CMMG AR-15 M4 .22lr Conversion Kit Review

Today’s post builds off my previous AR-15 A2 survival rifle post. If own an AR-15 and you accept the notion that practice makes perfect (who wouldn’t), you’re then faced with the daunting financial task of buying enough .223 ammunition to become proficient with the rifle. Enter the CMMG .22lr conversion kit for the AR-15. Lucky Gunner , a seller of bulk ammo, ammo cans, and more, sent me a conversion kit  to review.

Their shipping is fast. Here it is, still unopened:

But before we get too far, let’s first consider the WHY? Why would you buy a .22lr conversion kit? Obviously – to save money! You spend money to save money. If I stroll over to Lucky Gunner to do the math, this is what I see:

There is a 20 per-bullet difference in price between the .223 and the .22. $160 (the cost of the kit) divided by 20 cents = 800. You will recoup the cost of this conversion kit in 800 rounds. How many rounds do you shoot if you go to the range? 200? That’d be 4 trips to the range and the conversion kit pays for itself. Then it’s all savings.

Are there other reasons to buy a conversion kit? Yes:

  • if someone is new to shooting, the .22 is easy and fun
  • you’ll shoot more, because every time you open the box you won’t be thinking “ugh, that’s X dollars”
  • you’ll become a better shot, because you’ll shoot more
  • did I mention the .22 is easy and fun?

Here are all the items:

There are instructions, a magazine, and the bolt assembly. At the bottom of the long sheet is a diagram of the style hammer an AR-15 should have to properly function with this conversion kit.

Rounded hammer = good.

Notched hammer = bad.

There were actually two of us field testing this. Conveniently, we had two different hammers:

The rounded hammer is supposed to have fewer jamming issues with the conversion kit. Other important points to note in the instructions:

  • high velocity ammunition is recommended
  • expect minor jamming issues in the beginning as the bolt assembly breaks in
  • trim areas of the magazine so that it properly fits in the magazine well, right here:

The .22lr magazine functions fine with the AR’s magazine catch assembly. Here is a photo comparison of the parts:

You simply slide one bolt assembly out and slide the other one in. The ammunition used:

I bought new high velocity rounds (on the left) for this review. We put lubricant on the new bolt assembly and fired away. We used both my notched hammer and his rounded hammer.

I had no problems with my hammer in the first magazine of rounds. His, with the rounded hammer, jammed a few times and fired 2-3 shells with just one trigger pull. That was the first few magazines’ worth of ammo. The conversion kit went back and forth between rifles and we both had jams:

Remember: these early jams/issues are part of the breaking in process. By the time we fired all of the .22 rounds pictured earlier, if we were using the high velocity stuff, we had no problems. No jamming and only one shot per trigger pull. High velocity rounds + initial break in period = fully functioning conversion kit. While I used my notched hammer for this review and had it work fine, the directions suggest rounded for a reason.

My only problem with the conversion kit is that the AR barrel has a twist rate for the 5.56, not for the .22. A .22 should have a 1/15 barrel twist, not 1/7 or 1/9. This impacts accuracy. How much and is it enough to matter? Because it was so cold, getting late and the snow was up to my waist – literally – we didn’t test that. I know we were both hitting the target:

The conversion kit is slick, fun and saves money. If money is no object, you might prefer a designated upper in .22 caliber for appropriate twist rate; but that’s more expensive and pushes the time it takes to make your money back through savings on ammo.

– Ranger Man