How can you be a shooter and not know about the 45-70? That's a bit tragic.
Anyway, the 45-70 was developed for the 1873 springfield trapdoor rifle. The full designation was the 45-70-405 which meant 45 caliber, 70 grains of black powder, and a 405 grain bullet. Today, the bullet weight can vary from 350gr express type loadings to 500gr long range loadings, but the powder of choice is still black. Some people load them with smokeless but they have to jump through hoops to fight the large capacity and I've never seen anybody shoot long ranges with the cartridge loaded with smokeless.