Several billet makers are doing the tension screw in the lower now, and for awhile. Ones that come to mind are Spike's (their 5.56, and eventually 7.62, if the make it) and Mega. Seekins probably has it, since they made the Spike's billet uppers and lowers. I'm sure there are more, but those are the ones I have personal knowledge of. It's something that needs to gain in popularity, for sure. <thumbsup>