SigSauer M400 jam
With new rifle and twenty rds in new Sig 30rd polymer mag, about halfway through a the spent was ejected and a fresh round chambered but the bolt jammed about half open over a another round partially pushed out of the mag. The point of the jammed round was just short of the chambered round while the back was still below the mag lips. There was enough clearance to hook the rim of the chambered round and slide it back and out of rifle. 2102 Lake City 55gr fmj. Input from seasoned AR owners on malfunction welcomed.