I recently purchased a MAGPUL CTR stock for my 556. It has the same amount of play whether the friction lock is engaged or not. Magpul says the SIG tube is the probable cause. Another member on here had the same issue and bought an aluminum commercial tube and the friction lock worked well after that. I read somewhere (can't remember where) that the mil spec aluminum tube is forged where as the commercial aluminum tube is cast, making the mil spec tube obviously stronger. Are the mil spec tubes that are sold to the public still forged? If so I may sell the commercial CTR and buy a mil spec along with the tube.