I was changing out my handguard and needed a new gas block, so I bought this one, seeing as it was the only one in town. I didn't foresee there being any problems until I attempted to slide it over the barrel to its final position. The cerakote inside prevented the block from sliding into position. I had to use a rotary tool and a stone grinder (after a failed attempt with a sanding drum) and remove about .05mm of cerakote to get it to fit. After the correct diameter was achieved, I then attempted to insert the gas tube and, wouldn't ya know it! That wouldn't fit, either. Had to grind away inside of that as well.
Eventually, with some warranty-voiding modification I was able to get it to work. Won't go down the road of buying CMMG, ever again, though.