I have invented steam guns in my head, which I translated to paper but due to safety and practical reasons I have no intention of building in the real world. In the world I have created they are effective weapons but the man-portable variety, with a backpack boiler are only good for short range pummelling attacks. They can break bone but rarely penetrate the skin.
Today I thought I would look to see if anyone else had built a steam powered gun, to nobody's surprise, Adam and Jamie of Mythbusters beat me to it.
They use a different method than I had planned out but the result is about the same, a quick-firing inaccurate semi-lethal weapon.
The video below shows a steam cannon with a barrel being fired, despite the fact that it's a simple garage-built gun it obviously has some power.
If the two could be combined then you might really have something, I think the confederate system they copied on Mythbusters was highly flawed in the way it flung the balls out. A system with a barrel is necessary for any kind of power or accuracy, but I do like the gravity feed system they used. Having watched these two videos I have to say I think my design would be feasible and it overcomes the shortcomings of each design (Mythbusters lack of reliability and massive size, the Archimedes style cannon's unpredictable timing and slow firing rate). I almost wish I had a workshop big enough to build one.
Just for fun, here are Adam and Jamie again, this is a short video of a household water heater with all the safeties disabled.
Steam rocket! That's one of my favourite bits of video from all the Mythbusters episodes I've seen.