Were these original factory rounds? If so they probably were loaded with corrosive primers, which are worse than black powder for their destructive/damaging properties.
Most all the BP cartridge shooters I know of (myself included) take a jug of soapy water to the range with them and drop their fired brass in it immediately. When I get home I shake the jug vigorously, dump out the dirty water and put them in fresh water with just a drop of soap (I use Simple Green) then scrub them with a brush, inside and out. Another rinse with clean water and spread them out to air dry. In the desert where I liove that doesn't take long.
YMMV,
Dave