Spent most of the last thirty years designing and fabricating copper (usually 11000) bus bar systems for everything from hydro dams and steel mills in the U.S. to oil pumping stations in Saudi Arabia & Kuwait.
Copper is copper, and if it's isn't, it's called an alloy.
That being said, I sure can't speak to just how honest bullet manufacturers are, I just assume when they say copper, they mean copper.