Hoppe's used to have nitrobenzene in it when I was a kid. It originally had 9 ingredients, which is where the 9 in the name came from. Regulators have seen to it that
only 5 remain now, and the efficacy has, alas, been reduced.
The modern chemistries really are better. If you want to just remove copper, KG-12 is about the fastest I've seen. Way faster than Sweet's or any of the other ammonia-based bore cleaners. The only problem is it doesn't turn green or blue, so you have to depend on inspection to be sure it's done working. Like Bore Tech Cu++, it is a chelating copper remover. Cu++ was not as fast in my test (dissolving 2 mils of copper plating off a steel jacketed ball bullet), but it does turn very blue and is also way faster than ammonia. Bore Tech Eliminator has some of the same stuff as Cu++ in it along with some of the same stuff that is in their C4 carbon remover. It just isn't as strong as either one is alone.
All those products are water-based and low odor. They have corrosion inhibitors that are very effective. I've let them dry out in a barrel in humid conditions with no sign of rust.
Slip2000 Carbon Killer is the fastest acting on old carbon cake. I have made the mistake of letting it sit on some Parkerizing for a number of hours, and it thinned it out, so I don't put it there.
This article on two of the above products is an interesting read, though it's a dozen years old, now.
Gunzilla is interesting stuff. I left some in a tired old '03's bore for six weeks one time and it dissolved not only all the old carbon that was glazing some hidden ancient pitting, but also the rust in those pits came completely out leaving shiny bare steel. The carbon and rust was a sludge at the bottom side of the barrel that wiped out with one dry patch. It takes longer than Slip2000 Carbon Killer, but can do an impressive job. The original formula does not attack copper very aggressively, but I haven't tried their copper removing formula.
For lead, Sharpshoot'R, makers of Wipe-Out foaming cleaner, make a product called No Lead. You put it in the gun for about an hour and the lead converts to a sort crumbly gray-black material that just patches out. No brushing required.