My understanding (second hand/ hear say) is that RRA is not making short uppers/barrels to avoid the SBR issue until they get established and proper licensing (C2?) to deal NFA. You can buy a 16" and have somebody cut it for you. I would use Mike Klos, but he is really busy, or Socom Mfg, and Kurt's Kustom, as I have just taken possession of (2) .223 cans and need a couple barrels threaded myself.