The best buffer tubes out there - Vltor REA5 A5 Receiver Extension RE-A5 M4 Aluminum Black

I've purchased multiple Vltor buffer tubes, both carbine length and A5-lenght over the years. With all of them, the stock fit is tighter than many, the finish is flawless, and there are never any dimensional issues. Plus you are getting a 7075 tube. They are well worth the price.