CMMG .22 LR AR-15 Conversion Kit Review

    The days of blowing through a case of .223 ammo ended for a lot of us some time around the last presidential campaign. Until that point, the ammunition had been relatively affordable.

    Even though prices have backed off the historic highs of the ’09 buying frenzy, .223 rounds are not as cheap as they once were. Also, double-digit inflation in ammo pricing is now a reality thanks to the increases in the metals markets.

    Thank goodness for the .22LR, eh?

    Several companies offer .22LR conversion kits for the AR15 platform. One of the most affordable kits is offered by CMMG.

    The Kit

    The CMMG kit I tested came with an entire bolt assembly replacement and one magazine. I also picked up a second magazine (also known as pure evil…more on that later.)

    The kit comes with easy-to-follow directions, which you probably won’t need anyway. To install the kit, you simply remove the old bolt carrier and install the CMMG carrier. It takes all of 10 seconds to accomplish.

    A few notes about the kit. First, the CMMG conversion kit is designed for 5.56 chambered guns, not .223 chambered. Most of the AR15 rifles I have ever seen are chambered for the 5.56, but make sure yours is before running off to buy one of these kits.

    Second, make sure you remove the green rubber end cap from the end of the conversion kit before installing. This should be obvious, but I don’t want anyone trying to jam the thing into your upper.

    Last, this kit works for direct gas impingement guns only – no piston guns.

    There are a few other suggestions for accessories not to use for best performance at the CMMG page. You should check those out before buying.

    Range Time

    The .22LR is a light shooting cartridge. Just how light struck me when I started firing them out of my AR.
    I had been shooting 55 grain Remington FMJ in a DelTon AR15 for a good part of the afternoon, when I broke out the CMMG conversion kit. When I pressed the trigger for the first time, I just started laughing.

    No one can describe the recoil from a .223/5.56 as “harsh” or “punishing.” But when running .22LR from the same gun, the absolute lack of recoil is amazing. If you have someone that is very recoil sensitive, and even the .223 is a bit much for them, get them started with a .22LR conversion kit.

    I ran both Winchester and Federal rimfire ammo through the rifle, and both gave average results at 50 yards. The AR15 I was shooting was sighted at 50 yards, and with .223 ammunition, produced tight groups.

    Both .22LR loads shot low by several inches, which was not surprising. Groups were not tight, with rounds striking in roughly a 9”-10” circle. The Winchester loads were the most scattered, while the Federal rounds were slightly more consistent.

    Neither load would have been suitable for taking a rabbit or squirrel with any degree of confidence. If I was planning to try to use the gun and conversion kit for pest control and varmint sized game, I would definitely have to try several different premium loads to find one that was much more accurate.


    The CMMG conversion kit was reliable with one magazine, but completely unreliable with the second.

    The magazine that shipped with the kit was very loose when seated in the gun. It would wobble in the magazine well, but seemed secure. Though I had my doubts, this magazine proved very reliable. I experienced only one malfunction with this magazine: a double feed after the first three rounds fired. After that, it was 100%.

    The second magazine, however, was the exact opposite. This magazine was very tight in the magazine well, and had to be forcibly stripped during just normal mag changes.

    I experienced nothing but problems with the second, tighter magazine. With this mag in place, double feeds were the rule, not the exception. Of the 26 rounds held in the magazine, I experienced at least 10 double feeds per load.

    After two magazine loads of pure fail, I just stopped using that mag and enjoyed the shooting.


    At about the same price as 500 rounds of US made .223/5.56 ammo, you can pick up the CMMG conversion kit and 500+ rounds of .22LR to feed it. At that point on, you’re saving about $140+ on every 500 rounds fired. So, from a pure nickels and dimes perspective, the conversion kit makes a lot of sense.

    For me, the drawbacks to the kit center on reliability and accuracy. With the right magazine, the kit worked fine. However, with the wrong magazine, the kit was unusable. I suspect that I could have made the tight fitting magazine more reliable with a hand file or Dremmel tool, but I shouldn’t have to. If I buy your product, I expect it to work.

    Accuracy is more of an open question for me. Some of the finest rifles in the world will give crappy groups with excellent ammunition from one manufacturer, and beautiful groups with ammo from another manufacturer. It is one of the great mysteries of life.

    I suspect that the AR with conversion kit will produce tight groups if I experiment and find the right load(s). It would certainly be a fun process seeking out the best loads for the kit.

    At the end of the day, I think the kit is a worthwhile investment as long as you know the potential downsides.

    [ Richard Johnson is a gun writer, police trainer and really bad joke teller. Richard also writes for Guns, Holsters & Gear, Human Events and BlueSheepdog. ]

    Richard Johnson

    An advocate of gun proliferation zones, Richard is a long time shooter, former cop and internet entrepreneur. Among the many places he calls home is