Got Fireball? PWS MK-107 AR Pistol Arrives For Testing

Image: Chris Dumm for TTAG

As many of you will no doubt recall, I’ve been very skeptical of ‘pistols’ based on military autoloading rifles. I’ve consigned several of them to the Deepest Depths Of Uselessness abyss and many of you have vigorously exercized your God-given right to disagree with me. Loudly. Primary Weapon Systems has just loaned us a very posh MK107 AR pistol for testing, and as I play with this $1900 specialty firearm, I can feel my curmudgeonly skepticism starting to erode. If I’m ever going to change my mind about MSR-based pistols, this Wylde-chambered piston gun will be what does it . . .

Image: Chris Dumm for TTAG

That’s no DI gas block: it’s an adjustable gas port, which drives the slender long-stroke piston at the heart of this PWS’ action.

Image: Chris Dumm for TTAG

And here’s the other end of that slender piston, directly connected to the PWS piston bolt. It’s incredibly clean right now, and I fully expect it to stay that way.

Completing this brief stem-to-stern tour of the MK-107, this shows PWS’s in-house locking castle nut (which isn’t actually a castle nut), the BCM Gunfighter charging handle and the rear half of the Magpul MBUS sight set.

This beauty showed up just a few days too late to join me shooting in the pouring rain last weekend. So it won’t spit any lead until next weekend because we’re driving the sprog to a gymnastics meet this weekend. Next weekend, MK107…next weekend.


  1. avatar Thomas says:

    Any word on a ccw holster? /sarcasm

    1. avatar Vhyrus says:

      omg drop leg scabbard ftw!

    2. avatar Nigil says:

      Single point sling on shoulder + long coat = concealable RIflepistol.
      I’d totally do it, if only for the lulz.

  2. avatar Kagans says:

    You should put an SB15 on that bad boy.

    1. avatar gtfoxy says:

      This, for those of you NOT in the know… Obviously TTAG contribuotors…

      In GCA and NFA terms, put this on any originaly manufactured “stripped” lower with a barrel length less than 16″, but with a permanent OAL of more than 26″, and a VFG can be added.

      It can be shouldered if the need ever arises and slightly more control is needed. The official BATFE ruling is it is NOT a stock, therefore NFA rules need not apply providing the origins of the lower are aforementioned origins stated on the 4473 or it is manufactured from a “Non-Firearm” piece that was first assembled with a barrel shorter than 16″.

      Add a longer barrel than 16″ and put a stock on it and you have a rifle. Then go back as desired. Just don’t have a “Stock” on it with a short barrel.

      1. avatar JasonM says:

        According to the NFA having a vertical foregrip on a “pistol” makes it an AOW, which requires NFA registration and a stamp.
        Angled foregrips are perfectly legal, however.

        1. avatar gtfoxy says:

          Incorrect Sir.

          It is not a SBR nor a AOW as defined by the NFA. Over 26″ permatent length with a barrel of any length is a Handgun. If you add a VFG it is a Firearm, as defined by the GCA, providing it does not have a stock. The SB-15, as ruled by the BATFE, is not a stock, it is a brace.

          A firearm derived from an originaly manufactured rifle with a barrel less than 16″ is a SBR or a OAL of less than 26″ is a AOW.

          In addition, how you use a specific item (read Brace), does not change its classification. Nor is there any law defining the proper use, as determined by the BATFE, only the intention of the device in question.

          If this item in the review in question does not meet the 26″ rule, them yes, adding a VFG would make it a AOW.

          That could be rectified possibly by the addition of an A2 buffer. Same goes for a permanently attached barrel device. Over 26, not a SBR (that would require a stock) nor and AOW (that would be less than 26″).

          Page 2, question 2.

          If the OAL is greater than 26, it is not an NFA item. The addition of the SB-15 does not change the calssification.

        2. avatar JasonM says:

          I never claimed the sig brace changed the classification of a pistol. But according to the ATF open letter I linked to in my original post, a pistol is a gun designed for one-handed firing, and putting a vertical foregrip on one implies a two handed firing grip, making it an AOW.

          Most AR pistols I’ve seen, including the three in my safe and the one mentioned here, are under 26″ OAL, so they are subject to the AOW restriction.

  3. avatar jwm says:

    other than as a range toy the only use I can come up with for one of these is a CQB weapon. How often do we engage in CQB?

    1. avatar Justin says:

      Unless you are active duty, how often do you engage in any combat?
      — In my state you cannot legally keep a loaded rifle in your vehicle, but you can keep a loaded pistol. I keep one securely underneath the back seat of my truck.

