True once fired brass can be told if it hasnt been through a ultrasonic cleaner. One fired brass will still have some bare brass down inside the case as were as multi fired brass will be all black down inside the case. Im sure this isnt a tell all method but there is some truth to it. Look at a piece of once fired brass that you know is once fired and then look at a piece that is multi fired and you can see a difference from the carbon on the inside. lee