Review: CMMG 22LR AR Conversion Kit

Shelling out big bucks for .223 or 5.56 ammunition nowadays can be a bit overwhelming. You know you need to keep training, but, man, those rounds are pricey. So what do you do? How can you keep your shooting skills sharp without spending your life’s savings on ammo? Switching to .22LR has always been a money saver, but you have to buy a whole new gun for that. Or do you? What about shooting .22LR through your AR?

Wait, what? You can’t do that! Well, normally, you’d be right. You can’t just shove a magazine of .22LR into your AR mag well, send the bolt home, and pull the trigger with good results. But what if there was a way to convert your AR into a .22LR shooter and save a ton of money while still training on the AR platform?

The CMMG 22LR conversion kit quickly turns any standard 5.56/.223 AR into a .22LR training aid. (Image: CMMG.)

In the old days, if you wanted to train on an AR platform but not cough up the dough for the expensive ammo, you had to buy a separate rifle that looked like an AR but was really a .22LR. Companies like Smith & Wesson and others augmented their traditional AR line with .22LR versions that operated the same as the larger caliber big brothers but cost less to shoot. If that’s your thing, you can still get rifles like that. They do offer many benefits, including training on a familiar platform while saving on ammo. But thanks to Missouri-based CMMG, you’re no longer stuck shelling out $400-$600 or more for an AR look-a-like that’s really just a glorified .22LR.

The 22LR AR Conversion Kit does exactly what it says: converts your existing AR into a .22LR practice platform with a quick swap of the bolt carrier group. No more switching from gun to gun.

How does it work?

The CMMG AR Conversion Kit is super simple to install. Take out your rear takedown pin, remove your existing bolt carrier group, and slide the conversion kit into its place. Close it all back up and off you go! No more changes. That’s it.

CMMG 22LR AR Conversion Kit
The conversion kit replaces the bolt carrier group.

The kit completely replaces your BCG and works almost like it. I say almost because it does function slightly differently in some ways but is mostly the same. Some of the differences are internal, and you’ll never notice them. Some are external and might throw you at first but will quickly grow on you.

To convert the chamber from .223 to .22, the kit has a spent .223 casing permanently molded into the end. The fake round sits inside the chamber to direct the smaller caliber round accurately. Yes, they are almost identical but just different enough to need a funnel to direct the round into the barrel. This can cause a bit of a problem, but not always. More about that later.

CMMG 22LR AR Conversion Kit
CMMG engineered a complete stand-alone conversion kit, including a fake .223 casing to direct the slightly smaller .22LR round safely into the barrel.

The conversion kit doesn’t use the buffer tube in the stock for two reasons. One, there’s not enough recoil to need it (it’s .22LR, after all), and two, the kit has a built-in spring that works off the gas system to cycle the bolt within itself.

Shooting the kit is identical to shooting your standard AR with one exception: the bolt catch doesn’t work with it. But that’s really not a big deal because the magazine follower is tall enough to hold open the bolt enough that you’ll feel the lock back and know it’s empty. You’ll still charge the chamber the same as with the normal BCG, but the charging handle only goes back about halfway because that’s all it needs.

Mags & Ammo

As you might expect, the conversion kit requires different magazines, three of which come in the package at 25 rounds each. They look like regular AR mags except for the top. Several manufacturers make .22LR conversion kit magazines, so you don’t have to use the CMMG-provided accessories, but while I didn’t test the kit with others, I assume the CMMG magazines work the best. At least, they worked fine for me.

As mentioned above, the traditional bolt-hold-open function is inoperable with the conversion kit installed, but that doesn’t mean you’ll be clueless when the gun is empty. The bright orange follower sticks up high enough that it holds the bolt open until you release it.

cmmg conversion kit magazine with .22LR ammo
Lesson learned: only use top-quality .22LR ammo to avoid stoppages.

While the magazines worked perfectly, they are not perfectly designed, in my opinion. I would like to see some sort of witness holes to know how many rounds are loaded. Counting to 25 is not hard, but it would be nice not to have to use all the digits on all four appendages and one from the neighbor. Even a single slot at the 25-round mark would be nice to confirm it’s full. Also, these mags are a bit more difficult to load than traditional .22LR mags. Not sure exactly how to solve that, which is why I’m not an engineer, but I bet someone smart at CMMG (there are a lot of smart folks there) could figure it out.

If you’ve shot .22LR long enough, you know two things about it that most accurately describe the typical small-caliber shoot experience. First is that .22LR is notorious for being a dirty round. It creates a huge amount of carbon for its size. It’s hard to imagine how such a small round can make guns so dirty, but it does. The second is that .22LR hates shooting out of a dirty gun. Ironically, the same caliber that hates the dirt creates the dirt.

Compounding the challenge is that shooting .22LR out of a .223 barrel is a mismatch, so it’s shooting out of a gun it’s not designed for. All of these factors resulted in a very disappointing first time out with the kit. About a third of the rounds jammed, misfired, failed to feed, failed to eject, etc. Frankly, I was shocked. I expected some level of poor reliability because .22LR by nature is unreliable. It’s one reason you should never carry it for self-defense. But I didn’t expect it to be this bad.

CMMG .22LR conversion kit magazine with CCI ammo case
The conversion kit’s 25-round magazines do a great job with only a few minor complaints.

Two factors contributed to the bad outing, both my fault. Since the conversion kit was straight out of the box, it was not sufficiently broken in. The recoil spring was tight, causing the system to not work as efficiently as it was designed. Also, I was using cheap bulk-pack ammunition, the kind you can get for cheap because it’s cheap. It caused all sorts of problems, as chronicled above. After the initial break-in period of about 100 rounds and getting wise to the bulk ammo issue, I switched to CCI Mini Mags, and the experience from that point forward was night and day better. The system cycled properly with far fewer stoppages and much better shooting consistency.

When I got it home, I cleaned it out of habit and because I wanted to see how dirty it got. As expected, it was filthy. I ran a bore snake through the fake chamber cartridge, and it came out black and powdery. The entire unit was caked in ugly carbon inside and out. However, a little rubdown with gun-grade solvent did the trick. Soon, it was squeaky clean. Most calibers don’t require regular cleaning, but I recommend cleaning the conversion kit after every use to keep it running smoothly. It is a .22LR, after all.

I took the conversion kit out several more times over the following weeks—for science, of course—and had much better luck. Breaking it in and changing to better ammo did the trick.

Overall Impressions of the CMMG 22LR Conversion Kit

While my relationship with the CMMG 22LR AR Conversion Kit got off to a rocky start, it got much better once we figured each other out. If you want to save a bunch of money and not have to buy two guns, this AR conversion kit is the way to go. At just $229.95 for the drop-in BCG and three 25-round magazines, it’s a whole lot less expensive than an entire gun. And it lets you train on a rifle you’re already familiar with. My recommendation? Order yours today.

David Workman is an avid gun guy, a contributing writer to several major gun publications, and the author of Absolute Authority. A logophile since way back, Workman is a quickdraw punslinger and NRA RSO and Certified Pistol Instructor. He helps train new shooters on basic handgun skills and CCW requirements and is a strong advocate for training as much as practicable. "Real-world shootouts don't happen at a box range."

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