      You would be surprised at how accurate my 7.5″ noveske is at 100 yards.

      1. avatar RockOnHellChild says:

        You engage a BG at 100 yard, better have a damn good reason for the police why you did so… Real world civilian gun fights don’t happen like that.

        1. avatar TheBear says:


          Even in Iraq and Afghanistan, nobody I’ve ever personally known has engaged anyone past 100 yards.

          Modern warfare doesn’t happen in trenches squared off against each other 500 yards apart. At least right now, it’s a lot of kicking down doors, ambushes, and street fighting.

          And of course most civilian DGUs are within 10 or 20 feet.

        2. avatar RockOnHellChild says:

          Very good points, bear.

          I would also like to add that if you’re carrying a pistol, as you should be, given you live in a freer state, of course.

          If it’s robbery, no going to your truck, the truck isn’t your holster. If it’s an active shooter, pull your pistol and go to work, take care of business, maybe save some lives, don’t run to truck and grab your rifle.

        3. avatar PapaChop says:

          TheBear – wrong on that one. Many engagements in AFG have been at way over 100m – it’s one of the major reasons SMs have been complaining about the M4.

        4. avatar RockOnHellChild says:

          So, with complaints about the 14-20 inch barrel versions at that distance, what is the effectiveness of the 7 inch barrel version?

          May cause several welting…?

        5. avatar Jonathan -- Houston says:

          It just depends on the mission, so to speak. For civilian purposes, a self-defense use is not going to be justified at 100 meters. Beyond length of your house distance, you’d really have to be talking about major civil unrest, like rioting, before you could get away with that.

          In combat, that also depends. There were lots of CQB situations in Iraq, some in Afghanistan; but there were also open desert encounters in Iraq and mountainside battles in Afghanistan, both at long range.

        6. avatar RockOnHellChild says:

          Civil unrest, my happy ass is slinging a standard length rifle, which is legal here, but regardless, laws be damned at point.

          1. Survival
          2. Everything else

    2. avatar RockOnHellChild says:

      Home defense is all about CQ…

      But, the reality is if you’re so close that you should’ve brought this over a standard length, long gun, you will likely be using it as a bludgeoning tool to get the guy off you.

      Which is also why all my long guns have slings, so I can let go of them and use my hands without losing control of the weapon.

      These things, wholly useless as far as I’m concerned.

    3. avatar JasonM says:

      If you live in a state that prevents keeping a loaded “rifle” in your car, but permits keeping a loaded “pistol” in the car (like here in WA), they make great car guns. And being tiny is an advantage there as well.

      With a long buffer tube and a cane grip on the end, or the new Sig brace, it’s not much different than an SBR.

  4. avatar Rustholio says:

    Most practical use is hunting.

    A lot of places don’t allow hunting for deer except with a pistol or shotgun. This gives one the chance to use a rifle round in a pistol without wicked recoil.

    1. avatar Evan HB says:

      Yeah, but a lot of places specify a straight walled case in pistols for hunting. And with the extreme loss of muzzle velocity it would not be nearly adequate for hunting anymore(game with any real size past small varmints).

  5. avatar BR549 says:

    Looks like a well made piece, but in the end, what do you have? An exceptionally loud pistol that never gets a chance to fully utilize the charge or the projectile that come in the 223/5.56 format. Now, if someone happened to do reloads with a lesser amount of a faster burning powder, perhaps we might be off on the right foot, but by doing so, one would be eliminating one of the strongpoints of having a piece such as this and that would be interchangeability of magazines/ammo with fellow compatriots in the field.

    You NEVER EVER want to discharge this thing indoors or in a closed space when you don’t have hearing protection. If you do, you’ll destroy your hearing; period. One of these going off out in the open is bad enough to convince you to never forget your mouse ears or plugs again, but who is doing to want to fumble for hearing protection when noises are heard at 3:00 am?

    I have the KelTec PLR16 and have gotten the thing hot with no problems at all. For the money, it’s a far better buy and it doesn’t have (nor need) the rear protruding buffer tube. With a muzzle break, muzzle climb is barely noticeable. Still, in order to make this functionally useable in clearing a house, you’d have to customize your reloads, but then, as I said, you couldn’t trade mags with anyone having a traditional AR platform.

    Interesting toy.

    1. avatar gtfoxy says:

      Suppressors on pistols cartridged to run sub-sonic well.

      End of story.

  6. avatar Rabbi says:

    Put a Sig Pistol Brace on it and have a ball!

