FAB Defense KPOS Glock Enclosure Review

If the three pistol to carbine conversion enclosures were cars, the FAB Defense KPOS Gen 2 would be a Ferrari: light, sexy, expensive, and requires a lot of maintenance.

The KPOS is my favorite enclosure for every day carry. It is the smallest and lightest of all the enclosures we tested, but also had several failures, including one that was not fixable without an external tool.

If you want the most compact SBR enclosure for your NFA registered Glock, the KPOS is your best choice.



The retail price of the KPOS G2 is $682 before shipping directly from the Mako Group, who imports the KPOS for Fab Defense.

I bought mine on sale, with a total price of just below $500 including shipping.

At retail price, the KPOS is the most expensive enclosure we tested, even accounting for all the extra pieces one needs to buy to make the Hera Triarii a functional SBR.


The KPOS body is aluminum. The folding foregrip / trigger guard is made out of plastic.I am not sure what the charging handle is made out of, but it is metal.

The KPOS has four rails. The bottom rail is mostly used up by the foregrip; I had just enough room to put a sling attachment. The top rail runs the length of the enclosure and is plenty long for an optic plus back up iron sights.

The stock of the KPOS is built in and folds to the right hand side. I am not sure why FAB Defense chose a right hand folder over a left hand folder, but this makes the KPOS very difficult to shoot properly without deploying the stock. The Triarii and RONI can be fired from a folded / compressed position if necessary.


There is a rubber buttpad on the KPOS, which does an okay job of absorbing some recoil. I was surprised at how “snappy” the KPOS and RONI felt when shooting my 9mm Glock 19.

The plastic foregrip has a few great design features, but I experienced difficulties getting mine to fold reliably. I really like that the bottom of the foregrip extends to cover the trigger. The KPOS is the only enclosure I trust to run with a round in the chamber. The foregrip is comfortable in my hands and it deploys easily.

The foregrip's bottom extends to cover the trigger guard

The foregrip’s bottom extends to cover the trigger guard


You push a button on the side of the foregrip to fold it, and this button does not always press down enough to unlock the foregrip.


I’m putting all of my weight on this button and it won’t budge. Gotta wiggle it.


I have learned to wiggle the foregrip slightly back and forth until the button depresses fully. Your mileage may vary, but I encountered this on both of my KPOS enclosures.

I also find the rear sling swivel to be troublesome. The KPOS ships with a single-point bungee style sling which I never used. Slings attach to the rear of the KPOS via a metal ring similar to a very small key ring. Granted, the KPOS isn’t very heavy, but I am concerned that this ring may fail during training or heavy use. I currently connect the KPOS to my body via a MagPul MS3 sling, and the MS3’s monster attachment jaws will fit in the KPOS’s small sling ring.


Putting your Glock pistol into the KPOS is a little complicated until you get used to it.

You have to:

  • unfold the stock
  • push down on the stock’s spring plate
  • slide out a captive pin
  • slide the retaining plate up
  • unhinge the front of the enclosure by pulling down sharply
  • release the locking bar by lifting the “tap” up
  • rotate the locking bar so that the “tab” is pointing down
  • slide the Glock inside
  • rotate the locking bar so that the tab is pointing towards you
  • lock the bar by pushing the tab down
  • snap the front of the enclosure back into place
  • slide the retaining plate over the rear of the pistol
  • push the spring plate down slightly
  • slide the retaining pin back into place

None of the steps are particularly hard, but it’s a LOT of steps. It’s comically more complicated than the Hera Triarii.

Even after talking with the creator of the KPOS at the 2014 SHOT Show I think the KPOS has two fundamental design flaws: the locking mechanism that mates the pistol to the SBR enclosure and the partial obstruction of the ejection port.

The locking mechanism is a metal bar that rotates into the small notch in bottom of the Glock’s rail. The rail itself fits loosely in the enclosure and the pistol rattles around inside pretty freely.


The locking bar rotates in either direction and then folds flat against the enclosure. If you rotate the locking bar so that the tab folds towards the barrel it is too tight on my Glock and has deformed the frame’s plastic. This also prevents me from working the charging handle.

If I rotate the locking bar so that the tab folds towards me it feels too loose. I can’t win either way.


I feel like the KPOS embodies what a pistol to carbine conversion should be. It’s as small as possible, very lightweight, and the additional points of contact allow for very effective shooting at higher speeds. It’s so easy to put a four round burst on a half-man-sized target at 15 yards it’s boring.

