I also have a CCMG dedicated upper. Actually purchased as a complete rifle, with the idea of buying a separate 5.56mm upper. Love it. Also have the M&P 15-22... love it as well! The 15-22 will run longer without needing more oil to keep things moving, but both work well. I prefer my CMMG, as it weighs and feels close to the same as my other ARs, but the 15-22 mimics an AR manual of arms right out of the box.
As far as Bat Guano's issue with the bulged barrel, that is ammo related... obviously fired after a previous round lodged in the barrel... has absolutely nothing to do with the CMMG unit.
The only issue that I have had with mine was after I first got it, it would fire without the bolt being fully in battery. After it broke in and wore the phosphate coating down in a couple of areas, it worked fine.