    I have a 11″ PWS upper in 6.8 SPC. Makes up for the reduced stopping power of the 5.56

    1. avatar Hobbez says:

      Exactly. 300 blackout, 10.5″ barrel, and a buffer tube milled to put Sigbrace out at stock length makes for a highly effective, ATF legal, home defense weapon. Truth is, if your using your pistol AR as a pistol, then your doing it wrong.

      1. avatar Hasdrubal says:

        My new house gun is a homebrew 300blk, 8.5″ barrel and a Troy Claymore muzzle device. Doesn’t strictly speaking reduce the volume, but the concussion felt when shooting indoors compared to a standard length .223 is significant.

    2. avatar Accur81 says:

      The 6.8 and 300 BLK are still good for over 1,000 FPE out of an 8″ barrel. A colossal fireball, to be sure, but still plenty of power for CQB and short range hunting.

      Let’s also not for get the LA Riots type of self defense scenario: Korean shopkeepers quietly standing on top of their shops with shotguns and rifles. I can help but imagine a big ‘ol AR pistol would have a similar effect.

  7. avatar JohnnyMac says:

    Why does a piston gun need a buffer tube?

    1. avatar Matt in FL says:

      The bolt still has to have somewhere to go.

      1. avatar RockOnHellChild says:

        And, a place for the spring, which sends the bolt forward…

        1. avatar Matt in FL says:

          Oh, I just figured you tilted it muzzle down and gave it a little shake, the same way you’d reload my old M16-style air rifle.

        2. avatar RockOnHellChild says:

          What do you call that, partial automatic?

      2. avatar gtfoxy says:

        Most captuered spring piston systems do not require a buffer, tube or stock/ brase of any kind. RRA, Spikes and others make these systems now. KAK made one years ago.

        They work good in pistol calibers for home defense: A primary topic of discussion on these commentaries.

        1. avatar Aaron says:

          The Extar Exp does not have a buffer tube and is far more cost effective than this at $450.

      3. avatar JohnnyMac says:

        I assumed something like that, but obviously the AK47 / Galil / SIG55x / Mini-14 / AR-180 piston guns do not suffer from this problem. I take it the answer I was looking for is along the lines of “the length of the receiver of the AR-15 is too short to accomodate the bolt and spring during recoil without additional extensive modifications”

        1. avatar Matt in FL says:

          Yeah, a standard AR bolt carrier group is only about 3/4″ shorter than the upper receiver that contains it. Just retracting it far enough to extract an empty casing causes it to protrude from the back of the upper (into the buffer tube) by about 3″.

        2. avatar Jeff says:

          it’s pretty amazing that this stupid design element of the AR platform wasn’t resolved decades ago.

        3. avatar DBM says:

          Why does that surprise you? The thin barrel has always been a problem. Overheats easily and warps making accurate fire at any range impossible. The Marines were developing the M-16A2 to resolve problems and one of them was barrel overheating. The original design was for a rifle with a thick barrel. The Army took over the program because they wanted to adopt the M855 round and the SAW. Because the army didn’t want to spend a few thousand to redesign the mounting hardware for the M-203 they reduced the barrel diameter to its original size from the front site post to the receiver. Thus they managed to ignore the Corps needs and greatly increase the cost of production at the same time. The 203 has long been known as a dude launching system especially when used in soft sandy areas and marshy ground. Not to mention its and indirect fire weapon making it hard to use in a lot of situations.

    2. avatar Azman says:

      Good question. Anybody who knows? I sucketh at ar-15s

      1. avatar Brandon says:

        Matt’s answer is correct.

        1. avatar 'liljoe says:

          my bolt goes to Kentucky

        2. avatar RockOnHellChild says:

          My bolt prefers warm weather, snowbird… temperamental ass AR, figures.

      2. avatar MarkP says:

        The reason a piston AR like a Barrett Rec7 and Sig 516 have buffer tubes is exactly what Matt from FLA said. There are however piston ARs such as the Rock River Arms PDS rifle which has a full length guide rod and recoil spring located above the bolt carrying group and barrel like an AK. This type of configuration allows for a folding stock or no stock at all. I have their PDS pistol which is pretty amazing mechanically speaking, and stays very clean and cool.

  8. avatar DBM says:

    What is the actual max effective range of both being able to hit the target and lethality?
    BR549 (HeeHaw) although I am definitely no expert on this I wouldn’t load a faster burning powder into the ammo. The increased chamber pressure would probably destroy the weapon and you. Even in 20 inch barrels there is unburned powder coming out of the barrel. I’ve wondered myself if so much of the powder is getting burned outside of the weapon why isn’t ammo and rifles being redesigned to have reduced powder loads (necessitating shorter brass) to operate more efficiently. The 7.62 x 51 is an example of that concept. Its just a shortened case 30-06. Lots of empty space inside of an 06.
    Can anyone out the with knowledge on this subject educate me on it?

