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CMMG PDW .22 LR (9" Upper)
As I was finishing up my review of the CMMG .300 BLK PDW I realized that I really needed to stop being cheap and give the federal government $200 for the privilege of registering a short barreled lower with the ATF. The minute I slammed the AMEX and hit submit, I found a whole new world of guns to look at. Given that the .300 BLK upper had been such a good deal, I started at CMMG’s website. I quickly locked in on their MK4 PDW .22 LR, a nine inch barreled upper chambered in .22 LR . . .

A short while later, a box with an upper and no magazines arrived at my door. Another call, a few more days of waiting, and I had two of CMMGs proprietary magazines. During the waiting period, I test fitted the upper with the pistol lower that had come with the .300 BLK version of the same gun. The fit was perfect. Once I had magazines in my hand, I confirmed that this was truly a plug and play affair. Pop your old upper off, slap this one on, load up one of the 25 round mags, and go to town. And to town I went.

CMMG PDW .22 LR 9" Upper (courtesy The Truth About Guns)

Almost immediately, I started getting failures of all types. Several failures to eject, a couple double feeds and the one you see above – which has to be the most fun I’ve ever had stripping a gun apart in the sweltering heat. The gun ran fairly reliably – as long I NEVER touched the magazine. Rest the rifle on a table or put your hand on it and it became a jam-o-matic. Lube didn’t help, cleaning didn’t help, and screaming four letter expletives didn’t help either. Well, not the gun.

While I’m used to .22s being finicky, I felt that the PDW gave me extra bouts of trouble. Given that .22 LR is about the most fun you can have for high-volume range days, it became immediately apparent that the CMMG upper was not going to be occupying a place in my safe. I like my guns to be reliable (at a minimum). That said, I know some folks have standards different from mine, so I gave it an honest go at accuracy testing with the hope that it might be an astounding peashooter.

CMMG PDW .22 LR 9" Upper in situ (courtesy The Truth About Guns)

Uhhhh not exactly. The first time out, I was certain that I had a scope issue; my shots landed all over the place. I’d conveniently forgotten a toolkit, so I saved a formal accuracy test for another day with a different scope.

Figuring that some was good and more was better, I set up on the ground, prone, with a Vortex Diamondback HP 3-12 x 42, a Harris bipod, and enough sandbags to fortify a bunker. Using CCI standard velocity 40 gr .22 ammo, I took my sweet time squeezing that gritty trigger. And yes, all the mall ninjas were jealous of my style.

Accuracy test with CMMG PDW .22 LR 9" Upper (courtesy The Truth About Guns)

The results were, shall we say, less than stellar. What I had on my hands was a failure prone and decidedly inaccurate upper receiver. After swapping two different scopes around, and giving it a thorough cleaning with no luck, I called up my media contact for CMMG. And by called, I mean that I sent him an email laying out the problems I had and the details of the review I was going to write and several options. The first option, and easily the worst idea was to let me tear into the gun. The second, and marginally better idea was to tell me to pound sand. The third, issue a call tag and have it checked out at the factory. Naturally, they chose the third option.

Several weeks later, a knock at the door and the brown shirted man had a small box for me. Inside, an upper that looked very much like the other one, and two new magazines, a different color from the originals. I got a nice follow up email from the team at CMMG to let me know that they had found some issues, though there wasn’t a mention of what they found.

Back at the range, I was unable to make the gun reliably hiccup with a variety of different ammo including super and subsonic types. I also tried screwing a silencer to the end in an effort to get it to reliably jam up, and had no such luck. Over the course of 150 rounds on my outing with the new upper, I had perhaps five failures, mostly related to failures to fully eject. No matter how fast or slow I fired, I couldn’t reliably recreate them, and while this doesn’t represent stellar reliability by any stretch of the imagination, it does line up with my other .22 experiences, namely – they’re not perfect.

cci std



CCI Subs

Back on the line with a bipod, and an even bigger scope, I started working through some accuracy testing and found that things were much improved. This is still not the precision gun you might be looking for, but it does hold less than two inches at 25 yards, and in some cases shot down in the sub inch territory. That’s not astounding accuracy but it does mean that you can rely on the gun to hit what you point it at. With a silencer attached and a simple red dot, this is quite the fun range toy capable of eliciting smiles from even the crustiest among us.

Specifications: CMMG MK4 PDW .22 LR Upper

  • Caliber: 22 long rifle
  • Barrel: 9 inch”, 1:16 twist, medium taper profile, 4140CM
  • Muzzle: A2 comp., threaded 1/2-28
  • Hand Guard: CMMG RKM7 KeyMod hand guard
  • Receivers: Forged 7075-T6 AL M4 type upper
  • Price: $599.95 – (not much less on the open market)

Ratings (out of five stars):

Fit, Finish, Build Quality * * * *

On the surface, this appears to be a pretty well built upper. The same complaints I had about the finish on the 300 BLK version exist here: the coating is pretty weak and easily scuffed. However, the threading on the muzzle was right and the controls worked well.

