I have two of their dedicated 22LR uppers. The difference between their 22LR upper and a 'real' AR upper is the barrel, barrel collar, bolt, receiver plate, recoil spring, and 22LR magazine. The mags they use aren't proprietary, and can be had for as little as $12 each these days. The cool thing about their uppers is that the barrel sticks into the receiver (the barrel collar surrounds this part of the barrel) so that a 16 inch barrel looks like a 14.5 inch M4 barrel when the rifle is assembled. The other nice thing is they use a M4 profile barrel on their 22LRs; I've never got mine even hot to the touch. I'd probably have to buy a 50 round drum and rapid fire it to do that.
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The first one I and the wife bought about 3 years ago at a gun store, so I have no idea when CMMG made it. The gunstore had paired it with a RRA lower. The bolt, receiver plate, and barrel collar in that one were parkerized, and it only really liked Federal and Winchester ammo. It was a jammomatic with Aguila.
That upper still has iron sights, but I've replaced it's bolt, receiver plate, and barrel collar. The original receiver plate came apart and the feed ramp on the original barrel collar got all scratched up. CMMG has made quite a few updates to their bolt since I bought that thing 3 years ago, and it now runs with every type of 22LR ammo I've tried.
I got a second 22LR upper from them about a year and 1/2 ago, that one I ordered with the stainless bolt, receiver plate, and barrel collar upgrade. That one now wears a Burris 2-7x scope so I can just switch between the two uppers if I want to shoot scoped or irons. The second upper came with their newer bolt and ran complaint free right away with all 22LR ammo I've tried.
Both uppers now run nearly perfectly. They routinely go 1,000 rounds + between malfunctions, but I also clean & oil them between every range trip. Come to think of it I think the first malfunction my scoped upper had was right about 3,800 rounds after I bought it, when the firing pin broke in half. Luckily they sell all the individual parts on their website so I was back up and running for $15.
Accuracy wise the best I've done at 50 yards was a 5 shot group the size of a quarter [as in 25 cents, not 1/4 inch]. I rarely shoot 22LR past 25m though, I've got a bunch of targets I print off that simulate range and are meant to be shot from standing, kneeling, sitting, & prone as the simulated range increases. For that type of shooting the upper is far more accurate than I am. I took the scoped upper to an Appleseed shortly after I got it and it managed a 214 score in spite of me.
I've got right about 17,000 rounds through the two uppers now and my only complaint is with how much they charge to ship a dang firing pin.
Eventually when I make more money than I do currently I'd love to have a 50 round drum or two and a suppressor for those uppers. They have the standard threaded barrels.
