thought that people here might find this article interesting ...
http://technology.newscientist.com/article/dn14372-toy-rocket-inspires-variablespeed-bullets.html
A gun that fires variable speed bullets and which can be set to kill, wound or just inflict a bruise is being built by a US toy manufacturer. The weapon is based on technology used to propel toy rockets.
Lund and Company Invention, a toy design studio based near Chicago, makes toy rockets that are powered by burning hydrogen obtained by electrolysing water. Now the company is being funded by the US army to adapt the technology to fire bullets instead.
http://technology.newscientist.com/article/dn14372-toy-rocket-inspires-variablespeed-bullets.html