The National Firearms Act of 1934 is possibly the most outdated body of firearms regulations in the United States. There, I said it. And I stand by it. The improved shooting experience of using a silencer notwithstanding, the rules and regulations surrounding short barreled rifles (SBRs) is downright criminal. I was never a fence-sitter on the issue, but having the PWS MK 107 AR Pistol in my grubby mitts for a few months has done more to convince me of the asininity of the regulations imposed on the citizens of this fine country than anything else has. Truth be told, I never really understood the appeal of SBRs until PWS put this gun in my hands. It’s a very effective tool and a downright blast to shoot and here’s why . . .
Before I get into the meat and potatoes, though, let me give you a peak behind the curtain for a minute. We’ve already covered how gun reviews work at the dead tree mags. TL;DR: Pay to play and don’t say anything bad. See Remington R51 coverage for further proof. Here at TTAG, and really any other “new media” outlet, we usually have to shamelessly beg and plead to get guns to test. And we can usually tell how a gun review is going to go based on how the media reps for a company communicate with us. If they impose a series of restrictions about ammo selection, conditions of use, etc., the gun is likely going to have some issues.
That’s not Primary Weapons Systems. First, they hand over the goods with no conditions. I’m paraphrasing, but the message is fairly clear. “Shoot whatever ammo you want, as much as you want. Beat it up. Our guns run all the time, every time.” PWS does a great deal of testing internally including multi thousand round strings of fire with no cleaning or maintenance, and machine gun runs to keep things lively. Suffice it to say, nothing I’m going to do is going to be more strenuous than what they do internally. A point of view I challenged to the best of my abilities during this test.
Then, they have the patience of Job. If you go back through the archives, we first received this gun in February 2014. Chris Dumm was originally slated to test it, but his day job has kept him extraordinarily busy. He was only able to get to the range a few times before his world got so busy that finding keyboard time was nearly impossible. So he sent it my way the week before my wife and I bought our first house, an event which destroyed my free time and ammo budget. So getting a review of this gun has taken two authors and the better part of five months. To to PWS, we extend our apologies. This has taken too long and we’re sorry.
When Chris mailed the MK107 off to me, he sent me the following note.
Direct-impingement AR pistols are usually really picky with ammo; the gas systems are usually overpressured because they have to harness the same amount of gas in a much shorter amount of time. As a result their timing is very critical (and frequently off) and they beat the crap out of themselves.
The PWS is a totally different animal with its piston system. It was totally reliable with 200 rounds of mixed milsurp, Remington Green Box, and steel Tulammo. I couldn’t do accuracy testing because my local range doesn’t allow ANY AR-based pistols or AK-based pistols either. Too many morons have put rounds over the top of the berm with them at 100 yards, I think.
The velocity loss is also pretty bad with a super-short barrel. I didn’t get to chrono it, but 7.5″ ARs get 2100-2300 fps instead of the 3000-3100 you’ll get from a 16″-18″ barrel. Small bullets need high velocity to perform well, and when the little 5.56 bullet sacrifices 25% of its velocity for a short barrel length, it also loses nearly half its energy.
From really short barrels, the 5.56 stops acting like a rifle cartridge and starts to behave more like a 5.7.
Even with the SIG brace, an AR pistol isn’t exactly the most comfortable instrument ever devised. It’s WAY better than propping the buffer tube against your face, but it’s no Magpul CTR.
This is the only AR pistol I would ever own, but it still just doesn’t speak to me. It is a lot of fun, though, and I hope you have a ball with it!
The PWS MK107 Pistol is an AR 15 platform pistol platform sporting a 7.5 inch 1:8 twist barrel chambered in .223 Wylde. This particular gun features the SIG Brace, otherwise known as the poor man’s SBR kit. Using the brace as intended means strapping it to your forearm for additional support. The unintended usage (wink, wink) is to slot the brace in your shoulder pocket and use it like a rifle stock. Not that anyone would ever do such a thing.
