Primary Weapon Systems MK116 Upper - Review

[boss_hawg]

This is part 1 of ? featuring my very amateurish review of the Primary Weapon Systems (PWS) MK116 Mod 1 upper. I will be updating periodically as I intend this to be a very in-depth, multi-session review. I hope to push the upper with extensive use over the next several months.


First, what is it?

This is an AR-15 upper featuring a QPQ finished barrel in 223 Wylde chambering with a 1x8 twist. The barrel is 16" long, threaded 1/2x28, and uses a carbine length piston system (much more on this later). The upper appears to be standard mil-spec with the very cool PWS logo right above the charging handle insert.

It includes a forward assist and dust cover. Other models such as the MK107, 110, and 112 are designated based on barrel length (the 107 is 7", 110 is 10", 112 is 12" and so forth). Not all calibers are available in all lengths. For instance, the 12" model 112 is 762x39 and 300 BLK only.



Upper is shown attached to my RRA lower, built out with a Daniel Defense LPK, CMC Trigger, Magpul OD Green SL Grip and SL-K Stock. The optic is a Nikon P223 1.5-4x. This will be my test setup unless I decide to - in the future - move to my YHM/Geissele SD3G or Spike's Tactical/Milspec tigger setups.

The upper ships with a 15" PWS keymod rail system with full-length picatinny at 12 o' clock and keymod at 3, 6, 9. It also includes 2 five-slot keymod to picatinny rail attachments. I immediately took these off, though I reinstalled them in the picture above to provide an attachment point for a bipod (helps in sighting in the scope). The rail itself is very light and locks up well to the receiver. Six set screws secure the rail to the upper - two each at 3, 6, and 9 o' clock. For reasons discussed later, I had to remove the hand guard. It was easy enough and reinstall was a breeze. These hand guards sell for $200 plus on their website for installation on a non-PWS setup. They (or it?) are very nice.

Also, before we dive into the unique semi-auto system, I need to talk about the muzzle device. Included with the upper is a PWS FSC556 flash hider / break combo thingee. It's very unique looking and gets great reports from around the interwebz...FN even uses it on their SCAR rifle. Regardless, I'm now doubly married to the SilencerCo SpecWar setup with one can in the safe and one can in jail. Because of this, the second thing I did after unboxing the upper and removing the picatinny adapters was to replace the FSC with a SpecWar Trifecta Brake. I will be selling a new, FSC takeoff on this very site in the near, near future.

Pics of the muzzle device - did I get the model number right I wonder?

For the first range trip, I installed the SiCo blast shield over the muzzle brake because I'm a considerate guy and didn't want to drive away other patrons at the range.

Ok...the gas system. AR piston systems are a very polarizing topic on just about every forum you visit. I'm not going to rehash those pro/cons but instead I'll talk to what drove me towards the PWS. I've owned Adam Arms uppers previously but they didn't really do anything for me. The short-stroke piston system felt flimsy and dumped tremendous amounts of hot gas right underneath my Magpul hand guards. At one point, I thought that I was about to melt them with an AA Midlength 14.5" setup at only around 160 rounds down the pipe. Also, the AA system didn't seem to keep the upper receiver any cooler or the bolt carrier group any cleaner. What the hell, right? Even though both units I owned performed flawlessly (my other setup was a 7.5" AA), they really didn't seem to offer anything over DI to make them worth the complexity, weight, and cost.

Enter the PWS. Primary Weapon Systems has made their name on a very unique long stroke piston design. The easiest way to describe it is that it's a hybrid version of an AR and an AK. The BCG (bolt carrier group) is non-standard in that the gas key is replaced with a rod that runs the full length to the gas port where it mates with a specialized gas block. It looks very similar to an AK gas rod and the mechanism works about the same way - or so I'm led to believe.

So why? Well for one, I'm lazy and hate cleaning. Direct Inpingement ARs have served me well but they are an absolute bitch to clean. I have spent many, many hours scrubbing the dirty DI BCGs with harsh chemicals and a toothbrush. They are icky and anything that prevents me from having to go through that routine is - or may be potentially - worth it.