Unfortunately, reliability is the KPOS’s Achilles Heel. I have owned the KPOS for a long time compared to the Triarii and the RONI, and I have yet to complete a training or shooting session without the KPOS experiencing a failure of some kind. In firing over 200 rounds for this test, the KPOS failed five times, including one that required the use of a tool to fix the malfunction.

I believe there are three reasons for this, and the designer of the KPOS gave me a fourth reason. Here they are:

  1. The Glock 19 is too short for the enclosure, and the ejection port is partially obscured by the enclosure. Despite being assured this wouldn’t effect the reliability of the enclosure and that spent brass would be ejected well clear of the enclosure, my video footage shows that sometimes the brass bounces around and winds up inside the KPOS or worse yet back inside the chamber or even worse-worse yet BACKWARDS inside the enclosure and then hung up on the extractor.

    enclosure introduction-0

    Click to embiggen

  2. The deflector on the KPOS, in my personal unit, wound up bouncing brass into the chamber. I removed the deflector on my KPOS and in my case increased reliability. It did not make my enclosure 100% reliable.
  3. I don’t think the attachment mechanism between the KPOS and the Glock’s polymer frame is strong enough and/or has enough contact with the frame to allow for reliable function. There is a LOT of play in my enclosure. The Hera Triarii has a much more positive and secure locking mechanism.
  4. The designer of the KPOS told me that Gen 4 models (my G19 is a Gen 4) has enough differences from the Gen 3 to render the KPOS less reliable. He attributed this to the captive recoil spring and “general Gen 4 reliability.” My Gen 4 has the latest recoil spring from Glock, and both it and my second Gen 4 G19 function exceptionally well as pure pistols. Supposedly a new rear spring plate for the KPOS will help with this, but it’s been almost four months since the Mako Group promised me a plate and I’ve yet to receive it. I’ve contacted the Mako Group several times since SHOT Show 2014 and they were unable / unwilling to tell me if this new spring plate is available in new production models.

When the KPOS works, however, it’s fantastic. I am more accurate and my splits are faster when using the KPOS, and its small size makes it portable in almost any environment and situation. Mine currently resides in a hydration pack along with two 33-round magazines and a 15-rounder in the pistol.

I also dislike the charging handle. It looks like an AR-style handle, but it is hard to use by working just the left hand side of the handle. You’ll have a much easier time if you fork your fingers over the charging handle.

The handle is also in a spot that has the least biomechanical advantage compared to the RONI and the Triarii. The RONI had the most comfortable / ergonomic charging handle location, and the Triarii was considered the easiest by all those who handled the enclosure.

The KPOS stock is very short, and as such has the shortest length of pull amongst all the tested enclosures. In my wife’s case this is a positive, but in the case of some of my barrel-chested mutant Viking friends the KPOS was too short. There is no adjustability for the stock, making it the least friendly for people with longer arms, bigger bodies, and/or those wearing body armor.


As I said on my review from my other blog, I really wish I could recommend the KPOS. Besides the problems with the enclosure itself, the Mako Group has terrible customer service. Even after contacting me after my first review and conducting a special session at SHOT Show, Mako has been unable to fulfill their promises to make good with my unit and provide information on how other KPOS owners can improve the reliability of their enclosures.

I recommend the KPOS for people who have a Gen 3 Glock 17. I think the extra length of the pistol may make enough of a difference with the ejection port, and the KPOS was designed to be used with the Gen 3 models.

If you’re lucky enough to have an SBR Gen 3 G17 and need the smallest, most lightweight package then the KPOS is my favorite enclosure.

About the Author:

Short Barrel Shepherd Short Barrel Shepherd is a regular guy and works to make Web sites and mobile apps easier for people to use. He spends his free time attending fight-focused firearm, knife, and combatives training, motorcycling, writing, and playing games. His daily carry is a Glock 19 pistol and an AR15 .300 Blackout pistol in a backpack.
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24 Comments on "FAB Defense KPOS Glock Enclosure Review"

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  1. David says:

    My G17 / KPOS G2 should be coming out of NFA hell within the next month; I’ll let you know how it goes reliability-wise with mine.

    I definitely agree that Mako and FAB have not been completely forthcoming about some of the limitations of the G2 – for one thing, it apparently has some trouble running suppressed because you can’t lock down the suppressor to the bottom of the threads (the charging handle blocks it).

    I have _heard_ a rumor that there is a tactical-style charging handle for this thing that you might be able to acquire from Mako or FAB. Ask them nicely, I guess. I could be wrong.

