If I were to try to sling something inside what woud I use?  I'm thinking hacksacks.  I have some room outside, but i wouldn't like to hit a house  .  What do u think?

Hackysacks work well indoors, tho the small ones are on the light side (approx 1.5oz).    Advantage is that they have no rebound.   Still, I wouldnt want to repeatedly slam a 1.5-2.0oz Hackysack into unprotected wallboard.    Also, Hackysacks are expensive ammo.  

To avoid hitting houses (other than your own), you might want to use the vertical-underhand spin.   Easier to control direction, tho elevation is still a challenge.   

Start gentle.   The power will come later.  mgreenfield

Gee, that's not too bad for reuseable ammo.   I gotta look at Wal-Mart!   Any idea what they weigh?   Let us know how they hold up to the pounding.   Tnx!   mgreenfield

I've used those 'stress' balls, the ones they sell at office supply stores.  The soft foam ones don't bounce as much as a tennis ball, and there's not much danger of damaging anything unless you knock something over.  They're more expensive, but if you're slinging indoors, you can use the same one over & over.  The downside is that they're so light that they don't really give the same feeling that slinging stones does.

Somewhere in here is a post (I don't remember who wrote it -- maybe JeffH?) about making balls of yarn, like 'koosh' balls.  I haven't tried those yet.