Also, as I alluded to before - I'm now in the suppressor game. Sound suppressors - or cans - have played hell on my DI rifles. For one, the dirtiness I described before is magnified times three when shooting a DI gun with a can. Also, the gas blow-back from the upper receiver port and around the charging handle can bring tears to your eyes - literally. So, in buying the PWS upper - I'm looking for a cleaner, less-gassy rifle that will better function with a sound suppressor.

Back to some mechanics...

Because of the unique setup of the PWS piston, cleverness was needed to interface a standard AR charging handle with a full length piston. To do this, the thoughtful inventer designed the piston in a two piece design that can separate easily half-way down the rod. The piston can be separated into two parts when the upper portion/upper rod is rotated and aligned to a certain angle. The charging handle can then be removed or inserted. FYI...the upper comes standard with a BCM mid-size charging handle. Big plus for this because I update every one of my AR rifles with the exact same model as soon as I can.

Pics of the setup:

Note that these were taken after the first range trip. I fired exactly 180 rounds so there is some carbon. The BCG and piston arrived very clean and very well lubricated.

One minor note to mention, the assembled BCG, piston, and charging handle require a bit more manipulation to reinsert into the upper. It's not as simple as a DI gun but it not very difficult either. It just takes a bit more thought.

The gas block is pretty unique as well. It has five positions that can be adjusted via an included tool or with any pointy instrument.

The five positions are:
1 dot - normal operation
2 dots - high-powered military rounds unsuppressed
3 dots - normal suppressed operation
4 dots - high-powered military rounds suppressed
X - disassemble

One gripe, moving from dot one to two requires that the block assembly be turned counter-clockwise when looking down the barrel. If you turn the opposite way and move to the disassemble setting, the mechanism will eject from the block as it's under spring tension. I accidentally did this when I first inboxed it and I had to remove the rail to reassemble. Not a huge deal, but I wish it were more intuitive or required more effort to move to that position.

More to follow..

Expect part 2 - first looks and range outing coming soon.

 

[Cudruln]

Good write up. Ready for round 2

 

[boss_hawg]

Part 2: First Range Report

So I slapped this upper onto my RRA lower and took it up to my local range this afternoon. For the first visit, I had intended to fire off 200 rounds - 100 Independence XM193 FMJs (5.56) and 100 Freedom Munitions 55 grain 223 reman's.

I used Brownells 20 round mags for the Independence and 3 Brownells 30 round mags for the FM ammo. The remaining 10 rounds went into a Magpul 20 round mag.

Within one mag of the Independence ammo, I was sighted in at 35 yards. I then proceeded to fire off most of the remaining Independence ammo getting decent groups from a rest. I shot 80 rounds of the Independence ammo in total.

I am not a highly skilled marksman, but I was able to achieve sub 1" 3 and 5 shot groups at this distance. I have no doubt that this is a sub 2 MOA rifle given quality ammo and a quality shooter. Neither were on hand for the first trip - I only intended to check reliability, carbon accumulation, and sight in the optic.

All rounds fired reliably with the only issue being that I did not fully insert one mag before releasing the bolt. The resulting bolt-hanging- over loaded mag was quickly and easily remedied, and that flaw is attributed to operator-error vs. a flaw in the equipment.

After I was sighted in and the rifle was nice and toasty, I then turned to the Freedom Munitions rounds. For the most part, reliability was excellent until I encountered one issue.

The rifle jammed on a failure to extract and feed the next round of FM reman's, and I was stuck momentarily wondering if I up had just shelled out a good bit of cash for a dud. Pulling the charging handle did not remedy the situation. I dropped the mag and began to inspect further.

As you can see, it appears that I had some form of case separation. This was a first for me after shooting thousands of rounds through DI ARs, my Tavor, a Steyr AUG, a Golani, a Sig 556, and an Arsenal 106 (chambered in 556).

Upon closer inspection, I realized that I have read of this occurrence happening with over-reloaded brass - particularly with Freedom Munitions. Also, I can see no reason why this particular setup would induce this type of flaw versus any of the others. At this time, I am chalking this one up to the ammo and not the weapon itself. I will keep shooting these reloads and see if I can replicate this error in either this setup or through another weapon system that I own.