    I am surprised you didn’t talk about the optics situation. Clearly, something like an RMR or Aimpoint Micro is the way to go (or a clone – I love those PA Micros!). But I don’t know what irons you could use on one of these…

    • Short Barrel Shepherd Short Barrel Shepherd says:

      What Gen is your G17? Either way I bet your situation will be better than mine.

      In regards to optics I have run the Primary Arms MD07 pictured as well as their now discontinued holographic sight that’s a Fast Fire clone.

      We used to run flip up BUIS similar to ones found on an AR15. After doing training with the KPOS last year I determined that shooting through the tube was accurate enough at 40 yards.

      • over-educated economist says:

        G17 Gen3. I admire your taste with the G19 Gen4 – I was thinking of getting one and pimping it out with an RMR.

  2. Mark says:

    “barrel-chested mutant Viking” I resemble that remark! Great review. Keep up the great reviews.

  3. Campersteve says:

    Appreciate the reviews. I can’t seem to locate the Glock SBR Hera review. That’s the one I’m most interested in. Thanks and keep up the good work.

  4. Dustin says:

    To increase it’s reliability what we do here in the Philippines is we cut 1-2 coils (spring) in the back plate and it works great even in full auto! BTW mine’s Gen 1 KPOS-it’s the one with the charging handle in the back plate. If you’re running it full auto we can buy here an autokit with a charging handle in it specifically made for enclosures like the KPOS and Roni. Also, if an autokit is placed the back plate needs to have a channel cut through in it in order for the autokit tang not to hit it. Lastly, it’ll be great if you can do a review on the Hera Arms PDW (GCC Stock System)-it’s the lightest and the most reliable in full auto of the Glock enclosures. BTW great blog on SBRs.

    • Short Barrel Shepherd Short Barrel Shepherd says:

      Greetings from the United States!

      That’s an excellent idea. FAB promised me almost 9 months ago to send me an “improved” back plate, and they never did. I wonder if it’s just one with fewer coils 🙂 I will try your suggestion. Thanks for your compliment, and I hope you keep reading.

  5. Jay Hardy says:

    Great write-ups on all three enclosures. I have purchased the Roni and a Gen 1 KPOS. Have you tried the Gen 1 KPOS with a much larger port for ejection since the rail is not continous? It seems that would make a difference in the reliability. At least I hope it does. They can be purchased used for about $300 so it helps keep the cost down. If it sounds like I haven’t shot them yet, you are correct. They are being stored with an FBI friend while I await my NFA stamp for the Gen 3 Glock 19. Hopefully will have it soon. Great blog!

  6. Jeremiah says:

    Thanks for another great review.I live in Europe and I’ve had my KPOS G2 for about 5 weeks now. Inside is a relatively new Glock 34 Gen 4 and it is running almost flawless. I use it for Low Velocity Rifle matches (IPSC) and had about 2 issues in over 700 rounds,mainly as you said the empty casing hit the KPOS ejection port a couple of times. On the other hand accuracy is great and even with a rather cheap UTG red dot installed it is childs play to get 4 rounds on target in the Alpha zone at an amazing speed.
    As you mentioned in your review it is absolutely awesome when it works and in my case it works just fine … I only had a about 2 stages on a total of 4 three stage matches where things went wrong due to hard primers on S&B 115 grain ammo. Just swithced to another box and ran fine again…So purely a bad box of ammo. I do not have the wobble on the gun like you have but maybe that is because of the size difference between the G19 and the G34.
    The only 2 remarks I have is that you get some gasses in your face when shooting from a passive position (don’t have that problem when you move around on a range) and it get’s really dirty after let’s say 350- 500 rounds.On top of that the stock is not adjustable but I am not the owner of a Viking size torso so I can’t really comment on that.

    Best Regards,


  7. TomcatTCH says:

    I have a Gen1 for a Glock large frame. I run a Glock 21 gen3 with about your success rate. It’s not the most reliable thing in the world.

    With the stock spring, my striker does not fall with enough authority to set off a primer. I have swapped the large red spring for two intermingled springs with a bit of success. I might have to try trimming a coil or two off of the stock spring though.

    It has promise, but it’s surely more annoying then it should be.

  8. Jay Hardy says:

    Update to my above remarks. I have run about 500 rounds through my Gen 1 KPOS with a Glock 19 and haven’t had a single FTE. I now have 3 SBR’s , the KPOS, a Masterpiece Arms 9300, and a 300 blackout, and the KPOS is by far my favorite.


