If the brass you found is a dull silver color, it is not brass but steel cases that were plated with a zinc compound, if I recall correctly. You can determine if they are steel by checking with a magnet.
Evansville Ordnance Depot loaded steel cased .45 ACP during WWII and somewhere I still have a box of EC 43 steel cased empties stored. I recall some informattion that was published in The American Rifleman many years ago (1960's?) that explained the use of steel cases by Evansville Ordnance Depot.