I see the .577 mentioned with hollow mono bullets, are they any good?

I've also heard that copper and BP is a bad combination for the barrels, how can those bullets be used In let's say an old .577 3" hammer double? Is NfB a bad idea in such a gun?
What is the option on bullets if one would like to hunt Ele with a 8 or 10 bore gun? Only shots to the body, or headshot ok? I'd very much like to hear some experiences?