The name El Dorado does does sound right and there was a second iteration of Bell (maybe a relative?) in Nevada. They did make cases and lasted long enough into modern times to have a web site before deciding that they wanted to do some other defense work. I think they manufactured the drawn .43 Spanish HDS (Huntington) marked cases I have.
Rocky Mountain and the long gone CCC (Connecticut Cartridge Co.) both use an entirely different process: they turn cases from solid brass stock. I would assume that Rocky Mountain is using some sort of CNC equipment. Turned cases seem to be both heavier and more brittle than drawn ones, but we will have to take what we can get. I hate having the wrong head stamp on cases.
