There is one definitive test: take one cartridge, pull the wooden bullet and dump the powder; drive a plain steel nail into a board and polish the head; stick the case over the nail, carefully ignite the primer with a hammer and another nail, then leave the case there and wait a day or two and see what the nail looks like. If you live somewhere with high relative humidity, drive a second nail with a polished head at the other end of the board as a control.