I want a few different uppers for my AR. I want to build an "urban sniper" rifle in either 6.8 SPC or 6.5 Grendel. And I am dying for Rock River to finally start making the .40 AR. I'm going to get one and SBR it when they do. I emailed them a week or so ago and they said they're still trying to work out an issue with the magazines..... And lately I've been looking hard at the Kel Tec RFB and one of those "pistol" versions of the Russian PPS 43 subguns they're importing now in 7.62x25. If I get one of those I'd want to SBR it also. Just because.