This pistol also features PWS’s proprietary piston design with 4-position gas system. Said system includes settings for suppressed and unsuppressed firing with standard and “hot” loads. It also features a fifth setting to be used for annual maintenance of the gas system.
Story time re: that gas system. This gun arrived at my FFL very well used. The barrel was dirty, but the insides were clean. Chris seemed to take PWS at their word when it came to ammo selection and I know his note said “mixed,” but I’m pretty sure he used a few rounds of Remington Greenbox, and the rest was TulAmmo. This gun appeared to have been eating dirty steel-cased Russian 5.56 for breakfast, lunch, and dinner.
I didn’t clean it when it arrived either, so my first range trip took a disastrous turn when I tried to adjust the gas system to see how the various positions affected performance. I maintained at the time that carbon buildup around the gas system prevented me from switching it from the “X” position (used to disassemble the system) to any of the four production systems. I can also be an impatient idiot. In a spectacular combination of “What’s the worst that could happen?” and “Hold my beer and watch this!” I decided to let off a round with the valve turned to the X position.
To this day, I’m unsure of my logic, but the end result was watching a spray of parts fly out the front of the gun followed by a great deal of four letter expletives from the operator behind the gun. Remember the patience of Job thing I mentioned earlier? Well imagine my surprise when PWS’s response to me field stripping the gas system of their fancy gun with force was to send me replacement parts and ask if I needed another copy of the manual. No further questions asked.
I took the opportunity when reassembling the gas system to really clean the area around the gas system as it had a pretty good amount of built up carbon. I had originally assumed that carbon build-up prevented me from turning the valve from X to any of the four production settings. Once cleaned up, I still found the valve to be very hard to turn from the X setting. It requires a cleaning rod or other sturdy implement and a little bit of leverage to accomplish. It isn’t exactly tool-less in my experience, but I feel that most people don’t suddenly find themselves going from standard pressure loads to hot loads with a silencer. Your mileage might vary.
Destructive attempts completed, I found the gun (with all the parts back in place) to be dead-nuts reliable. I ran PMC bronze, XM 193, a bag of random 5.56 I found, Liberty, as well as some Black Hills 60 gr. V-Max. I’m not exactly sure how many rounds Chris put through it (it was a lot, based on the accumulated gunk), but I ran a few hundred with no failures. The gas system is so consistent that standing in one place and shooting makes for a neat little pile of brass for later pickup.
Since an adjustable piston system is basically witchcraft to me, I was also curious to see if changing the gas system setting would affect muzzle velocity. That’s probably a silly question, but I had ammo, a chrony, and a gun so double checking wasn’t hard. And no, gas system position doesn’t affect muzzle velocity. I did however find that position 4, the most restricted setting used for hot loads with a silencer, does mean short-stroking that leads to failures to chamber a new round. Open it up to position 1 (wide open), and those problems disappear.
Aesthetically, the PWS pistol is one of the better looking AR pistols out there. The machining work is flawless to my eyes, and everything fits together very well. With the exception of some commonly available items, PWS manufactures all of their parts in house. The only third party gear I could find was the SIG Brace, a BCM Gunfighter charging handle, and Magpul grip & BUIS.
Their barrels arrive at the shop as rifled blanks, which are then cut, chambered, contoured, and threaded in house. This level of control over the manufacturing process allows PWS to maintain a very high level of quality. The handguard is a free floated, keymod affair that attaches via 6 screws to the barrel nut. The top is all Picatinny rail and Picatinny, QD, and bipod keymod mounts are available from PWS. This particular pistol shipped with a tactical tan SIG Brace and Magpul BUIS. The whole package weighs in around six pounds on the dot, 6.004 lbs to be exact.
The gun feels very well thought out and balances extraordinarily well with the center of gravity slightly rearward of the mag well. I found the SIG Brace to be much more useful than a traditional padded buffer tube that you see on today’s AR pistol. Strapping it on made me feel a bit like a futuristic gun-wielding robot. A RoboCop costume is approved for purchase, so be on the lookout for a video making my dreams a reality.
