Bruised
Wish I could give you a good answer. My hearing has declined a bit over the years. I do remember my DD's first visit home after being in college for four months----there was a definite buzz to her rise spin that I hadn't heard before.
I would hazard a guess that it is around 24+ RPM's.
Rick
Why isn't this grip used to throw a baseball 12-6 curve, which is really just an upside down riseball mechanically?