A good reason to sort and identify your range pick up brass at least once so you know which headstamps are berdan and boxer primed.
Another 5.56 brass to watch for is Guatemalan surplus. Its boxer primed but has both undersized and lots of off center flash holes. I broke a couple of pins with it and decided to scrap what spent brass I had left and will leave the rest of the brass at the range when I fire up the rest of the factory stuff in the future. Not worth the aggrivation or expense involved, I rather reload Wolf steel cases.
I'll post the headstamp details on it tomorrow.
EDIT: The headstamp on Guatemalan surplus is IMG
Is this the headstamp pictured for your berdan primed stuff? I've seen lots of it around on the ranges and I think it might be the South African stuff that was prevalent several years ago.
View attachment 32549
It was easy to pick out because of the sparse stamp and the primer sealer color which was purple..ish.