What about using small water balloons in sling tag?  They are heavy enough, and would break on target.  They are cheap, and would be much safer than any type of ball worthy to be slung.  I haven't seen them mentioned yet on this forum.

Banzai wrote on Jan 12^th, 2015 at 12:03am:

What about using small water balloons in sling tag?  They are heavy enough, and would break on target.  They are cheap, and would be much safer than any type of ball worthy to be slung.  I haven't seen them mentioned yet on this forum.

I like the idea in theory. Though they would have to be filled and tied very consistently or it would affect accuracy.

Actually, you could probably make "spherical gelatin capsules containing primarily polyethylene glycol, other non-toxic and water-soluble substances, and dye."  Essentially, giant paintballs. 

I've tested actual .68 caliber paintballs.  The range was less than stunning but I think if we made them bigger, it might work.

not a bad idea, altough i would use something that doesn't go away.. we've used tennis balls and i hardly think they could be beaten. very safe,altough they can hit quite hard up close and if slung hard. Readily available, can be relatively cheap, reusable consistent shape and size.
Decelerating rapidly.

I guess it depends if you play it with a paintball mentality or a NERF mentality, on the ammo reusability thing.   ;)  But that is also due to the fact that I have never slung tennis balls.

On a closed football field for example, you can do a nice lil slingtag battle with ~10 tennis balls, and no need to carry 500 one use ammo and fill everything with garbage. pros and cons of course