What was the largest caliber shotgun made?

Answer 1

The largest EVER made was a 2 gauge. It holds a 2 pound metal ball, if I remember correctly.

According the gauge index, a 2 gauge shotgun would hold two half pound balls since the diameter of the shotgun tube determines the gauge, the number of balls to equal a pound going down the barrel in this case would only be two to make a pound. Whereas in a 12 gauge, it takes twelve lead balls of the barrel size to make a pound. A two pound meal ball going down the tube would make for a .5 gauge.