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Meet Frank "Cannonball" Richards, whose stunt involves having a cannonball shot into his big beefy belly!
The Human Marvel has more on "Cannonball" Richards:
‘Cannonball’ Richards steadily increased the level of distress he subjected his belly too. He soon allowed spectators to jump on his stomach. Following that he allowed himself to be struck by a two-by-four and then, later, he was able to endure repeated sledgehammer blows. From all reports and records, there were no gimmicks at work during these performances.
Finally, in a feat that ‘Cannonball’ Richards would forever be remembered for, Richards took to being shot in the belly with a cannonball.
Link - Thanks J. Tithonus Pednaud!