I thought I'd give a range report for the CMMG .22lr bolt conversion kit. This unit replaces the BCG (bolt carrier group) on your AR15.
I'll start off by saying it was worth the money and I can't wait to shoot more.
I experienced some break in issues. I stress that they were break in issues because they disappeared after 50 rounds. The bolt comes with a 25 rond full size magazine. I purchased two more with my initial order.
CONs: The magazines are hard to load. Part of the problem is the way the lip of the magazine is consructed. Those .22lrs are slippery when you're trying to push down your 20th round. I couldn't get them loaded up to 25 and I figure I'll be able to with some further use.
For the first 50 or so rounds, I had FTE issues. It would fire a round and the shell would get caught in the bolt tube in the strangest way. At times, it would try to double feed. I'll admit, I expected some issues so I wasn't too surprised.
I have a Plum Crazy Lower and the magazines do not free fall eject when the magazine release is pressed. In fact, I have to tug them out of the lower receiver after emptying the magazine. In all reality, this isn't a huge issue with me. I don't plan on using .22lr for a tactical situation and I don't forsee the need to drop a mag while on the run.
PROs: I worried about accuracy, but using open sights, I didn't notice a substantial difference while shooting standing (compared to my 5.56 rounds). I did have to compensate a bit on the sights to place the shoots where I wanted them. This conversion would work well in a small varmit hunting situation.
It is a pleasure to shoot .22lr out of an AR. The kids and wife are going to love it. I just need to get one of those $5 parts that take the "twang" noise after each fired shot out of the buttstock and this little rifle would be perfect.
As a side note, this was my first time using the range at DFW Gun Range and I like their service. They even allow double taps which is the first range I've been to in TX that allows this. While that may not seem like a big deal to you, it makes me think they see their customers as adults and not special needs firearm handlers. I was able to do double tap drills without fear of the loudspeaker!
hope this helps.
credit for answer to Texas Gun Talk 4/13/11