I've heard that hailstones on very rare occasions have grown to the size of grapefruits!!
Every time I see large hail, a tornado is usually close by.
A while back in Colorado we had grapefruit/softball sized hail in one part of the state. It did some nasty damage. It's also very bumpy and not smooth. The smaller hail clumps together to form the larger ones. I had a bunch of golf ball sized hail in my freezer until I moved too far for them to stay frozen.
One time, when I had no idea a tornado was close by but there was a lot of hail around, I was happily skipping around the park collecting it. I wish I knew about the tornado, because I would have liked a picture of it. Apparently it touched down about a half a mile from my old apartment complex (I would have had a direct view of it).