Primary Arms had the Balstic Advantage 16" barrels on sale. I never liked the looks of the stainless barrel that came on it. Glad I had a standard midlength gas tube. The one from Armalite was about an inch to long. Ran 40 rounds through the new barrel. Functioned 100% with PMC ball and PPU 168. The flyers are my fault not the rifles. 95 yds 8 shot group.