Want to upgrade to a piston AR? We review PWS' most popular long stroke piston upper (MK116 Mod 2-M) for reliability, shootability, accuracy, and more.
Ready to move up to a piston AR-15?
I review one of the most popular models out there…Primary Weapon System‘s MK116 Mod-2M which might be everything you ever wanted.
PWS MK116 Mod 2-M Upper
By the end you’ll know a little more about piston ARs…and how the MK116 Mod 2-M shoots, its accuracy, and whether it’s worth the upgrade price.
Someone who wants to have a cleaner & cooler shooting AR system (especially when suppressed)
Someone who wants a long stroke piston vs a short stroke piston upper
Long Stroke Piston FAQ
You probably know the basics of piston vs direct impingement (regular ARs).
Direct Inpingement Gif
In direct impingement (DI) systems, the gas is routed via the gas block to the bolt carrier which then moves back with the force. However…this gets all the exhaust gas and powder into your gun.
With a piston system…the gas moves a piston which moves the bolt carrier. Therefore only a small area of the piston itself gets dirty.
PWS Long Piston System
Now…there’s different flavors of piston.
First up is the short stroke piston which is where the piston is separated from the bolt carrier. It’s lighter…but with more parts and could be more susceptible to “carrier tilt.”
Adams Arms P-Series Piston Kit
However it’s generally the more popular option since you can retrofit a normal AR into a short stroke piston.
With a long stroke piston…the piston and bolt carrier are one.
PWS MK116 Long Stroke Piston
It’s heavier in weight and recoil…but there’s less moving parts. Other famous guns that use a long stroke include the AK-47 and M1 Garand.
If you’re going for best possible reliability I’m going to hand it to the long stroke. But if lightness and slightly less recoil is the name of the game…go with a short stroke. Read more about this at The Truth About Guns.
Fit & Feel
PWS was kind enough to send me their MK116 Mod 2-M upper for testing.
PWS MK116 Mod 2-M Upper, Other Side
It’s their best selling option and meets all my normal criteria for an upper:
Finish was immaculate and what I expect if I’m shelling out over $1000 for an upper by itself.
Plus I love the extra design details on the upper receiver.
PWS MK116 Upper Receiver
There’s no forward assist so if you’re in that camp…too bad.
I quickly added on some fun stuff…
PWS MK116 Mod 2-M with Goodies
One cool thing about the newest versions of the MK116 is that they come with PicLok free-float handguards which…you guessed it…combine both Picatinny and M-LOK.
The top rail is regular Picatinny…
PWS MK116 Front Rail
While the other three sides are PicLok.
PWS PicLock Handguard Attachment
I also went with their 5.56 FSC Compensator…whose design has worked wonders on my AK.
PWS MK116 Side Rail and FSC556 Compensator
And you’ve already seen the long stroke piston design.  But here’s the BCG again…you can see it’s connected to the piston.
PWS MK116 BCG and Piston
Note that because it’s connected…it’s slightly more of a pain to remove the BCG and charging handle (which is a Radian ambi by the way).
Not that you’ll be doing that very often since I couldn’t find much trace of any blowback on the BCG when I took the rifle apart for photos. Just oil ended up on my fingers…and this was after ~400 rounds.
There’s also an adjustable gas system that lets you choose between off, regular, and suppresseduse.
PWS MK116 Adjustable Gas System
I really wish I could get a suppressor to test it out since that’s where it would really shine. With suppressors there’s even more blowback that gets into your breech (and sometimes your face).
A piston does wonders to clean it up.
Now…how does it shoot?
Shootability
A piston gun is going to weigh a little more because you’re adding stuff to the front of the gun.
If you’re getting a piston gun…it’s likely you’re already going to have some stuff in the front. So get ready for a little heft.
SureFire M600 Scout with Steiner DBAL-A3
But remember it’s a trade-off for reliability, cleanliness, and coolness (the temperature kind).
Here’s me shooting it with the muzzle brake for our Night Vision review.
And because there’s a pretty large piston moving back and forth…there’s going to be increased recoil.
I’d chalk it up to be about 50% more than a normal AR-15 with similar specs.
But once you get used to it…still easy to nail plates at 100 yards standing.
Accuracy
After ~200 rounds of break-in I loaded up my standard AR testing platform.
PWS MK116 Mod 2-M Testing
Put the target out to 100 yards. And shot at a leisurely pace of a round every few seconds. Let the barrel cool to warm between each string.
PWS MK116 Mod 2-M Groups
Since there’s more moving parts on a piston upper…you’re likely never going to attain the accuracy from a regular DI system.
The results were bittersweet…
On one hand they weren’t the greatest even for the match Gold Medal rounds. But the good thing was that my cheapest plinking ammo Wolf Gold fared the best at a little over 1 MOA.
Specifications
Caliber: .223 Wylde
Weight: 4 lb. 8 oz.
