I just put together a 6 arc using an Aero upper/lower and Ballistic Advantage 16' bbl with an adjustable gas block and got to shoot it yesterday. I had an ASC marked 6.5 Grendel mag, and it functioned fine. I also tried a Magpul PMag 10 rounder, and it worked fine also. No issues with either mag. I was shooting Hornady Black ammo 105 gr factory ammo.