    1. avatar Russ Bixby says:

      I’ve often wondered why no one makes a primer that extends almost to the base of the bullet and spews sideways at the tip.

      If the charge burns from front to rear, things are far more efficient. That’s why the pinfired shells worked so well.

      Ah, well…

      1. avatar DBM says:

        Early model M-2s issued to SeaBees in WW2 had extremely short barrels. I want to say about 28 inches. That resulted in massive amounts of powder being thrown out of the front of the gun and then a massive flash burn. The old SEaBee that old me about it said they gave him a small broom to push it down but he decided to get some kitchen matches from the mess tent and throw a lighted one over the sandbags to ignite it so he wouldn’t get blinded. The problem ended when the longer standard barrels were issued to them.

  9. avatar Matt in FL says:

    I like stuff that PWS makes. I would have one of these on my “because why not?” list.

  10. avatar Bill says:

    hint, you don’t shoot an AR pistol like a pistol, you ut your nose to the charging handle and shoulder that bich

  11. avatar Brandon says:

    I can see very specific real world reasons to have an AR pistol, but the blanket answer (and the one I would use) is because I can, ‘Merica.

    1. avatar B says:

      I’ve got an AK and an AR pistol (both with Sig and CAI braces.) Holy crap, shooting the M85 is like shouldering and firing a pogo stick. So much movement going on in that gun. Basically, these are solutions to the stupid contradictory gun laws like others are saying. Can’t have a loaded rifle in your car, can’t own an SBR, can’t hunt with a rifle.

  12. avatar Adam Bolton says:

    Think of it as an SBR without a tax stamp. You can take it home immediately after purchase and start enjoying. If you by a lower and get it registered then you can use it as originally purposed. The AR pistol is not meant to be used in a combat situation IT IS A LOOPHOLE. I have a PWS 107 pistol and I love it! I abandoned the pistol lower, but it now houses another SBR upper. Put a tennis ball on the buffer and go to town.

    1. avatar gtfoxy says:

      Please do not refer to liberties as “loopholes”.

      We do not want to further bolster the ignorance of the day.

  13. avatar Russ Bixby says:

    Now for a Kalashnikov version…

    Держи меня за бутылку водки и смотреть это!

    1. avatar scoutino says:

      Translation sux. It says “Grab me by my vodka bottle and look this.”
      Looks like the case where computer translated the saying “Out of sight, out of mind” to russian and than back to english as “Blind idiot”.

      1. avatar DBM says:

        My resident translator said your translation was correct but nothing she’s ever heard said in Russia. Kind of like Kine Shisa (really bad spelling) in German.

        1. avatar Russ Bixby says:

          Yeah, Russians usually are to smart to say “Hey y’all, hold my [drink] an’ watch this!”

          Near as I can figure, what I wrote is what I meant: “Hold for me bottle of vodka and watch this!”

          Y’know, Kalashnikov…?

  14. avatar defensor fortisimo says:

    In an unrelated note, can anyone else picture “got fireball? ” becoming a slogan on a LARP t-shirt?

  15. avatar Robert says:

    Love the WTF is that factor.

    1. avatar RockOnHellChild says:

      I wanna see someone CC or OC this…

      What’s the problem officer, it’s a pistol, is it not…?

      1. avatar gtfoxy says:

        In some states, such as WI this is perfectly legal to carry as a Handgun in your vehicles, even when equiped with a SB15 brace.

        1. avatar RockOnHellChild says:

          No vehicle, I’m talking about carrying the thing…

        2. avatar gtfoxy says:

          A Concealed handgun is a concealed handgun, as concealed is concealed.

          If it falls under GCA guidelines of a handgun because it was not originaly created as a rifle, it is a handgun, and is a handgun. Conceal away providing there are no STATE laws prohibiting its use. There are no federal laws to that extent.

  16. avatar Boris Waltham says:

    Thats a great price for a great piece.

    1. avatar Ralph says:

      Quoting Charlie Sheen?

  17. avatar Bonkers says:

    Without the magazine in it, it reminds me of a stormtrooper gun…

  18. avatar S.CROCK says:

    this thing has “never going to be legal in my state written all over it.” 🙁

  19. avatar David says:

    Are any of you guys reloading? I got some brass and bullets from
    Had 1k primers on hand. Having a bit of trouble finding powder though. Anyone using 4895?

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