  9. Dneuzil77 says:

    I don’t want to ask an amateur question here, but have you thought about getting a longer barrel for the Glock 19 that you have dedicated to your KPOS? If the pistol is dedicated to the enclosure anyway wouldn’t/couldn’t the longer barrel increase accuracy at range? I would think that you would want a little more accuracy since, how I understood it, this was an alternative to a rifle caliber weapon system. I do understand that a longer barrel could cause mechanical or even loss of velocity with the round but I figured you’re the guy to ask.

    Your loyal follower

    • CR Williams says:

      Up to a certain point a longer barrel will actually increase velocity, not degrade it. A site called Ballistics By The Inch will demonstrate this and show where it begins to fall off with both longer and shorter barrels. They have charts for 9mm rounds.

    • Short Barrel Shepherd Short Barrel Shepherd says:

      Hi there! Not an amateur question at all. If the rest of the system was working well I’d definitely try a longer barrel. However, Glock barrels past a certain length (usually 6″, but depends on the frame) are rumored to have lockup and reliability problems. Since my enclosures already have problems I didn’t want to add another element into the mix. Thanks for reading!

      • Dneuzil77 says:

        I see your point. I mean watching your videos you haven’t seemed to have issues with engagement ranges so it’s probably a moot point. I have been really satisfied with my Glock 19’s capabilities out to 50 and even 60 meters. Thanks again for the insight and information!

  10. CR Williams says:

    If you’re going to go beyond G34/35/41/17L barrel length I would suggest ditching the idea of enclosures and looking at carbines and AR-pattern pistols that run Glock magazines. There are more available now than ever. Do avoid Just Right carbines, as they are not fighting guns.

    • Short Barrel Shepherd Short Barrel Shepherd says:

      I agree, especially if the potential owner is in the United States. I think there is some value in enclosures if people live in countries that limit the number or type of firearms people can own.

  11. Dylan says:

    The issue you had with the fit on the pistol’s rail is common, as there is actually quite a bit of variation in the size of the rails between pistols on some polymer-frame pistols, like Glocks. The KPOS was designed to address that issue. The latch needs to be turned to latch toward the rear, never the front, and if it is too loose, the lock nut on the other side should be tightened until it is as tight as you prefer. Also, it should not be locked until after the pistol is swung up into place in the frame, and then it locks the pistol into place by the rail, and locks the lower half to the frame.
    The change in the spring plate for the weaker frame of the Gen 4 Glocks was made universal several years ago, and It’s too bad you never received a new one from Mako.
    As far as the issue you had with brass deflecting into the action, it is almost positively due to the spring-plate issue, as the stronger spring plate, designed for the Gen 3 Glocks, can cause the weaker frame of the Gen 4s to bend slightly and slow the slide travel of the slide, changing the ejection pattern. This was never an issue with the stronger G3 Glocks, or with any other pistols, as most pistols have more rigid frames that Glocks anyway.
    If I had one of the new spring plates I would send it too you, but I don’t – I run Gen 3s anyway, which I recommend.

  12. Joshua Bressel says:

    Let me say, I HIGHLY recommend the G1 KPOS over the G2. It is more compact, more reliable, and better designed. It is also less expensive. The problem you are experiencing with the charging handle is probably because it is adjusted too tightly. There is a “sweet spot” for the tension, on the grip, then you loctite it. I do have a Gen 3 G17, and have experienced ZERO malfunctions, EVER, with my KPOS, and he’s right. There’s no need to ditch your Gen 4, but I recommend a simple adaptor, available from Lone Wolf Distributing, that lets you use Gen 3 hide rods, and springs, in a Gen 4. It’s a simple bushing that will VASTLY improve your reliability. I also recommend, for concealment, the Colt sling bag, which allows rapid deployment of even a suppressed KPOS, on the back, and a G19 or comparable, on the front! Also, I recommend reaching out, directly to Israel, to Zahal, at Zahal.org, for the spring plate.

    SGT Joshua Bressel,US Army(ret)

  13. Drrere says:

    What do the letters “KPOS” stand for and what is the mechanism that allows the slide to be raked with the charging handle?

    • Short Barrel Shepherd Short Barrel Shepherd says:

      After trying to get mine to work, I think “KPOS” stands for something special to me 😉 I don’t know what it really means.

      The charging handle grabs the front of the slide, sort of like a fork.

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