Copper 42 Berdan

I picked a round of .42 Berdan this weekend that looks to be made of copper. No headstamp but looks the same as the UMC rounds. No paper patch on bullet. I thought that I had seen a reference to copper cased rounds of this before, but now can’t remember where I read this. When I look closer, it looks like the bullet has traces of copper on it also. Could this be real or did someone coat a regular brass case with copper for some reason?