I guess no one knows the answer to my first question. I even called several distibutors and could not get a clear answer. Be that as it may, I am planning to install a Vltor tube (at least it should be stronger than my stock plastic tube). My question is the Vltor is a 5 position tube whereas my stock tube is a 6 position tube. Am I giving up "extended length" by going with a 5 position? I usually extend my stock at all the way as I have long arms. Thanks.