I know the last time copper cases were used in the Army was 1876, after the battle of Little Bighorn. That was one of the reasons the troops had trouble firing back at the natives, because their single shot Springfield Trapdoors rifles couldn't properly eject the spent cases. A lot of the copper cases were stuck in the breach when the barrels got too hot, or ripped in half when trying to eject them, and since the carbines a lot were using didn't come with cleaning rods attached, they had a hell of a time digging those empty cases out.
When the Army when to brass cases, the ejection problem disappeared.
I am not sure when consumer ammo stopped using copper cases.