The only way to get a two-handed grip while using the brace as intended is to extend both hands fully which makes using Magpul’s BUIS impossible. And while it’s only six pounds, that’s still a lot of weight to hang out there at arm’s length. Using the brace as a stock, though, the gun is a VERY maneuverable, and extremely lightweight pseudo rifle. It’s amazing what chopping a few pounds (and 9 inches) of barrel, gas system, and handguard off a heavy-barreled carbine-length AR 15 can net you.
There’s still something to be said for a true SBR — namely adult-sized length of pull — but if you live in a state that disallows SBRs or you’re in ATF purgatory waiting on paperwork, this is an EXCELLENT option to hold you over. I’m a hair under six feet tall and normally wear 42 regular suit jackets. I found the whole package to be ever-so-slightly cramped shooting it like a rifle, but that’s to be expected with such a compact package.
A word to the wise: don’t shoot this gun indoors without a silencer or doubled up hearing protection. Running ammo meant to burn in 20 inches of barrel in a system that’s only 7.5 inches long means that there’s a great deal of muzzle blast. The Triad muzzle device does a great job of killing muzzle flash, but holy moly is it loud. It isn’t bad if you’re the one running the gun, but spectating is a downright religious experience. You feel the blast more than you hear it. If you end up owning one, I’d relegate it to outdoor usage only.
The PWS muzzle brake/flash hider combo does an admirable job of managing muzzle rise and flash but boy howdy is it noisy. Did I repeat myself? Must have lost my hearing or something. Recoil is laughable for all but the daintiest shooters. And by that, I mean toddlers. The light weight means a great deal of control over the whole package. I had no problem double and triple tapping my way through PMag after PMag of 5.56.
The trigger is definitely good, and in the world of stock triggers, probably the best one out there. Viewed through the lens of “all triggers available” it doesn’t beat my Timney or any of the other high end manufacturers. However, it’s miles better than a lot of the trashy milspec triggers shipping with ARs today. It’s a single stage affair with NO takeup, just the very tiniest bit of creep and a glassy break. Really, the only fault I can find is that it has a heavy (my opinion) pull. It measured out right around 6.25 lbs. I’m a fan of 3 pound triggers, but if you prefer a sixish pounder, this is going to be perfect for you. All of the other controls work great including the very nice BCM Gunfighter charging handle.
I mounted a Primary Arms Aimpoint Micro knockoff for use at arms length as well as in the far more comfortable rifle posture. This setup worked better than the irons that ship with the gun. Future owners might also consider a larger unmagnified optic with a flip over magnifier.
I found the gun to be acceptably accurate with a realistic eye towards effective range. For my accuracy testing, I shot the MK 107 at a precisely measured 50 yards using an 8X scope with the front and rear of the gun supported with sandbags. The PWS appears to really love XM 855 as I was able to put up fairly consistent 1 (ish) MOA groups.
I spent a Friday afternoon shooting five different types of ammo through the MK107, a yet to be reviewed PWS DI Upper with a 14.5″ barrel, and my old steady Armalite with a 20″ upper. I found that the MK107 was putting up muzzle velocity numbers from 2367 fps for AE 223 to 2754 fps for PMC Bronze. If I were to use the MK 107 for longer engagements, I’d definitely choose the XM 855 which showed promising accuracy and very consistent velocity shot to shot. It was exiting the barrel at 2713 fps with a standard deviation of 23 fps. Compare that to the same load out of my 20″ barrel (3343 fps). What that means in practical terms is that at my elevation (~1600 ft) on a 90 degree day, muzzle velocity out of the MK107 is equal to the same velocity, and thus energy, at 200 yards from a 20-inch barrel. What it also means is that it gets pushed around by the wind a bit more.
Gabe Suarez claims that 300 meter hits on man-sized targets are well within the realm of possibility with an AR 15 pistol, but I didn’t take the opportunity to stretch the legs of this diminutive package quite that far. This is a sub-200 meter gun designed with maneuverability in mind. Making it do something other than that is asking it to do something it isn’t designed to do.
