I'm a big fan of Nerf, and have been ever since my brother and I began our foam-based sibling warfare as kids. My interest in Nerf has continued as I now use the guns for intense office combat. While I find the propulsion sufficient for battling coworkers, you should check out this article on someone who built a better blaster from the ground up. I've looked into modding mine, but this takes it to the next level. You can find info on the project here.
