I cut the ball off of a 2 inch tow hitch (like off of a truck) it is heavy and obviously solid I plan to throw it from my sling on my next outing, I will let you know how it works. any one else try anything along these lines?

tow hitch ball is usually between a squash ball and tennis ball in size - shouldn't weigh much more than a pound if that.
Shortish sling and some oomph should get it  afair distance :-)
I've slung rocks over a pound over a hundred yards.

Sidearm is probably best as it puts least stress on your shoulders and elbows.
Sling a decent sized rock within a wodland - what I call a brush cutter - goes through branches like they're not their. And for you eco nuts - mostly dead wood :-)

well I did it it didnt fly all that far or very fast however it sure did have a solid impact. I used an underhand throw from 20/25 feet into the side of a wooden storage unit on a friends property and it sounded like a gun shot when it hit.

I will try that. also since I now have three of these hitch balls I am thinking of making a bola out of two of them does any one have any words of advice?

did that a couple years back they work pretty well, they also very in size and shape  they are a impressive short range ammo