After zero cleaning of any type and at least 500 rounds of various ammo, the receiver is still just as shiny and new as the day PWS assembled it. In that time, I witnessed absolutely zero failures to fire, eject, load, or anything else save for the failures I caused by messing with the gas system (operator error)
Overall, I’m very satisfied with the PWS pistol in the role it was designed for. Slap a suppressor on it and you have a very maneuverable home defense gun that anybody in the family can operate effectively. Put in some earplugs, take it outdoors, and you have an awesome range gun capable of putting rounds on target out to 100 yards or more depending on your skill level. If your local club’s rules allow, this would make for a great carbine match gun as well. Or, if you’re jonesing for a SBR, but don’t want to negotiate the regulatory thicket, you can get about 90% of the way there with a MK107. If you’re waiting on paperwork to come back on your SBR, you can happily goof off with this until your federal permission slip comes back.
Specifications: PWS MK107 Pistol
- Advertised Weight: 5 lbs, 4 oz
- Actual Weight: 6 lbs
- Overall Length: 23.75”
- Barrel Length: 7.75”
- Advertised Muzzle Velocity: 2368 ft/sec
- Actual Muzzle Velocity
- XM 855 – 2713 fps
- XM 193 – 2376 fps
- PMC Bronze – 2754 fps
- AE 223 – 2367 fps
- Liberty – 2425 fps
- Chamber: .223 Wylde
- Barrel Twist: 1:8
- Price (retail): $1949.95
Ratings (out of five stars):
Fit and Finish * * * * *
This gun is a real gem. And for nearly $2000, it better be. The machining work is flawless and the coatings used seem to be very durable. The keymod system means a smaller diameter handguard which is a godsend for those with elfishly small hands like your humble scribe. It also allows a nearly endless amount of options for positioning lights, lasers, knives, blenders, and whatever else needs hanging off the handguard. The built-in buffer tube QD mount is perfect for single point sling usage and the included SIG Brace is well built and easy to use.
Reliability * * * * *
A piston system means your BCG and receiver stay cleaner longer which translates to more time spent shooting and less time vigorously scrubbing. Oh, and less dirt in the action to gum up the works. I had zero failures of any kind during my testing…except for those caused by me. On that note, my destruction of the gas system speaks to the reliability and robust construction of the whole rig.
Accuracy * * * *
I didn’t expect this gun to be a tack-driving mosquito killer. The effective range of the 5.56 round leaving a 7.5 inch barrel relegates it to a <200 meter gun in my opinion. Even 3 MOA, well within the realm of possibility at the max effective range of 200 meters, is a grouping that covers a man’s torso. To expect more than that seems foolish, no? That said, the PWS pistol was quite accurate with XM 855, a testament to great quality control, and solid manufacturing processes.
Ergonomics * * * *
Shooting the pistol as a pistol using the SIG Brace is an awkward affair and not ideal for long-term use and enjoyment. That’s a lot of weight to suspend at arm’s length and unless your upper body is built like Hafþór Júlíus Björnsson, you’ll tire quickly. Used in tandem with a properly adjusted single point sling, it’s a fairly usable system. Tuck that brace back in your shoulder, though, and you have a very effective, albeit cramped quasi SBR experience. Nine months of patient waiting and a $200 stamp will net you a longer length of pull…and that’s about it. Tuck everything in tight, grease up your Costa-like operator beard, and get to shooting this gun in the meantime.
Overall * * * *
While this would arguably be a more effective gun in .300 BLK, something PWS offers, this is still an outstanding firearm. It withstood my dumbass mishandling and kept on trucking. It was accurate enough, lightweight, and a real blast to shoot. I’m really grasping for nits that need picking to say that I’d prefer a lighter trigger. It’s one of the best stock triggers I’ve used, but it still isn’t perfect. If you set some realistic expectations about what your intended use case is, this might be a valuable addition to your safe. It is lightweight, portable, and doesn’t require a blessing from the BATFE to own. If you’re in the market for a SBR, consider giving PWS a strong look.