Caliber is the decimal-inch diameter of the gun barrel. For example the land to
land diameter of a 54 caliber rifle is 54/100's of an inch.
The gauge of a gun is the measurement of the bore of the gun in terms of the number
of lead balls of the same diameter that would weigh a pound. For example a 20 gauge
Northwest Trade gun would require balls of a size such that 20 balls would weigh
In the early 1800’s, a man was much more likely to refer to the bore diameter of
his gun in terms of balls per pound than in gauge or caliber. "The rifle I use when
I hunt large game shoots 30 balls per pound."