I have a Gas Piston AR set up. Suppose to be a DD light weight barrel bought from a known DD distributor (Barrel has not markings on it) with and Adams Arms Gas Piston Kit in a YHM Upper Receiver. Rounds out of my preban aluminum colt mags jam after the initial bolt release. Rounds load from my DPMS Plastic mags, however rounds ejected are heavily dented on the neck from either mag. All mags load and function properly in my other AR's and do not dent the brass. Any ideas of where to go from here. The barrel and upper have M4 feed ramps and they are wide and polished.
I have attached a pic the dent which is occuring at the one o'clock position.