I know this doesn't belong here, but some of you might be curious about their retrofit kit.
I ordered my CMMG gas piston kit and upper during election day last November. This is my set up...
16" CMMG upper receiver
CMMG gas piston kit
MATech rear BUIS
MI front BUIS (rail height)
MI MCTAR-20P rail (this rail is designed to clear the piston system)
Bushnell holosight (EOTech knock off)
Since I've had it, I've been to the range a handful of times. Keep in mind, I'm doing this off memory and most of my data is a few months old.
Pros:
$450 at the CMMG website (not sure if the prices have changed)
I especially liked how it came with it's own bolt carrier.
Pretty simple installation: If you know how to remove a gas block, you can do this. I actually took off my barrel completely since I didn't want to cut my delta ring for the rail system.
Being able to service the piston from the front with just an allen wrench.
That being said, there aren't many parts to it. Once disassembled, there is the plug, washer, piston, and spring.
Easy to service and clean the parts.
Can go approximately 1500 rounds before cleaning (haven't tested this since I just clean it every time)
Cons:
There is some buffer tube wear like other retrofit kits. It's rubbed off the finish inside the buffer tube, but it hasn't gouged out any metal. After I put another 500 rounds through it, I'll get back to you on how bad it really is.
Parts need to be replaced...after about 7500 rounds, it's recommended to replace the piston return spring. It's not a big con, since you'll probably need to replace other parts after that many rounds through your AR.
At the time it was only available for 14.5"-16" no mid-length or rifle length. Not sure if that has changed.
Weight, but all the gas piston kits and rifles weigh more.
Since I've installed it, I've fired about 500 rounds through it. Unfortunately I've never fired the upper in its original form to make any comparisons. I can tell you that I haven't had any failures what so ever, not even from the magazines. I've tested American Eagle XM193, PMC, and Remington all 55gr FMJ. From the standing with a modified hasty sling, I was able to keep all the groups under 6 inches at 100 yards using the Bushnell which I find acceptable in that shooting position. I also didn't have a problem hitting metal silhouette targets out to 600 yards from the prone using the BUIS. I doubt that the MOA has changed much from the original direct impingement configuration.
All in all, it's a tidy system. If I could do it again, I probably would. I am very curious about the Adam Arms kits in other lengths. That's probably because my other two ARs are 20". In the summer I will be putting together another 16" with the Adam Arms kit for one of my friends. I'll be able to make a better comparison then. Another thing I'd like to add is that the retrofit kits, as awesome as they are, aren't the same as native gas piston uppers like the LWRC M6. I spent nearly the same amount of money on my upper, piston kit, and rails. I could have gone with LWRC, but I like knowing my rifle inside and out.
These are some pictures from last December. The rifle hasn't changed much since then. I added a light and pressure switch, but that's it. Sorry for the low res.
http://i59.photobucket.com/albums/g296/skyungjae/Guns/FK416/Picture002.jpg
http://i59.photobucket.com/albums/g296/skyungjae/Guns/FK416/Picture004.jpg
http://i59.photobucket.com/albums/g296/skyungjae/Guns/FK416/Picture005.jpg
http://i59.photobucket.com/albums/g296/skyungjae/Guns/FK416/IMG_0026.jpg