The gauge of a shotgun goes down as the caliber goes up. For instance, the standard 12 gauge is equal to a 0.72-inch caliber, but is a small fry compared to the giant 2-gauge punt guns used in the 19th century. These formidable weapons were used for commercial hunting, bringing down whole flocks of wildfowl with a single blast. They were later taken up by sportsmen.
Too heavy to be lifted, the punt gun was fired from a rest in a one-man boat. The barrel was equivalent to 1.3-inch caliber and could fire a load equal to about 40 standard 12-gauge shells. Punt gunning
proved so effective at killing flocks of birds that many states outlawed it by 1860.