One last point that seems worthy of mention: after 120 rounds, the hand guard had become quite warm. The receiver itself was still very cool but I had to equip a glove to fire off the remaining rounds. The heat was not excessive compared to some of my other setups but the long-stroke piston is not the "end all" for alleviating heat.

Upon returning to my basement, I did find that the BCG was much cleaner than I have experienced firing 180 rounds through a DI AR. Much of the factory lubricant is still present and the NIB coating (or similar) on the PWS carry easily wiped clean...big check in that box.

I will attach some pictures below, but that is it for the first outing. Expect more in the future...I want to see how this setup reacts after a couple of thousand of rounds - especially suppressed.

My initial reaction is positive and I'm thinking that this may become my "go-to" AR.

Questions, concerns, inquiries...all are welcome.

Sorry for the crappy pictures...my everyday cell phone is junk and the SSGC lighting is not good.

This was standing, fairly rapid fire. the target is roughly 6"x12" at 35 yards.

Not sure if it shows but the SiCo blast shield got hot/dirty pretty quick.

 

[boss_hawg]

all of the remaining freedom munitions rounds fired without incident. the only reason that I didn't shoot the final 20 independence rounds was that the gun was hot and I needed to let it cool before heading out.

 

[EugenFJR]

In...

 

[Wallace]

Kind of neat. Would like your input of the recoil impulse on the PWS vs the AA and DI guns. Also, do you perceive that the cycle rate is reduced or increased from this longer piston system?

 

[Cudruln]

Good follow up for part 2

 

[boss_hawg]

The AA / short-stroke piston seemed to be more of a "push" vs. the "snap" of a DI rifle.

I did not focus as much on the PWS long-stroke impulse but it wasn't as different from a standard DI gun like the AA setup is. I think this is due to the fact that - like a DI gun - you only have one part moving even though that part is a combination piston / carrier group.

The short-stroke piston system I believe has two or three parts moving independently of each other.

 

[boss_hawg]

Kind of neat. Would like your input of the recoil impulse on the PWS vs the AA and DI guns. Also, do you perceive that the cycle rate is reduced or increased from this longer piston system?

As to cycle rates - like everything else - it's going to be highly variable based on a number of other factors as well as the piston system.

For one, I'm using a standard CAR buffer and spring with both 5.56 and .223 on the most "wide open" setting (at least for now). I'll make a note to vary maybe the buffer weight and the gas port setting to see if I can achieve a short-stroke or failure to eject.

Also, I have no objective way to measure this because I don't have access to a FA lower. I would hate to "perceive" something that can't be measured with my setup.

As a teaser, the next outing will be with a Specwar 762 attached. I expect to also post a review with a Specwar 556K sometime this summer once my stamp is in.

 

[boss_hawg]

Just to update you guys, I found another full 30 round mag in my bag when I checked it this evening. That would mean that I only fired 150 rounds on the first outing and not the 180 rounds that I previously stated.

I will be giving more updates this weekend as I put more rounds through this setup.

 

[Jake]

Very nice write up. Tagged for future updates...

 

[boss_hawg]

Very nice write up. Tagged for future updates...

Thanks!

You're in luck...the future is now.

Note that I type these updates on my iPad but then go to my phone to insert photos. If you catch me between edits, you'll see some tag/reminder that I leave for myself to add a photo at a later time. Well...let's get down to it!

Today I took the PWS upper out again to continue putting her through the paces. I left my house with 200 rounds of freedom munitions remanufactured 223 in 6 thirty round mags (5 Brownells GI, 1 Troy "Pink Lips" Black Mag / Pink Follower) and 1 twenty round GI mag. My purpose was to continue to test accuracy and reliability while noting any differences between this and a standard gas DI (direct impingement) upper. The added variable today was my SpecWar 762 suppressor.

As many of you know, sound suppressors can play havoc on their weapon hosts. The added back pressure can (pun intended) increase cycle rates, dump additional carbon into the action, and lead to added wear 'n' tear on the host's components. The gas piston upper is touted as a solution for some of these problems.

