Contact the Manufacturer of the ball... They should tell you, "Yes, at xxx°" as everyone has a different rule, or just "no we don't recommend it"
Brunswick Loaded Revolver - 120° MAX according to Brunswick
Hammer Viral - Hammer Did not recommend, said only the vibrating water thing I have tried to put this ball in the oven at 120° and never, ever got any oil out of it, I just sand/polish it now.
120°F feels Warm for most people and is not too hot to touch. If My cooker reads 120°F my laser non contact thermometer reads 120°F so I am sure it is right, and I have never needed gloves to remove the ball... When heating other things Usually 135°-140°F is when things become a little to hot to handle, it will depend on you and what you are used to. And it will depend on what is being heated, the thermal transfer of a resin, plastic, or urethane to your hand is not as severe as the heat transfer of a piece of metal, so not everything feels the same at the same temperature.
If you over cook them with too much heat, you can do a few things, 1) you can age the plasticizers in the cover, 2) you can break the bond between the inside and outside materials of the ball. 3) I have read you can melt the inside of the ball. 4) You can crack it.
Normally, in my experience cracking occurs if you heat it up too fast and unevenly. Not saying that is the rule, just what I understand.
Hope this helps