FYI. I just received a defective Magpul CTR. And the reason I am posting this is because I wouldn't have realized it if I didn't own a sling with plug-in QD swivels. The defective part was the QD swivel sockets. They were not machined properly with the groove on the inside to allow the ball bearing detents to engage. I could have used this stock for years and then tried to plug in a sling and been screwed. So if you have bought one and not checked this, I suggest checking yours. I have about 4 others with no problems, so maybe it is a fluke. Fortunately I purchased mine from a reputable vendor and I caught the problem the day I received it, so an exchange the first of the week shouldn't be an issue. Anyone else had this problem, or just unlucky me?