The setup today was the same as before: 35 yards with some of the shots being from a pseudo-rest (bag rest but I am standing). While this doesn't simulate true bench shooting, it's all I can do given my current location (my bench shooting setups are 250 miles away). I used the same lower today that I used before - standard RRA lower with a CMC single stage trigger (it's nice!). Optic is a Nikon M223 1.5-4.5x. I shot 4.5 magnification the whole time.

I sent the first 3 rounds down range without the sound suppressor to check my zero. My SpecWar causes significant but predictable point of impact shift on every 223/556 rifle that I've mounted it on (down and slightly left). Here was my first group.

I dialed the Nikon left and down a bit - and I felt good to go with the sound suppressor. I only meant to shoot three rounds or so but the joy of suppressed shooting was too much fun. I ended up shooting most of the 20 round mag.

I then covered up those rounds with target stickers and fired off another 30 round mag.

Here are the results:

This was my best group of the day...if I recall.

I then shot another mag with similar results.

At this point , a couple of things to note.

Accuracy - even at 35 yards - is what I would consider to be "good." I am not a skilled marksman, but I could tell when I was jerking the trigger. I saw holes where I expected to see holes in the target given the sight picture when the round went off.

Second, even though "gas in the face" was improved...it was noticeable. I would estimate that the gas is reduced by half, but I later did a mag dump and my eyes were watering about twenty rounds through. I consider this a "push" - better but not a 100% solution.

Also, the recoil is easily controllable by the selectable gas block. I dialed it all the way down to the lowest setting and reliability was 100%. The piston "push" became much more noticeable but the recoil wasn't even driving the scope's sight picture off of the target. To me, this is a big plus.

Then on the fourth mag, I ran into some issues. The first round fired but the next round did not completely chamber (though the bolt looked closed). I dropped the mag and extracted the round. The failed round had significant marks and dents on the casing...boo. I reinserted the mag and fired another round. Failure; this time more pronounced as a FTF as the round got less close to fully chambering.

I repeated this cycle three more times before giving up. I was frustrated but I wanted to find out the cause. There were five rounds fired and five dented rounds pulled from the chamber in varying degrees of failure. I dropped the mag out of the gun and tossed it back into my range bag.

I pulled a new mag out - the Troy "pink lips" lolz - and blazed through 30 flawless rounds...maybe it was the magazine? All of the remaining mags were fired without incident. I am trying to be as objective as possible, but I am going to attribute this failure to the magazine. I have never used this particular one - it's kryloned tan - with this lower. Perhaps something was "out of spec?"

Anyway, as i mentioned, all remaining mags were fine. I'm going to look into this particular one to see if something's amiss.

In total, I shot 155 successful rounds with five failures on the one mag. Accuracy was typical of the first visit with the added inconvenience of the present-but-predictable SpecWar 762 point of impact shift.

Some "post range" observations:
-mags can be - and typically are - the weak link in must weapon systems
-cans are awesome but dirty. I also hate the heat they produce. I would buy a can with less decibel-lowering performance if it stayed significantly cooler
-I had the gas block turned to its lowest setting (least gas) for the SpecWar but forgot to turn it back up when I took the suppressor off. The gun cycled fine but the recoil was very low. I think this - plus the SpecWar brake - would make for a wonderful competition setup.
-speaking of the SilencerCo SpecWar brake muzzle device...I wholeheartedly agree with what Larry Vickers stated in the past two weeks: brakes are for competition use only and have no real application outside of that use. the SpecWar brake creates a concussive blast that is teeth-rattling, migraine-inducing, ear-pro-penetrating...but damn it shoots flat.
-the SiCo blast shield makes the SiCo brake shoot like the SiCo flash hider
-the chamber is dirty...not like a DI gun after this many suppressed rounds but it's still dirty

This concludes range report #2. I will continue to update you guys as I put more rounds through this one in the future.

Questions are welcome as are any specifics that you wish me to test.

 

[boss_hawg]

here are pictures of the bcg and upper receiver after the 155 rounds yesterday (at least 100 of them suppressed)

 

[boss_hawg]

After a two week hiatus, I should be back on the range with this rifle on Saturday.

At this point, I will only update you guys on the round count and any noteable observations that are new unless anyone wants me to test a specific feature.