After seeing some cool videos on lost foam casting and also becoming addicted to Joerg Sprave's videos on YouTube, I decided that I had to try this method of metal casting. I used some StyroFoam as my foam material to carve into a slingshot and then put it in sand for casting. After pouring, it turned out quite well! It has a few pits and imperfections, but it looks pretty awesome otherwise. Although its rubber doesn't perform very well in the wintry cold, it should be powerful enough for squirrel hunting in the spring and summer. I look forward to blasting some stuff to tiny bits as soon as it warms up!
Also, check out its Instructable for more detailed information! If you want to watch the pour, check out this video and this ingot casting video on my YouTube channel. I have included a few pictures of the casting session (I also cast a few nice-looking ingots in the same session):