Well, I've never had this happen, but if it were mine I would hold it firmly by the barrel and forearm and give it two whacks with a rubber hammer, one on the rear and one on the front, both at the heel of the grip. Make sure they are front to back or back to front whacks; sideways can crack the grip where it goes up on the sides of the frame. If that didn't work, I might give it two more whacks, slightly harder. Do this over a carpeted floor, and let us know what happens.
RonF