https://en.wikipedia.org/wiki/Frank_%22Cannonball%22_Richards said:
Richards began by letting people (including heavyweight champion Jack Dempsey) punch him in the gut. Dempsey hit him in the stomach a reported total of seventy-five times.[2] He then progressed to letting people jump on his belly, being struck by a two-by-four, being struck by a sledgehammer, and finally being shot by a 104-lb. (47 kg) cannonball from a spring-loaded 12 ft. (3.6 m) cannon.[3] Richards limited his cannonball act to twice per day, as performing it more often was too painful.