Making a sling shot and need some pointers...?

Question:Its a male mulberry tree branch if that matters. I already took the outer layer off of the sling shot. The branch was just cut today, should I wait a day or two then sand it down? Would funishing it stop it from splitting or what would stop it from splitting?

Answers:
I dunno. I bought a good quality one for 2 bucks. You can buy them anywhere for real cheap. Plus, you don't have to make them