The crossbow was a leap forward to begin with, offering the ability to store the energy of the human arm, without needing to hold it in place. It was also more accurate than a bow. The Chinese did it again with the repeating crossbow. Whilst they weren't necessarily the first to come up with the idea, they did it in isolation and in one of the most advanced forms. The design was simple, a magazine dropped a bolt in place as the string was pulled back with a lever mechanism. These devices could fire a bolt every one and a half seconds. It doesn't sound like much but these were the machine guns of the day, offering unparalleled rate of fire. This did sacrifice some penetrative power. It's okay, though, they added poison sometimes to make up for it.