That's the one.  It's in the museum at Moundville, Alabama. 
They've got a web site.

I think they are working on a virtual tour but I haven't been there since March, when they shut down.

actually coral sling stones are a lot heavier than you would expect.
Mine weighs around 70 gms.
And it would be like being hit by a cheesegrater rotating at 1000 rpm.

If you were throwing against someoine without armour - the coral 'stones' would be the most vicious !
You'd be looking at seriously nasty wounds.

Wow! Awesome collection man! Great to see artifact stones from other places..truthfully we have seen those same make of slingstones here as well. Some private collections have some very impressive inventory. Historically, slinging here was beyond weaponry, it was sport. Many of our ancestorswere buried with slingstones.several have been buried with more than 100 in each!

We are finding agreat variety not just in the type of stone, but also in very specified shape. worth the study for sure. Thanks for sharing