10,000 years ago people went from the stone age to using copper as the first metal weapons. I’m sure it can be done now at home. Solids have been in use for a long time, Barnes sells a lot of them. The metallurgy is better than plain copper but nobody will worry about that. Bullet design will change because copper is lighter than lead but not all that much.
Corbin reloading sells purpose built swaging presses and tools. http://www.corbins.com/ I don’t have one but I could build one with a 10 ton hydraulic jack that will get the job done.
Copper, Melting point
With modern fire brick & blower technology, existing smelting furnaces, ceramic kilns, there are to many ways to melt copper to list.
As for getting copper after shtf…..miles of wire over your head.