnTargetHawaii.com





  1. Well, Manjo, when they come home from army, army gives them all their equipment. Their prime minister was asked once "What would Switzerland do if its invaded?" And the prime minister said: "Everybody will shoot two times and then they'll go home." This is what they are: a natural fortress and an armed country.

  2. That is a very powerful weapon! I don't think it's a good idea for people to start buying such weapons for their personal use. This is a bit over the top!

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