Length: 25″
Piston System: Mid-length
Velocity: 2980 ft/sec
PWS long stroke piston operating system
3-setting adjustable gas system
Forged upper receiver
Eliminated forward assist
FSC556 compensator
PicLok free float handguard
1:8 barrel twist rate
Radian Raptor Charging Handle
By The Numbers
Reliability: 5/5
Nothing close to a failure in 400 rounds. Plus almost no residue on the BCG.
Accuracy: 4/5
Not sub-MOA but if you’re going piston you can’t expect that for all types of ammo. Good thing for me is that it shot the best with the cheapest ammo!
Ergonomics: 5/5
Really liked the PicLok rail where you can attach almost anything out there.
Looks: 5/5
Will turn heads with the styled upper receiver and different handguard.
Customization: 5/5
It’s an AR-15 with PicLok so you can do almost anything you want.
Bang for the Buck: 3.5/5
On the pricey side for an upper at around $1200. But as far as I know it’s the only long stroke piston AR out there.
Overall Rating: 4/5
Conclusion
It was great fun to shoot the PWS MK116 Mod 2-M upper.
PWS MK116 Mod 2-M Upper
And I’d wholly recommend it if you were going suppressed or want a shorter pistol/SBR length (see all lengths)…since shorter DI systems are finicky. Or if you just want an upper-tier piston gun.
What do you think of the PWS MK116 Mod 2-M? Are you a fan of long stroke or short stroke piston? Check out our other favorites in Best AR-15 Piston Uppers and Conversion Kits.
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5
Leave a Reply
Sidekick501
It’s a nice gun but it’s definitely heavy on the front end. You probably don’t want to be running and gunning with it for a long period of time (unless you’re prepared for a serious upper body workout).
April 4, 2022 4:52 pm
Mike
Lmao!! So let's take one of the best d.i. ar's the daniel defense ddm4v7. It has a totall weight of 6.2 pounds with an upper that weighs 4.0 pounds. The pws mk116 mod 2 weighs 6.5 pounds with an upper weight of 4.8 pounds. So you are saying that 8 ounces is a "serious upper body workout"!?!? ROFLMAO!!!! Bro no offense but you need to spend at least a little time in the weight room if 8 ounces to you is a "serious upper body workout". A Streamlight TLR1HL is over 800% heavier by its self then the pws upper is compared to the ddm4v7. SMH.
July 30, 2022 10:50 am
Mike
**idk how the how the hell my copy and paste did that but I don't like editing original comments so I'm doing a correction.
It should of said a tlr1hl is .508% the weight by itself of the difference between pws vs ddm4v7
July 30, 2022 10:59 am
Alex
How could you say an opinion so wro g about the recoil of this weapon? You said it has 50% more recoil than direct impingement. If I read that without already owning one of these weapons, that would be a reason for me not to purchase it. You have made a completely false and not accurate assessment of this weapon. This weapon shoots with 50% less recoil than direct impingement. Please consider your opinions more wisely before you write your reviews because you could make people who don't know any better make the wrong decisions. This is honestly the best platform I've ever had the pleasure to shoot from.
August 28, 2020 8:20 pm
John Spies
Totally agree. PWS makes a fantastic rifle in many calibers; for the money, I don't think someone could do better. I have no financial interest in the company other than owning 5 of their weapons.
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5 Leave a Reply
It’s a nice gun but it’s definitely heavy on the front end. You probably don’t want to be running and gunning with it for a long period of time (unless you’re prepared for a serious upper body workout).
Lmao!! So let's take one of the best d.i. ar's the daniel defense ddm4v7. It has a totall weight of 6.2 pounds with an upper that weighs 4.0 pounds. The pws mk116 mod 2 weighs 6.5 pounds with an upper weight of 4.8 pounds. So you are saying that 8 ounces is a "serious upper body workout"!?!? ROFLMAO!!!! Bro no offense but you need to spend at least a little time in the weight room if 8 ounces to you is a "serious upper body workout". A Streamlight TLR1HL is over 800% heavier by its self then the pws upper is compared to the ddm4v7. SMH.
**idk how the how the hell my copy and paste did that but I don't like editing original comments so I'm doing a correction.
It should of said a tlr1hl is .508% the weight by itself of the difference between pws vs ddm4v7
How could you say an opinion so wro g about the recoil of this weapon? You said it has 50% more recoil than direct impingement. If I read that without already owning one of these weapons, that would be a reason for me not to purchase it. You have made a completely false and not accurate assessment of this weapon. This weapon shoots with 50% less recoil than direct impingement. Please consider your opinions more wisely before you write your reviews because you could make people who don't know any better make the wrong decisions. This is honestly the best platform I've ever had the pleasure to shoot from.
Totally agree. PWS makes a fantastic rifle in many calibers; for the money, I don't think someone could do better. I have no financial interest in the company other than owning 5 of their weapons.