Largest pistol caliber?

I was watching something on History Channel the other day on trick shooters. It was very interesting and had segments on Annie Oakley, John Wesley Hardin and Buffalo Bill and Bill Hickock. They also had some demonstrations by modern sharpshooters and trick shots. They had some guy (I didn't get his name) shooting the most powerful calbre handgun. I thought it was a .50 calibre, but he had one larger! It was HUGE, a cannon!! Does anyone know what calibre is the largest commercially available in the US?

When I watched it I said, "I WANT THAT FOR CHRISTMAS!!!"



MarMac