Reliability * * *

The original iteration of this upper was absolutely horrid. I was unable to string together a full magazine without at least one failure, sometimes many more. After a return to the factory, it is better but not perfect. I still had sporadic reliability issues. I’ve never considered guns chambered in .22 LR to be reliability kings, so some of it wasn’t necessarily surprising. I’d venture to guess that it might smooth out over time, and I’m certain that the more mechanically minded among us might be able to polish and tweak in such a way that it purrs. That said, I was disappointed, and I’d hoped for better.

Accuracy * * *

The first iteration was, without a doubt, the least accurate gun I’ve ever tested. And I’ve tested the X-Caliber. A return to the mothership seemed to help, and fed the right ammo, CCI Standard Velocity in my case, it is respectably accurate.

Overall * * *

Judged on its merits, this is a pretty decent upper. I certainly wouldn’t get rid of it if somebody gave it to me. But thats the issue. At $600 for the upper alone, this thing is bordering on the luxurious in terms of price. There are two justifications for owning a .22 chambered AR. The first is cost savings. All things being equal, .22 ammo is cheaper than comparable .223/5.56. That said, my last purchase of .22 ammo was priced at right around $0.11/round. My last .223 purchase was in the neighborhood of $0.30/round. At a $0.19/round savings per shot, I’d have to shoot well over 3000 rounds of .22 to offset the cost of this upper, and that doesn’t factor in the optic I’d inevitably have to screw to the top. At those kinds of prices, I could just buy a couple thousand rounds of cheap plinking .223/5.56 and call it a day.

The second justification is that you like shooting a .22, and hey who wouldn’t? They’re fantastic training rifles, great for getting new shooters over to our side (especially with a silencer on the end). But if you were hell bent on getting a silencer ready, short barreled .22 rifle that was both reliable and accurate, you could just as easily get into another gun for about the same money including the necessary ATF paperwork. Unfortunately, the PDW upper seems like a very expensive solution in search of a problem.

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  1. I built a dedicated .22lr AR using a CMMG bolt and CMMG.22lr barrel. It’s a fantastic gun that runs better than the above and is way more accurate. I found that it runs better if you leave the bolt a little dry and use the Black Dog magazines…they work great.

    • I will echo Gabe’s sentiments, as I have done the same. I usually have failures when it’s a little too wet from cleaning, but after a few break-in rounds, it runs fine. I have had best luck with feeding with ProMag 22LR mags, but without the pulldown follower, they are a pain to load. I have used the BlackDog metal feed lip 30ish round magazines, and they work well, but not as good as the ProMag, but they are easier to load. My gun also seems to prefer the Federal Automatch ammo. I have had no issues hitting targets out to 50 yards or so.

  2. 3 of 5 stars?! TTAG has started grading on a curve. The write up explains in detail how this is a pice of junk gun, but it still scores 3/5. SMH.

  3. I have the Chiappa .22 upper on a regular lower. It had a few hiccups in the first two mags, and then has been flawless since then. I had a friend use it in a 3 gun type shooting match and it never once failed. This match usually finds the weakness in any gun. The price? $220 with two mags from buds on sale. Accuracy is about 2 inches at 50 yards.

  4. There seems to be an element of variability in .22LR ARs.
    I bought a gen1 Chaiappa upper for $200 on CtD. Came with two mags.
    I put it on a Polymer80 lower and bought inexpensive rear sight, red dot and buffer tube, mil surp slung and stock kit on eBay and a (mostly) polymer LPK from New Frontier Armory.
    The finishing of the bolt is ugly but the only failures with cycling were when I used Remington Golden Bullet. Any ammo labeled “high velocity” cycles just fine.
    Accuracy is fine as well.
    I think I paid less for the whole gun than the MSRP of this upper.
    Go figure….

  5. Yeah, about this modular thing. Maybe there is something to the kiss concept. Whether I’m at home or on the range I want my AR to go bang. I am not going to ponder over which Transformer to make Manufacturer’s have jumped on the modular band wagon with visions of UUGE military contracts. The result has been fundamentals like reliability, accuracy and a decent trigger are left at the altar of early adapter market share. ARE YOU LISTENING SIG? There is a reason the unwieldy bolt action emerged as the most preferred in the 20th century.

  6. Hmm
    I’ve got the CMMG conversion .223 to .22lr kit and it runs flawlessly.
    I haven’t checked accuracy as I consider it a cheap plinker.
    Going to have to recheck that.

  7. Who has so many 22s they can buy an expensive toy like this to start with!?! I can keep just my 2 fed properly.

  8. Aftermarket 22LR conversion uppers and slides are rarely any fun thanks to reliability issues.

    Cried once when I bought a factory Sig 522 SBR. Been happy ever since though.

  9. I see people talking about field stripping to unjam those charging handle jams all the time and don’t know why. All you do it drop the magazine, pull the charging handle back an inch with your left hand, then use your right index finger to hold the bolt as you push the charging handle forward with your left hand. The casing will drop right out.

    The mags do stink though. The Black Dog ones with steel feed lips are much better, just often out of stock whereas you can find the CMMG ones stocked for about $10-$12 at a couple places.

  10. I have one of the CMMG conversions that I run on my 223 Wylde barrel and it runs perfect. I noticed that it didn’t get very dirty so I decided to run it til it started acting up before a good cleaning. 3995 rounds later it hiccuped and I had to clean the bolt. It is the most fun I have when I am at the range burning rounds!!


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