alt Hacker NewsA naive estimate of accuracy is that, at a rotation speed of 5/sec (1800 degrees/sec) a 1 ms error in release time causes a 1.8 degrees aim error, or 3 yards at 100 yards. You could hit the broad side of a barn, but not a buffalo.
But humans can’t reliably time things to 1 ms, and good slingers aim better than that, so there’s more to the technique than the naive version.
You assume the stone is released along a circular path, but that isn't quite right. When you release the stone you extend your arm forward, changing the arc of travel.