I've also been thinking about gunpowder. I know you don't want it in the game, but I'm going to push this anyways.

This is the Shingicheon Hwacha

http://img9.exs.cx/img9/7876/hwacha.jpg

It basically shoots arrows so it's not like cannon balls or anything. The way I see it, it's like a massive Firelance. Just a thought.