I was planning to post on here what a great job they did, because they sent a worked over upper back to me with a new rifle case, a new mag, and some other goodies, but unfortunately, it still has a problem, and CS seems to have dropped the ball a bit. The upper still can't cycle IMI m193 (which my M&P15 does just fine). Now I contacted them again multiple times and they haven't gotten back to me.
The gun will cycle wolf and tula, but it won't work with IMI m193. Initially I thought it was overgassed. The returned upper had a new FSB installed, and cycled much more gently, so I think they put a gas port plug in, or something like that - they never told me if they did anything. The brass comes out all torn up - although I'm not worried about that. The real problem is that the rounds are jamming at the bottom of the feed ramp. I had a high power shooter at our club take a look. He put some of his ammo through it, and it cycled just fine, and the brass came out ok. He thinks it might have a slightly smaller than SAAMI spec chamber. He said maybe it's throwing off the timing of the gun, and maybe getting close to a double feed. He told me to just shoot wolf and tula out of it, but I'm not happy to have a DD upper that I can't trust to defend my home - that's what I got it for, and it's supposed to be a premium product.