This is the Rambone slingshot, designed by the crazy german, Jörg Sprave.

https://www.youtube.com/watch?v=MlG3P_wf-6E

He shared a STL file of the model, but it has holes in it and some other inperfections. Also its very high res. I cleaned up the holes, optimized the model a bit and made it a true solid.

You can get the original file here:
http://www.simple-shot.com/pages/build-your-own-rambone-slingshot

I have not printed this yet, bit I'm fairly sure it will print nice.

Heres how to attach the elastic band: http://www.simple-shot.com/pages/tutorials-diy

If you print it, please share your results.