Not trying to hijack this thread, but I just started reloading a batch of 5,000 5.56 milsurp brass that came from a military installation and it was all once fired (with crimped primers). I procesed the brass and started reloading it. In the first 500 rounds, I discovered four rounds that split at the neck when I was seating a Hornady 55 gr FMJBT bullet. I never have fired this brass.
The splits were longitudinally down the neck and partially around the circumference where the neck begins to flare out. These were all LC08 brass. Maybe there's a problem with that year's production?? The OP said some of his brass was LC08 also. Interesting.