Summer 2020    events include:  javelin, shepherd sling, marathon, water bag relay, and more!      Sling accuracy at 20m.  also distance challenge,  and speedloading!

Aye! should be good! We use 160 gram lacrosse balls, so with bounce and roll we cast ~300 yards! Being round, they fly quite straiqht! I practice 30 yards from a concrete wall, a perfect shot lands back at my feet. We wanted to avoid metal weapons, but axe throwing is popular in bars here.

for distance, would make more sense to measure to where they initially land - no idea what a lacrosse ball is like. But that would be pretty easy with tennis balls.

With bounce and roll, you'd probably be best off with a moderately long sling and a really good underhand throw as the spin of the ball would then work to your advantage.
Though would depend on the terrain as well.

Sounds excellent though - any idea on the sort of numbers of competitors you expect to get ?

Is there a flyer or any more information?

PM sent.  I am not too far from Colo. Springs.  Do you need hep organizing this?  Have you considered adding archery?  Maybe a Paleo-Decathlon?