Re: LC brass question
Mil-spec ammo has crimped primer pockets, while civilian cases do not. That said, ATK runs Lake City Army Ammunition Plant (LC headstamp with year of manufacture), and uses LC brass for some of its civilian loads (American Eagle, TRU, etc.). My guess is that the brass you have is from a civilian ATK load that does not crimp the primers in Lake City brass.
I guess it could have been a military reject load that failed to pass inspection because of the lack of crimped primers.