Thanks for your thoughts. I did not tumble the brass. I treated these cases the same as I treat all my rifle cases.
I use 0000 steel wool to clean the outside and clean the inside of the necks with the nylon brush and mica powder in the Midway case neck lube kit.
Out of hundreds of lots of rifle brass over decades this is the only lot that this has ever happened to. I have plenty of loaded rounds of various cartridges some dating back at least into the early 1980's and I haven't seen this before.
I will add that I have used very little Federal rifle brass over the years. In the common cartridges I mostly use Norma or Winchester, or more lately, Nosler. Then some Remington and very little Federal.
