There were some tests conducted many years ago (1958 or prior,) at the Frankford Arsenal. I still have the "Shooter's Bible" where it was published. Haven't read it in years, but what they did was to take new brass, one group sample kept indoors in controlled conditions and not exposed to ambient air. The other of the same batch was put on the roof of the arsenal. After a long period of time the new brass exposed to ambient conditions, was cracked and corroded. The admonition of the article was to keep your brass in Ziploc bags, or at least out of ambient air where pollutants exist.
